Evolutionary Biology

The Darwinian Revolutions

Part One
Allen D. MacNeill
Cornell University

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 Evolutionary Biology
The Darwinian Revolutions
Part One
Allen D. MacNeill

Executive Editor
Donna F. Carnahan

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COURSE GUIDE
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 Course Syllabus

Evolutionary Biology
The Darwinian Revolutions
Part One

About Your Lecturer ................................................................................................4

Introduction ............................................................................................................5

Lecture 1 Darwin’s Revolutionary Idea ...........................................................6

Lecture 2 Consensus and Controversy............................................................9

Lecture 3 Doing Science ..............................................................................17

Lecture 4 Chance and Necessity...................................................................25

Lecture 5 The Origin of the Origin ..............................................................31

Lecture 6 The Darwinian Manifesto: Natural Selection .................................38

Lecture 7 The Darwinian Manifesto: Descent with Modification ...................46

Lecture 8 Mendel’s Dangerous Idea..............................................................52

Lecture 9 Equilibrium Violated: The Hardy-Weinberg Law ............................59

Lecture 10 Fisher, Haldane, and Wright..........................................................64

Lecture 11 Natural Selection and Speciation ...................................................69

Lecture 12 Disturbing Implications.................................................................76

Lecture 13 Disastrous Digressions ..................................................................84

Lecture 14 A Temporary Unity .......................................................................94

Course Materials .................................................................................................101

Recorded Books ..................................................................................................104

3
Photo courtesy of Allen D. MacNeill

About Your Lecturer

Allen D. MacNeill
Allen MacNeill earned a B.S. in biology in 1974 and an M.A. in science
education from Cornell in 1977. He has taught the support course for intro-
ductory biology at Cornell University since 1976. As a senior lecturer in the
Learning Strategies Center at Cornell, MacNeill works with students taking
both majors and non-majors introductory biology. In addition, he organizes
and carries out in-service training for teaching assistants in biology and
related fields. MacNeill also teaches evolution for the Cornell Summer
Session and has taught the introductory evolution course for non-majors at
Cornell. He has served as a Faculty Fellow at Ecology House and as an hon-
orary member and faculty advisor for the Cornell chapter of the Golden Key
International Honour Society. He has served on numerous advisory commit-
tees and editorial boards at Cornell and in the Ithaca community.
Allen MacNeill’s The Evolution List blog (http://evolutionlist.blogspot.com)
is a forum for commentary, discussion, essays, news, and reviews that illu-
minate the theory of evolution and its implications.
A useful resource for MacNeill’s first two
Modern Scholar courses, Evolutionary Psychology
I (2010) and Evolutionary Psychology II (2011), is
his companion blog Evolutionary Psychology
(http://evolpsychology.blogspot.com).
Along with his many teaching assignments,
C
Books, LL

MacNeill has appeared in a number of Off-

Broadway plays and in other acting venues.
d
© Recorde
C
Books, LL
d
© Recorde

4
 Introduction
The theory of evolution is one of the most profound ideas ever entertained
by the human mind. It fundamentally alters our perception of reality. In
profound and unsettling ways, the theory of evolution changes our under-
standing of who we are, where we come from, why we do the things we
do, and where we might be going. It does this by making us look carefully
and dispassionately at the world around us, asking questions and seeking
answers in the things we can see and hear and smell and taste and touch.
It forces us to look beyond ourselves and our immediate surroundings, and
to make educated guesses about things that have happened that we cannot
directly observe. And it requires us to think long and hard about what is
real and what isn’t.
Ideas, like species, have origins. Like most profound ideas, the idea that
the world has changed, is changing, and will change has very deep roots.
In this lecture series we will trace the beginnings of the idea of evolution,
from its origins in the thoughts and writings of the philosophers of ancient
Greece, through the careful and detailed observations of the great natural-
ists of the nineteenth century, through the revolutionary theoretical work of
the founders of the “modern evolutionary synthesis,” to the fascinating dis-
coveries being made every day by experimental scientists and field biolo-
gists. As we do so, our emphasis will always be on understanding where
the ideas come from and what they imply about our understanding of the
natural world—about reality itself.
Daniel Dennett, a historian and philosopher of evolutionary biology, has
likened the theory of evolution to a “universal acid” that can dissolve all of
the beliefs we hold most dear. In his most famous book, Darwin’s Dangerous
Idea, Dennett argues that the philosophical and religious implications of evo-
lutionary biology fundamentally undermine many of the central principles
upon which Western civilization is based. And indeed, evolutionary theory
and the philosophical assumptions upon which it is based are largely incom-
patible with such traditional ideas as universal purpose, benign (or malig-
nant) nature, gods or other supernatural entities that can intervene in
human affairs, and human free will.
However, evolutionary theory can also be thought of as a tool, one of the
sharpest and most useful tools humans have ever devised. Like any very
sharp tool, evolutionary theory is dangerous, and should not be bandied
about without training in its use and an appreciation for its uses and
abuses. That is what we will cultivate throughout this lecture series: an
understanding and appreciation of the power and potential—and beauty—
of evolutionary theory.

5
Lecture 1
Darwin’s Revolutionary Idea
The Suggested Reading for this lecture is Ernst Mayr’s What Evolution Is.

Evolution is change. Since the publication of Charles Darwin’s Origin of

Species, the term “evolution” has had a more specific meaning, especially
among naturalists and scientists. To a scientist, evolution means the process
by which biological organisms and their characteristics have changed over
time. For this reason, scientists often refer to the evolution of life and living
things as biological evolution, and the scientific study of biological evolu-
tion is usually referred to as evolutionary biology.
Evolution is a process. The theory of evolution describes the processes
whereby organisms (and their various parts) change over time. This process
depends on four characteristics of living organisms.
1. Variety: structural and functional differences between individuals
in populations.
2. Heredity: the inheritance of structures and functions from parents
to offspring.
3. Fecundity: the ability to reproduce, especially at a rate that
exceeds replacement.
4. Demography: the idea that some individuals survive and reproduce
more often than others.
As a result of these four preconditions, the heritable characteristics of
some individuals become more common in populations over time. The pat-
tern of changes that occur in the heritable characteristics present among
the surviving members of populations is what we call biological evolution.
Evolution is a theory. The theory of evolution is a scientific explanation for
how living organisms interact with their environment, producing the
changes we observe in the characteristics of living organisms in popula-
tions, in their genes, and in the fossils of organisms that have died and
were preserved. A scientific theory is a provisional explanation for a natural
phenomenon that is accepted by most scientists as the best explanation for
that phenomenon, given the observable evidence available at the time. The
theory of evolution has two related parts:
1. An explanation for the mechanisms by which evolutionary change
has occurred.
2. An explanation for the patterns of change that we infer from com-
parative anatomy, comparative genetics, and the fossil record.

6
 Evolution is a worldview. The theory of evolution has been formulated,
tested, and expanded according to a particular view of reality—a world-
view—shared by virtually all scientists. There are many distinct and some-
times contradictory worldviews held by people from different backgrounds
and traditions. Each of us holds a personal worldview, and groups of people
share public worldviews. The public worldview shared by virtually all scien-
tists is called naturalism.
The theory of evolution is an idea. As we observe and interact with the
world around us, we formulate explanations about what things are, about
how things happen, and why they happen. These explanations are not the
objects and events themselves. Rather, they are ideas about those objects
and events. The idea that things have changed, are changing, and will con-
tinue to change—the idea of change—seems simple. Yet, the idea that evo-
lution has occurred, is occurring, and will continue to occur is difficult for
many people to even accept, much less understand.
Ideas have origins. In this lecture series we will trace the beginnings of
the idea of evolution, from its origins in the thoughts and writings of the
philosophers of ancient Greece and Rome, through the careful and detailed
observations of the great naturalists of the eighteenth and nineteenth cen-
turies, through the revolutionary theoretical work of the founders of the
“modern evolutionary synthesis,” to the experimental scientists and field
biologists of today.
Ideas have contexts. Ideas generally don’t come out of nowhere. They have
a context and arise out of other ideas at particular times and in particular
places. Ideas make more sense when we understand where they come
from, what other ideas led to them, and the historical and sociological con-
text within which they arose.
Scientific ideas require evidence. Ideas are generally about something
(even when they are about nothing). That is, we formulate and adopt ideas
on the basis of what we know and understand about reality. The theory of
evolution is part of the natural sciences. As such, the idea of evolution is
ultimately based on observation of nature and natural processes, and it
requires evidence.
Ideas have consequences. Ideas are born, live, reproduce, and die in our
minds, and they can be transmitted to other minds. As they do so, they
influence other ideas and thereby shape our understanding of reality. This
means that they also change the way we behave. Ideas are encoded in pat-
terns of chemical and electrical activity in our sensory, nervous, and motor
systems, and therefore they are causally linked to the things we do, not just
to the things we think. Our ability to conform our behavior to our ideas is
clearly imperfect, but it exists nonetheless. Therefore, to succeed in con-
forming our behavior to our ideas, we should make certain that our ideas
conform to reality.

7
 FOR GREATER UNDERSTANDING

Questions
1. What are the prerequisites for biological evolution and what is the out-
come, given those prerequisites?
2. What is the worldview of most scientists and how does it differ from that
of most of the general public?
3. What two main ideas did Darwin present in the Origin of Species and
how are they related to each other?

Suggested Reading
Mayr, Ernst. What Evolution Is. New York: Basic Books, 2002.

Other Books of Interest

Dennett, Daniel C. Darwin’s Dangerous Idea: Evolution and the Meanings
of Life. New York: Simon & Schuster, 1996.
Larson, Edward J. Evolution: The Remarkable History of a Scientific Theory.
New York: Modern Library, 2006.

Websites of Interest
1. The Cornell University Cyber Tower website features a video study room
entitled “Darwinian Revolutions,” which is a six-part series hosted by
Allen MacNeill at the Museum of the Earth at the Paleontological
Research Institution in Ithaca, New York. —
http://cybertower.cornell.edu/lodetails.cfm?id=421
2. The Understanding Evolution website at the University of California
Museum of Paleontology (Berkeley, CA) provides fundamental informa-
tion on evolution, teaching materials, and resources on the topic. —
http://evolution.berkeley.edu
3. The PBS Nova Evolution website features resources for teachers, stu-
dents, and the general public from the television series and ongoing
research on evolution. — http://www.pbs.org/wgbh/evolution

8
Lecture 2
Consensus and Controversy
The Suggested Reading for this lecture is Eugenie C. Scott’s Evolution vs.
Creationism: An Introduction.

You’re heading down the street, when suddenly you come upon a smoking
pile of wreckage—what looks like it was once a house. From the evidence
you can see (and hear and smell), there are at least three possibilities:
1. There has been a house fire, which started accidentally.
2. There has been a house fire, which was set on purpose.
3. Someone has staged what looks like the aftermath of a house fire.
How can you tell the difference? Consider the following:
• You did not witness a house fire, only what looks like its aftermath.
• All you have available to you to answer this question is what you
can see, smell, hear, touch, and so forth.
Now consider your three alternative explanations:
1. Can you be absolutely certain that the house fire (if there was one)
happened by accident?
2. Can you be absolutely certain that it didn’t happen on purpose?
3. Can you be absolutely certain that it hasn’t been staged?
If you answer these questions from the viewpoint of a scientist, your
answer to all three must be no. All you have to go on is what you can
observe now, and what you observe now is not a house fire, but evidence
that one might have happened. So how do you decide which explanation is
most likely?
The answer, if you are a scientist, is that you provisionally accept the
explanation that best fits what you have observed, along with your knowl-
edge of similar events you have observed in the past.
What you are doing when you make a guess like this is inferring that an
event that you have not witnessed has, indeed, taken place. This is precise-
ly what evolutionary biologists do when they study evidence that indicates
that evolution has occurred in the past. Inference is the basis for almost all
reasoning, including scientific reasoning.
Now consider the following:
In crossing a heath, suppose I pitched my foot against a stone, and
were asked how the stone came to be there; I might possibly
answer, that, for any thing I knew to the contrary, it had lain there
forever: nor would it perhaps be very easy to show the absurdity of
this answer.
9
 But suppose I had found a watch upon the ground, and it should be
inquired how the watch happened to be in that place; I should hardly
think of the answer which I had before given, that, for any thing I
knew, the watch might have always been there. Yet why should not
this answer serve for the watch as well as for the stone? Why is it not
as admissible in the second case, as in the first? For this reason, and
for no other, . . . that, when we come to inspect the watch, we per-
ceive (what we could not discover in the stone) that its several parts
are framed and put together for a purpose . . . it must have had, for
the cause and author of that construction, an artificer, who understood
its mechanism, and designed its use. This conclusion is invincible.
This passage is from Natural Theology, or Evidences of the Existence and
Attributes of the Deity, by William Paley, an Anglican minister and tutor at
Christ’s College, Cambridge.
As the quotation from Paley’s Natural Theology indicates, most people
have a “feeling” that nature is designed in some deep way. Most religions
agree: The concept of God goes hand-in-hand with the concept of design in
nature. This is even true for most religions that lack a deity.
In addition to an explanation for the “feeling of design” in nature, religions
generally provide their believers with a “feeling of hope.” Houston Smith, a
historian of religion, has said that hope is “our prime resource.” He believes
that hope is essential to psychological and physiological health. Furthermore,
Smith believes that Darwinian evolutionary theory “dashes all such hopes”
and that Darwinian evolution is the antithesis of the best that religions have
to offer. This viewpoint is echoed by many creationists, who assert that the
theory of evolution and the social policies that they believe are derived from
it are responsible for most, if not all, of the ills of modern society.
If this were indeed the case, then there should be a correlation between the
degree of religious belief in a society and its level of moral behavior, or
between the degree of atheism in a society and its degree of moral degradation.
Two international surveys were conducted during 1991 and 1993 by the
International Social Survey Program. This is currently located at the
National Opinion Research Center at the University of Chicago. Seven
“yes” or “no” questions were asked in the survey in 1991:1
God: “I know God exists and I have no doubts about it.”
Afterlife: “I definitely believe in ‘life after death.’”
Bible: “The Bible is the actual word of God and it is to be taken lit-
erally, word for word.”
Devil: “I definitely believe in ‘the Devil.’”
Hell: “I definitely believe in ‘Hell.’”

1. See Table 2.1 on page 14 for survey results.

10
 Heaven: “I definitely believe in ‘Heaven.’”
Miracles: “I definitely believe in ‘religious miracles.’”
In the United States, almost 63 percent of respondents indicated that they
agree that they “know God exists and . . . have no doubts about it.” Only
the Philippines and Poland—both predominantly Catholic countries—
ranked higher than the United States.
The results of another survey2 showed the percentage of persons who said
“yes” to the following question: “In your opinion, is this statement true:
‘Human beings developed from earlier species of animals’?” The results of
this survey are a measure of belief in human evolution and, by implication,
disbelief in creation science.
In stark contrast to the first survey, the United States ranked dead last in
this listing, with less than 35 percent of respondents indicating that they
agree with the statement “Human beings developed from earlier species of
animals.” Also, unlike most of the other questions in the first survey,
which showed a strong positive correlation between the general belief in
God and specific beliefs in such things as the Devil, an afterlife, Heaven,
Hell, and miracles, there is no strong correlation between religious belief
and disbelief in the theory of evolution. For example, only 9 percent of
East Germans had a belief in God, but 82 percent accepted evolution, but
61 percent of Filipinos, 86 percent of whom believed in God, also accept-
ed the theory of evolution.
The United States is often held up as the world leader in science and tech-
nology. However, polling data collected by the Gallup organization indicates
that Americans do not support science and scientific ideas when they have
to do with evolution. Beginning in 1982, the Gallup organization has polled
Americans on the subject of evolution versus creationism. At Cornell
University, we have conducted similar polls in our biology and evolution
courses over the same period of time. In both sets of polls, respondents
were asked with which of three statements they agreed:3
1. God created man pretty much in his present form at one time within the
last 10,000 years. This is the position of most “young-Earth creationists.”
2. Man developed over millions of years from less advanced forms of life,
but God guided this process, including mankind’s creation. This is the
position of most supporters of “intelligent design.”
3. Man developed over millions of years from less developed forms of life.
God had no part in this process. This is the position of almost all evolu-
tionary biologists.

2. See Table 2.2 on page 14 for survey results.

3. See Table 2.3 on page 15 for survey results.

11
 The differences could hardly be more stark: 90 percent of Americans
believe that God has guided human evolution, with almost half of them
agreeing that humans have not evolved at all. By contrast, 95 percent of
American scientists believe that humans have evolved over millions of years
by a process in which God played no part (the same percentages hold for
students at Cornell). This leads many people to ask the question: Do
American scientists believe in God?
James H. Leuba conducted a poll of American scientists in 1914, asking
whether they believed, disbelieved, or were agnostics about this statement:
I believe in a God in intellectual and affective communication with
mankind, i.e., a God to whom one may pray in expectation of receiving
an answer. By “answer” I do not mean the subjective, psychological
effect of prayer.
The results of Leuba’s poll indicated that in 1914, the percentage of
American scientists who believed in God was 42 percent, while the per-
centage of American scientists who disbelieved in God was 41 percent,
with 17 percent agnostics on the question.
Leuba repeated his poll of American scientists in 1933 and found that the
percentage of American scientists who believed in God was 15 percent,
while the percentage of American scientists who disbelieved in God was 68
percent, with 17 percent remaining agnostics on the question.
This was a dramatic change. What happened to cause such a change?
One significant event that almost certainly influenced the beliefs of some
American scientists was the famous “Scopes monkey trial,” which took
place in the summer of 1925 in Dayton, Tennessee. John T. Scopes was a
high school biology teacher who was arrested and charged with violating
Tennessee’s Butler Act.
Scopes was defended by renowned trial lawyer and atheist Clarence
Darrow, while the prosecution was assisted by populist and former presi-
dential candidate William Jennings Bryan. While Scopes was found guilty of
violating the law, the trial created a sensation in the press, with H.L.
Menken portraying the people of Tennessee and the supporters of the
Butler Act as uneducated, illiterate, anti-science rubes. Scientists, and espe-
cially evolutionary biologists, followed the trial and its outcome closely and
could not help but notice that their own discipline was under attack. By
1933, the average American scientist had become an atheist.
What about today? In 1998, Edward J. Larson and Larry Witham conducted
a poll similar to the one conducted by the Gallup organization, this time
focusing on members of the National Academy of Sciences. They found that
the percentage of members of the National Academy of Sciences who
believed in God was 7 percent, while the percentage of members of the
National Academy of Sciences who disbelieved in God was 73 percent,
with 20 percent remaining agnostics on the question.

12
 In 2004, Gregory Graffin, a PhD graduate student in evolutionary biology
at Cornell University under Professor William Provine, conducted a similar
study, this time polling evolutionary biologists who were members of the
national academies of sciences in countries throughout the world.
The percentage of members of the national academies of sciences of twen-
ty-three major countries who believed in God was 5 percent, while the per-
centage of members of the national academies of sciences who disbelieved
in God was 87 percent, with 8 percent agnostics.
The overwhelming majority of scientists, then, and especially evolutionary
biologists, do not believe in God, especially a God who is in personal con-
tact with us and who has created humans or guided our evolution.
What is the connection between the concept of design in nature and the
theory of evolution by natural selection?
While there may have been a place for a supernatural deity at the begin-
ning of time, to establish the laws of nature and set them in motion, that
would be the first and last time that such an entity intervened in natural
processes. If those laws were sufficiently comprehensive, then further inter-
vention in nature by its creator would be unnecessary. As many theolo-
gians, along with Cornell evolutionary biologist and historian of science
William Provine, have pointed out, such a deity would not in any way be
contradicted by the theory of evolution.
This has led to a perennial controversy in American public policy, in which
creationists demand that laws be passed to either prohibit the teaching of
evolutionary theory in the public schools or, if it is allowed, to require that
the religious creation story from the Bible be taught along with it. However,
the United States Constitution has been interpreted in multiple civil court
decisions, including a series of Supreme Court decisions, to prohibit the
teaching of creationism or “intelligent design” in American public schools
(as constituting an “establishment of religion”) and to allow the teaching of
the theory of evolution as accepted by scientists.
This situation is almost unique to the theory of evolution by natural selec-
tion. No other scientific theory, with the possible exception of Einstein’s
theory of relativity, has met with such intense and sustained opposition.
And, as the survey results outlined earlier indicate, there is a greater dis-
connect between the public perception and acceptance of a scientific theory
and its acceptance by the scientific community. Clearly, something about
the theory of evolution by natural selection repels nonscientists as much as
it appeals to scientists.

13
 Table 2.1
Descending Order by Percent of Belief In
Country God Afterlife Bible Devil Hell Heaven Miracles Evolution
Philippines 86.2 35.2 53.7 28.3 29.6 41.9 27.7 60.9
Poland 66.3 37.8 37.4 15.4 21.4 38.6 22.7 35.4
United States 62.8 55.0 33.5 45.4 49.6 63.1 45.6 <35.4
N. Ireland 61.4 53.5 32.7 43.1 47.9 63.7 44.2 51.5
Ireland 58.7 45.9 24.9 24.8 25.9 51.8 36.9 60.1
Italy 51.4 34.8 27.0 20.4 21.7 27.9 32.9 65.2
Israel 43.0 21.9 26.7 12.6 22.5 24.0 26.4 56.9
Hungary 30.1 10.6 19.2 4.2 5.8 9.4 8.2 62.8
New Zealand 29.3 35.5 9.4 21.4 18.7 32.2 23.1 66.3
W. Germany 27.3 24.4 12.5 9.5 9.3 18.2 22.7 72.7
Netherlands 24.7 26.7 8.4 13.3 11.1 21.1 10.2 58.6
Great Britain 23.8 26.5 7.0 12.7 12.8 24.6 15.3 76.7
Slovenia 21.9 11.6 22.3 6.9 8.3 9.5 13.4 60.7
Norway 20.1 31.6 11.2 13.1 11.4 23.0 17.8 65.0
Russia 12.4 16.8 9.9 12.5 13.0 14.7 18.7 41.4
E. Germany 9.2 6.1 7.5 3.6 2.6 10.2 11.8 81.6

Table 2.2
Descending Order by Percent of Belief In
Country God Afterlife Bible Devil Hell Heaven Miracles Evolution
E. Germany 9.2 6.1 7.5 3.6 2.6 10.2 11.8 81.6
Great Britain 23.8 26.5 7.0 12.7 12.8 24.6 15.3 76.7
W. Germany 27.3 24.4 12.5 9.5 9.3 18.2 22.7 72.7
New Zealand 29.3 35.5 9.4 21.4 18.7 32.2 23.1 66.3
Italy 51.4 34.8 27.0 20.4 21.7 27.9 32.9 65.2
Norway 20.1 31.6 11.2 13.1 11.4 23.0 17.8 65.0
Hungary 30.1 10.6 19.2 4.2 5.8 9.4 8.2 62.8
Philippines 86.2 35.2 53.7 28.3 29.6 41.9 27.7 60.9
Slovenia 21.9 11.6 22.3 6.9 8.3 9.5 13.4 60.7
Ireland 58.7 45.9 24.9 24.8 25.9 51.8 36.9 60.1
Netherlands 24.7 26.7 8.4 13.3 11.1 21.1 10.2 58.6
Israel 43.0 21.9 26.7 12.6 22.5 24.0 26.4 56.9
N. Ireland 61.4 53.5 32.7 43.1 47.9 63.7 44.2 51.5
Russia 12.4 16.8 9.9 12.5 13.0 14.7 18.7 41.4
Poland 66.3 37.8 37.4 15.4 21.4 38.6 22.7 35.4
United States 62.8 55.0 33.5 45.4 49.6 63.1 45.6 <35.4

14
 Table 2.3
Evolution Poll Results
(expressed as percents)

Gallup Poll Cornell

Evolution
General College American Course
Public Graduates Scientists 2001–2009
Young Earth Creationist 44 24 5 5
God-Guided Evolution 46 59 40 41
Unguided Evolution 10 17 55 54

15
 FOR GREATER UNDERSTANDING

Questions
1. Why are design and purpose excluded from scientific explanations,
especially the theory of evolution?
2. Some supporters of “intelligent design” assert that it is not an inherently
religious concept and therefore can be legally taught in the public schools.
Is this assertion valid and, if so, on what grounds? If not, why not?
3. Does the training that accompanies becoming an evolutionary biologist
cause one to become an atheist or agnostic, or are atheists and agnostics
predisposed toward pursuing a career in the science of evolutionary biol-
ogy, or both?

Suggested Reading
Scott, Eugenie C. Evolution vs. Creationism: An Introduction. 2nd ed.
Berkeley: University of California Press, 2009.

Other Books of Interest

Larson, Edward J. The Creation-Evolution Debate: Historical Perspectives.
Athens, GA: University of Georgia Press, 2007.
National Academy of Sciences. Teaching about Evolution and the Nature of
Science. Washington, DC: National Academies Press, 1998.

Websites of Interest
1. The National Academy of Sciences website provides its publication
Science and Creationism, 2nd ed. (1999). —
http://www.nap.edu/openbook.php?record_id=6024
2. The National Center for Science Education website provides an article
by Peter M. J. Hess, Director, Religious Community Outreach (2009),
entitled “Science and Religion.” — http://ncse.com/religion
3. The TalkOrigins Archive website is devoted to the discussion and debate
of biological and physical origins. —
http://www.talkorigins.org/origins/faqs.html
4. The Complete Work of Charles Darwin Online website features William
Paley’s Natural Theology, or Evidences of the Existence and Attributes of
the Deity, Collected from the Appearances of Nature (1802). —
http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=
A142&pageseq=1

16
Lecture 3
Doing Science
The Suggested Reading for this lecture is Karl R. Popper’s The Logic of
Scientific Discovery.

Imagine that you are an alien explorer from a planet that does not have
fruit trees. As you leave your spacecraft, you walk through an apple orchard
and a green apple falls from a tree and bounces off your head.
You could ask, “What is this object that just bounced off my head? “What”
questions ask for a description. Scientists often ask “what” questions about
things in the world around us. The answers to such questions collectively
constitute what could be called descriptive science. Until the twentieth
century, much of biology was primarily descriptive.
Another question you could ask about the apple is, “How did this object
fall from the tree and hit my head? “How” questions ask for an analysis.
Scientific analysis often involves “taking apart” something to better under-
stand the interactions and relationships between its constituent parts. This
process is often called scientific reductionism, which means that the phe-
nomenon is analyzed by “reducing” it to some simpler or more basic parts
or principles.
Scientific analyses often focus on causes. In our apple example, you could
say that the force of gravity caused the green apple to fall to the ground.
Implicit in this analysis is the flow of time. When something causes some-
thing else, an event has occurred in time, with the cause preceding the
effect that it brings about. One of the most basic principles of natural sci-
ence is that effects cannot precede causes.
There are at least four major causes of evolutionary change:
1. mutation
2. genetic drift
3. natural selection
4. sexual selection
All four of these processes cause observable changes in the structural,
functional, and genetic characteristics of populations of living organisms.
Two of these processes—mutation and genetic drift—are random as far as
we can tell, while two of them—natural selection and sexual selection—are
not. All of these changes happen over time (often very long periods of
time). As in all natural processes, the causes of evolutionary change precede
their effects.
Scientists often ask “how” questions about events in the world around
us. The answers to such questions constitute what could be called

17
analytical science. Biology didn’t become a fully analytical science until
the twentieth century.
“Why” questions ask for an explanation. Traditionally, “why” questions
focus on the “reasons” for events, that is, the details and dimensions of the
“plans” for the events that resulted in their occurrence.
Asking for an explanation (as opposed to an analysis) is appropriate when
you are interested in the reason why a person does something. A simple
answer to the question “Why are you listening to this lecture?” might be
“In order to learn more about evolution.” Humans can “reason” about
things: we can think about reality, make plans for the future, and conform
our behavior to those plans (more or less).
Notice the phrase “in order to.” Why do we say that we are doing some-
thing “in order to” accomplish some end? Because time order is central to
such explanations: you are listening to this lecture in order to learn more
about evolution. That is, we perform some action first “in order to” bring
about some result afterward.
This is essentially the same time order as causes and effects; causes pre-
cede their effects in the same way that means precede ends. However,
there is a crucial difference: causes and effects do not require intentions or
plans, but means and ends do.
Intentional processes, in other words, seem to involve an inversion of the
relationship between causes and effects as observed in nature. We know
this because if we are prevented from accomplishing our goal—learning
about evolution—we can still accomplish it by coming back to this lecture
or by listening to another lecture or reading a book on the subject. Goal-ori-
ented behavior involves compensation for deflection from the goal in such a
way that if one is deflected from one’s goal, it is still possible to accomplish
it by shifting to alternative means.
This does not happen in purely natural, nonintentional processes. If an
apple falls from a tree and a table intervenes, the apple does not dodge the
table “in order to” reach the ground. The natural sciences are founded on
this principle: natural causes do not include intentions, purposes, or plans.
In the natural sciences, “how” questions and “why” questions have the
same answer. To a scientist, the analysis of a natural event and its explana-
tion are exactly the same. That this is the case is virtually universally
accepted by all natural scientists. It is, however, the source of much misun-
derstanding about science and scientific reasoning, and a source of much of
the uneasiness people feel when they are first exposed to the theory of evo-
lution by natural selection.
Science
The word science by itself simply means “knowledge,” which can come in
an almost infinite variety of forms, only some of which are what we would

18
commonly recognize as “science.” Furthermore, there is more than one
kind of knowledge that can be called “science.” To simplify somewhat,
there are at least two kinds of “science”: empirical and nonempirical.
Empirical sciences are ultimately based on the observation of nature and
natural processes. Most people use the term science to refer to the various
empirical sciences, such as astronomy, biology, chemistry, geology, physics,
and so forth. In all of these empirical sciences, the various scientific princi-
ples, laws, and theories are ultimately based on observation of nature and
natural processes. For this reason, the empirical sciences are often called
the natural sciences.
Scientists working in the natural sciences assume that only those objects
and processes that can be either directly or indirectly observed should be
used to formulate scientific descriptions, analyses, and explanations: Only
nature matters when doing science.
To a scientist, all natural objects and processes can, and therefore should,
be completely understood and explained simply by referring to other natur-
al objects and processes, without reference to supernatural entities or
forces. This assumption, which is shared by virtually all scientists, is often
referred to as naturalism. Because empirical scientists study nature, the
common assumption that determines the methods they use to study nature
is called methodological naturalism. Virtually all natural scientists who have
thought about these issues agree that methodological naturalism is the
absolute foundation of all of the natural sciences.
Like all natural sciences, the theory of evolution has been formulated
based on methodological naturalism. Evolutionary biologists, like all empiri-
cal scientists, assume that the only valid scientific principles are those that
have been formulated on the basis of empirical observation of nature and
natural processes.
Scientific explanation involves several types of logical reasoning. Let’s
assume that you’ve never tasted a green apple before. It’s sour and you
might be tempted to conclude that “green apples are sour.” However,
you’ve only tasted one green apple. Therefore, the only thing that you can
legitimately conclude is that this particular green apple is sour.
Having tasted one green apple, you sample another. The first thing you
need to verify is that you are sampling the same thing—that the second
object you sampled is the same as the first. To do this, you use what is per-
haps the most widely used (but least widely recognized) form of logical rea-
soning: reasoning by analogy.
An analogy is a perceived similarity between two or more objects or
processes. When you sample your second green apple, you logically
assume that it has properties that are similar enough to those of the first
that you can come to valid conclusions about green apples as a class of
similar objects.
19
 The kind of logic you use to make statements about classes of similar
objects or processes is sometimes called transductive reasoning, which is the
simplest form of logical reasoning. It is also absolutely necessary for all other
forms of logical reasoning. Without the ability to recognize similarities
between distinct objects and processes, it would be impossible to say any-
thing about collective classes or groups of objects, and therefore to formulate
generalizations (and to use generalizations to formulate specific examples).
However, transductive reasoning by itself is the weakest form of logical
argument. Analogies, by definition, are not “true” statements. An analo-
gy is not a statement of an observable fact; it is simply a statement of
logical relationship.
You’ve now tasted two green apples. You can therefore conclude that the
second green apple is similar enough to the first to come to a conclusion
about the two apples as an identifiable class of similar objects. And then
you sample another green apple, and another, and yet another. Eventually
you sample enough that turn out to be sour that you can formulate a gen-
eral statement (a “generalization”) about green apples as a collective group
or class: you conclude, on the basis of repeated observations, that green
apples are sour.
How confident can you be that your generalization is valid? If you think
back on the series of observations you made, you should realize that your
generalization is only as good as the number and consistency of the obser-
vations you made. The more observations you make, the more confident
you can be that any conclusions are valid. Logical reasoning that conforms
to this pattern of repeated observation, followed by an inferred generaliza-
tion, is called inductive reasoning (also called induction).
First, inductive reasoning can never prove any generalization with absolute
certainty. No matter how many similar observations one has made, this
does not absolutely guarantee that every possible observation about every
single member of a logical class will turn out the same.
Second, all conclusions based on inductive reasoning are provisional. They
are only valid up to the moment of the most recent observation. As implied
in the first statement, it may turn out that the next observation will contra-
dict any prior generalization.
Finally, all scientific reasoning begins with, and is ultimately based on,
inductive reasoning. Therefore, all scientific descriptions, principles, theo-
ries, and laws have the characteristics listed above.
In many cases, scientists are unwilling to base their conclusions on a rela-
tively small number of simple observations. Instead, most scientists attempt
to further validate their conclusions by making one or more predictions
based on their original generalizations, and then testing those predictions
using further observations. This process—arguing from a generalization to
specific cases—is known as deductive reasoning (also called deduction).
20
 A classical example of deductive reasoning is called a syllogism. Here’s
an example:
• Scientists wear white lab coats.
• Jane is a scientist.
• Therefore, Jane wears a white lab coat.
Is this true? No; Jane Goodall is a famous scientist, but, as far as I am
aware, she has never worn a white lab coat.
What this example demonstrates is that the “truth” of any syllogism
absolutely depends on the validity of its beginning generalization.
Therefore, although the conclusion in the syllogism listed above—that Jane
wears a white lab coat—follows logically from the starting generalization
(and is therefore deductively valid), since the starting generalization is
clearly not valid, the syllogism as a whole is also invalid as an accurate
depiction of reality.
The scientific method usually involves induction, followed by deduc-
tion, followed by empirical testing, followed by statistical verification,
repeated indefinitely.
When a scientist has either formulated a generalization or cited a general-
ization that already exists, that generalization is usually called a hypothesis:
A hypothesis is a generalization about some observable pattern in
objects or events.
A hypothesis can be used to make a prediction that can be used to further
test the validity of that hypothesis. A hypothesis can be tested in one of two
ways: by further simple observation or by experiment. An experiment usual-
ly involves performing and comparing the results of two sets of observations:
an experimental test in which you manipulate the variable that you are test-
ing and a control test in which you do not manipulate the same variable. In
many tests of biological hypotheses, control tests are used to determine if
the variable being manipulated actually affects the outcome. This kind of
investigation is sometimes called experimental science.
In biology in general, and especially in evolutionary biology, many investiga-
tions are essentially discovery science, rather than experimental science. As
we will see, conducting simple observations, without deliberately manipulat-
ing some variable, is still a very powerful method for studying evolution.
Regardless of whether you have tested your hypothesis by simple observa-
tion or by experiment, you aren’t really finished. The next step is to com-
pare your test results with the prediction that you made using your hypoth-
esis. If the results are close to the ones predicted, then you have confirmed
(or “validated”) your hypothesis. However, if the results are significantly
different from the ones you predicted, you take the next (and in many ways
the most important) step: you modify (or completely reformulate) your
hypothesis and repeat all of the steps described above.

21
 In science, a hypothesis that has been repeatedly tested and has not yet
been contradicted by the available evidence is referred to as a theory. A
hypothesis is a tentative guess about the way the world works. When a
scientist uses the word theory, he or she is generally referring to what a
nonscientist would call a scientific law, and the forces and relationships
causing the phenomena described by scientific laws are sometimes
referred to as laws of nature. Notice that although there is no real differ-
ence between a scientific theory and a scientific law, there is a fundamen-
tal difference between a scientific law and the law of nature it describes.
The law of nature is the actual process in physical reality that causes the
regularities in the phenomena under investigation.
A scientific theory is only as reliable as the observations and experiments
that have been done so far to formulate and test it. This means that what
scientists refer to as “theories” generally have a great deal of evidence back-
ing them up, more than alternative explanations.
Nothing is really “true” in science, using the commonly accepted defini-
tion of “truth”—always and absolutely “true.” All scientific theories are
open to revision, and even a cursory look at the history of science indicates
that theories that were once considered “true” are now either highly modi-
fied or have been thrown out altogether.
Much of evolutionary theory is based on logical inference:
You make your best guess, based on the information available and
what you know from past experience.
A common misunderstanding of science is that it can “prove” things. It
can’t, at least not in the sense of “absolute proof.” However, using the sci-
entific method one can disprove things. If you have formulated a hypothe-
sis, made a prediction based on it, tested that prediction, and found it to
not hold for a significant number of samples, then your hypothesis must
either be significantly altered or thrown out entirely.
Karl Popper, possibly the greatest philosopher of science of the twentieth
century, argued that to be considered scientific, a hypothesis must be falsifi-
able. It must be possible to observe evidence that would contradict, and
therefore falsify, that hypothesis.
Popper’s definition of what is and isn’t scientific makes it seem like doing
science is a smooth progression from initial observations to formulating a
hypothesis to prediction to testing to statistical verification to either confir-
mation of the original hypothesis as a theory or disconfirmation and formula-
tion of new hypotheses. But an examination of the actual history of science
presents a different picture. Instead of smooth and steady “progress,” what
often happens is that theories remain relatively unchanged for a period of
time, and then are relatively suddenly overturned during what historian and
philosopher of science Thomas Kuhn has called a scientific revolution.

22
 According to Kuhn’s model of the evolution of science, theories (or “laws”)
are used by scientists to do what he called normal science. This is the collec-
tion of data and observations that confirm and extend already widely accept-
ed theoretical models of nature and physical reality. However, as scientists
practice normal science, they encounter anomalies: observations that do not
fit the already established model, which Kuhn referred to as a scientific par-
adigm. Eventually, enough anomalous evidence has accumulated that one or
more scientists formulate a revolutionary hypothesis. This sets in motion a
scientific revolution—what Kuhn called a paradigm shift—in which the old
theories or laws are modified or replaced by new theories.
Charles Darwin’s publication of the Origin of Species in 1859 is one of the
clearest examples of such a paradigm shift. Prior to 1859, the predominant
theory for the origin of life and living organisms was that “God did it.” But,
during the nineteenth century, an avalanche of new observations of fossils
and living organisms from around the world provided the anomalies that
Darwin used to formulate his theory of evolution by natural selection. In so
doing, Darwin set in motion what would eventually be called the science of
biology as we know it today.
Another way to lend confidence to a hypothesis is to show that it is part of
a larger theory that already has considerable empirical support. This is a
form of logical reasoning known as abductive reasoning (also called abduc-
tion). As the name implies, a tentative idea can be abducted into a larger set
of ideas that already have stronger support. When this happens, the tenta-
tive idea gains considerably in credibility, even if it has little direct support.
A similar form of validation is called consilience. According to Edward O.
Wilson, consilience happens when multiple, independent sources of valida-
tion all point to the same conclusion. Consilience is similar to abduction, in
that it tends to strengthen hypotheses and theories without requiring as
much testing and verification as new, untested ideas.
Consilience, like abduction, has played an important part in the establish-
ment and expansion of the concept of evolution in science. As we will see
(and as Wilson and others have pointed out), there are many lines of inves-
tigation in what once appeared to be widely separated fields of knowledge,
all of which are now converging on what could be called a “grand unified
theory of evolution” in the natural and social sciences.

23
 FOR GREATER UNDERSTANDING

Questions
1. Since inductive reasoning cannot produce absolute certainty, is there any
such thing as “truth” in science?
2. It is sometimes asserted that the validity of inferential reasoning increas-
es from transduction through induction, deduction, and abduction, with
consilience providing the greatest degree of confidence in the validity of
one’s generalizations. Is this hierarchy of increasing validity itself valid,
and why (or why not)?

Suggested Reading
Popper, Karl R. The Logic of Scientific Discovery. 2nd ed. New York:
Routledge, 2002.

Other Books of Interest

Feyerabend, Paul. Against Method. 4th ed. New York: Verso Books, 2010.
Kuhn, Thomas S. The Structure of Scientific Revolutions. 3rd ed. Chicago:
University of Chicago Press, 1996.
Wilson, Edward O. Consilience: The Unity of Knowledge. New York:
Vintage, 1999.

Websites of Interest
1. Allen MacNeill provides an article entitled “TIDAC: Identity, Analogy,
and Logical Argument in Science” on the Evolutionary List blog. —
http://evolutionlist.blogspot.com/2009/01/tidac-identity-analogy-and-
logical.html
2. An article in PDF format by William F. McComas (University of Southern
California) entitled “The Principal Elements of the Nature of Science:
Dispelling the Myths.” —
http://coehp.uark.edu/pase/TheMythsOfScience.pdf
3. The University of Rochester (New York) features an article entitled
“Introduction to the Scientific Method” by Professor Frank L.H. Wolfs of
the Department of Physics and Astronomy. —
http://teacher.nsrl.rochester.edu/phy_labs/AppendixE/AppendixE.html

24
Lecture 4
Chance and Necessity
The Suggested Reading for this lecture is Edwin Arthur Burtt’s The
Metaphysical Foundations of Modern Physical Science: A Historical
and Critical Essay.

The idea of change in nature is not new or unusual. Evolution is change,

but as anyone can observe, change happens all the time in nature.
Evolutionary change is not cyclic, like the precession of the seasons or the
development of an individual organism. Evolutionary change, like the flow
of time itself, is unidirectional and irreversible. Even so-called evolutionary
reversions are not really cyclic, as the evolving organisms change over time
into something like (but not the same as) they were before.
The idea of fundamental, irreversible change in nature is deeply unsettling
to many people. On a personal level, most of us are frightened of our
inevitable descent into death, and that fear encourages us to believe that
death is not permanent, but only a transition to something else, something
permanent and unchanging, or at least recurring, cycle after cycle. But evolu-
tion, like death, is irreversible and permanent, as far as we can tell. Natural
selection, the process that Darwin proposed as the engine of evolution,
depends on the birth and death of uncountable living organisms.
The idea of evolution is not new, but it has been a minority view in
Western culture. What we now think of as science began in a place called
Ionia: the coastline of what is now western Turkey (also called Anatolia)
and the islands between it and the Greek mainland. The Ionians were origi-
nally from Greece and settled the Anatolian shore around 3,000 years ago.
In the Ionian cities of Abderra, Colophon, Ephesus, and Miletus, a group of
philosophers laid the foundations for the Western intellectual tradition.
Thales of Miletus (ca. 625–546 BCE) formulated a naturalistic explana-
tion for natural phenomena. Thales is generally recognized as the founder
of Western philosophy and science. In his scientific investigations, Thales
was a true naturalist, asserting that natural phenomena could be studied
using observation and explained with reference to natural, not supernat-
ural, causes.
Anaximander of Miletus described the Earth as being suspended in space
and proposed that humans developed from fish. Anaximander was a con-
temporary of Thales, but unlike him, Anaximander traveled widely through-
out the Mediterranean world. Anaximander is credited with writing the
first scientific treatise, usually referred to by the title On Nature. Also like
Thales, Anaximander asserted that it was possible to explain natural phe-
nomena without invoking the gods. He proposed that “all the heavens and

25
the worlds within them” have sprung from “some boundless nature,” an
idea that is surprisingly similar to the modern theory of the origin of the
universe. Anaximander, like Thales, believed that the Earth was a sphere,
and that it was suspended in empty space, again anticipating basic princi-
ples of modern astronomy.
Most remarkable of Anaximander’s ideas was the proposal that humans
had developed (that is, evolved) from a lower form of life—fish, to be spe-
cific. He drew analogies between infant humans and infant sharks, some of
which are born alive (rather than from eggs), and argued that humans must
have developed from something like them.
Heraclitus of Ephesus (ca. 535–475 BCE) is most famous for asserting that
“all things go and nothing stays . . . you cannot step twice into the same
river.” Even more than Anaximander, Heraclitus was a proponent of change
in the universe. His most famous assertion states that everything in nature
changes in law-like ways. The changes Heraclitus described, in other
words, were not random, but rather followed patterns that could be dis-
cerned through observation and logic. He also asserted that the Earth was
not created, but rather has always existed as part of what he called the cos-
mos. Like Thales and Anaximander, Heraclitus believed in natural laws and
creative processes, rather than supernatural intervention into nature.
However, Heraclitus went beyond Thales and Anaximander in proposing a
linkage between natural laws and human ethics, a linkage that several evo-
lutionary biologists have drawn more recently.
Democritus of Abderra (ca. 460–370 BCE) asserted that “nothing exists
except atoms and the void” and that “all things are the fruit of chance
and necessity.”
Democritus is best known as one of the founders of the atomic theory.
Long before the invention of chemistry, Democritus proposed that all mat-
ter in the universe is composed of atoms. He described atoms as tiny, hard,
“uncuttable,” massy objects of different composition and weight, which
combine to form all material objects. Democritus explained that all of the
characteristics of material objects are the result of the combination and
interaction of different atoms.
Even more radical than his idea of atoms was Democritus’s assertion that
between the atoms in matter there is absolutely nothing—the “void.” This
means that all of nature consists solely of atoms, separated by nothingness.
This is precisely the model of reality that is the basis of modern physics.
The idea that “nothing exists except atoms and the void” is radical
because it rules out any interference or intervention into reality by super-
natural entities or forces. From this, Democritus proposed an even more
radical idea: that “all things are the fruit of chance and necessity.” By this
he meant that all events and the objects that participate in them, includ-
ing ourselves, are the result of either chance (that is, random, accidental

26
interactions) or natural (and therefore “necessary” or inescapable) causes.
Taken to its logical conclusion, Democritus’s model of reality rules out the
intervention into nature by God or gods, and any possibility of “free will”
in the universe, including human free will.
Epicurus (ca. 341–270 BCE) expanded Democritus’s atomic theory, using
it to provide a logical basis for naturalism and to deduce a comprehensive
system of aesthetics (why we find things beautiful/pleasing and ugly/dis-
gusting) and ethics (why actions and the thoughts that motivate them are
right or wrong). Absolutely central to Epicurus’s philosophy was the idea
that all knowledge ultimately comes from sensory perception, and there-
fore from experience. According to this outlook, sense data are the basis
for all generalizations about the nature of reality. The concepts we form as
the result of such generalizations we then relate to each other, and ulti-
mately we build a consistent worldview from them. Like Democritus’s
atomic theory, the Epicurian worldview does not require, and therefore
does not include, any reference to supernatural causes for natural process-
es. Indeed, according to Epicurus, the gods are natural phenomena, just
like anything else we observe. The only difference is that we “observe”
the gods as entities in our minds, rather than as entities that live somehow
outside of us and outside of nature.
Epicurus greatly extended Democritus’s atomic theory, showing how atoms
could be combined to form combinations like molecules, with properties
that combined and went beyond the simple properties of their constituent
atoms. He also proposed that atoms could “swerve” in an undetermined
way, and that this “undetermined movement” could explain the existence
of human “free will.”
The Roman poet Lucretius (99–55 BCE) reinforced and extended Epicurus’s
theories about nature in a long poem entitled De Rerum Natura, or “On the
Nature of Things.” De Rerum Natura is a detailed explanation of how the
philosophy of Epicurus (and his predecessor, Democritus of Abderra) can be
applied to an understanding of nature and natural processes.
Like Epicurus, Lucretius asserted that everything we know about the uni-
verse around us we know because of observations of that universe: sense
data is the basis of all knowledge. This idea, now called empiricism, is the
basis for all of the natural sciences. Also like Epicurus and most modern sci-
entists, Lucretius explained that it is possible to use logical inference to
learn about events one has not observed directly or personally.
Furthermore, Lucretius made it very clear throughout his great poem that
the Earth and all of the things on it had come about by chance and necessi-
ty, rather than by design. Lucretius based this assertion on the observation
that many things we observe in the natural world are imperfect and there-
fore clearly not the result of intelligent design.

27
 Lucretius proposed a theory of evolution by natural selection twenty cen-
turies before Darwin. In Book 5 of De Rerum Natura, he proposed that the
Earth (and the moon and stars) were all formed from atoms that had
clumped together as a result of their “natural tendency” to combine. He
then explained how plants and animals had formed from the material of
which the Earth was composed, and that there was a period of time when
this process produced “monsters” composed of mismatched parts. Finally,
he explained why the animals we see around us today still exist: they
essentially evolved by natural selection, with the well-formed animals sur-
viving and the poorly formed ones dying off.
The philosophers of Ionia laid the groundwork for what would eventually
become the modern natural sciences. But something happened between the
fourth century BC and today, something that would in many ways retard
the progress of science and set the stage for the current warfare between
evolutionary theory and religion. That “something” was the development of
Platonic philosophy.
Plato, who lived from about 428 to 347 BCE, believed that ideal forms,
not natural ones, are the ultimate reality. These were essentially ideas or
concepts that were related to actual, natural objects, but they existed in
the mind rather than in nature. Whose mind? To Plato, the ideal forms
ultimately existed in the mind of a supernatural entity or entities, which
he often equated with the Greek gods or with a creator he referred to as
the “demiurge.”
This philosophical worldview has been called essentialism, because it
emphasizes the “essences” of things, rather than their differences.
Central to this worldview is the idea that such “essences,” including the
human soul, are eternal and unchanging. The most “real” things—the
“essences”—cannot be perceived with the senses at all, but only with the
mind, imperfect as it might be in any individual person.
Notice here, too, the emphasis on the unchanging, eternal quality of the
“essences,” as opposed to natural objects and processes. Natural phenome-
na (that is, the nonessential) are always changing, but “real” phenomena
are not. Here we see the root of the opposition between the evolutionary
worldview and the Platonic worldview.
Most of Plato’s followers agreed wholeheartedly with these teachings and
carried his ideas throughout the Mediterranean world. However, this was
not entirely the case with Plato’s most illustrious pupil, Aristotle.
Aristotle (384–322 BCE) taught that all natural phenomena have four caus-
es, of which the most important were intentions or purposes. Aristotle is
often credited with being the first great naturalist, in the sense of being a
person who studies nature directly and for its own sake, rather than study-
ing abstract concepts such as mathematics. Yet, for all of his careful study of
the natural world, Aristotle was not an evolutionist. On the contrary, he for-

28
mulated and taught a set of ideas that fundamentally contradict the basic
principles of evolutionary biology. Because his writings were so influential,
and because so much of medieval Christian theology was based on his
ideas, Aristotle can be both credited for establishing the discipline of natur-
al history and blamed for retarding a naturalistic model of evolutionary biol-
ogy for more than two thousand years.
Central to Aristotle’s worldview was the idea that everything, both objects
and processes, has causes. This is part of the naturalist worldview.
However, to Aristotle, intentions or purposes were always part of every
cause. He argued that all objects and processes have four causes:
1. A material cause, by which Aristotle meant the “stuff” of which an
object is composed.
2. An efficient cause, by which Aristotle meant the immediate pro-
ducer of the object or process.
3. A formal cause, by which Aristotle meant the category in which an
object may be classified.
4. A final cause, by which Aristotle meant the purpose for which the
object or process is intended.
To Aristotle, all things—objects and processes—have all four causes. This
means that everything has a purpose; all things exist for a reason. This is
one of the two fundamental problems with Aristotle’s worldview from the
standpoint of evolutionary biology. To a natural scientist (and indeed, to
almost anyone living in the modern world), there are many natural objects
and processes that we understand to have no purpose or intentions at all.
Rocks, water, air, fire, stars—the list includes most nonliving things—all
have no purposes or intentions in and of themselves. A living organism may
use one of these things and thereby give it a purpose, but otherwise a rock
(falling or sitting still), water (solid, liquid, or gas), air (moving or not), fire
(a rapid chemical reaction between oxygen and some other material), and
so forth have no preexisting purposes that cause them to exist or do what
they do.
Aristotle also believed that the many and varied types of living organisms
that he had described and classified (what would later be called “species”)
were not only well-defined, but were also permanent and unchanging. He
recognized that change occurs, but he believed that all change in nature
was essentially cyclic, and that therefore no real permanent change occurs.
In this view, Aristotle reverted to the idealism of his teacher, Plato, and in
so doing promulgated a doctrine that made the idea of evolution virtually
unthinkable for two millennia.

29
 FOR GREATER UNDERSTANDING

Questions
1. What was so revolutionary about the ancient Ionian “enlightenment”?
2. Aristotle has often been called “the first naturalist.” However, it is clear
from most of his work that he opposed the worldview known as ontolog-
ical naturalism. Why is this, and is this a contradiction in Aristotle’s
thinking or not?
3. Do Plato’s and Aristotle’s philosophical ideas resonate with modern evo-
lutionary biology or with modern creationism, including “intelligent
design,” or both (or neither) and why?

Suggested Reading
Burtt, Edwin Arthur. The Metaphysical Foundations of Modern Physical
Science: A Historical and Critical Essay. Charleston, SC: BiblioBazaar,
2009 (1924).

Other Books of Interest

Pirsig, Robert M. Zen and the Art of Motorcycle Maintenance: An Inquiry
into Values. New York: Harper Perennial, 2008.
Popper, Karl. The Open Society and Its Enemies: Volume One: The Spell of
Plato. 7th ed. New York: Routledge, 2002 (1971).
Schrödinger, Erwin. “The Ionian Enlightenment.” Pp. 53–68. Nature and
the Greeks and Science and Humanism. Cambridge: Cambridge
University Press, 1996.

Websites of Interest
Allen MacNeill provides an article entitled “Incommensurate Worldviews”
on the Evolutionary List blog. —
http://evolutionlist.blogspot.com/2006/02/incommensurate-
worldviews.html

30
Lecture 5
The Origin of the Origin
The Suggested Readings for this lecture are Edward J. Larson’s Evolution:
The Remarkable History of a Scientific Theory, chapter 1: “Bursting the
Limits of Time” and chapter 2: “A Growing Sense of Progress.”

To understand why modern biologists, and especially evolutionary biolo-

gists, assume the revolutionary and controversial idea that purpose plays no
more part in evolution than it does in physics or chemistry, we need to
look at the historical changes in the ideas of the origin of life. In European
culture, the predominant explanation of the origin of life was originally pro-
vided by the Judeo-Christian Bible:
• All life was created by God approximately 6,000 years ago in a sin-
gle act of creation that took place over four days.
• All forms of life were created in essentially their present form out
of nothing.
• Since that first creation, none of these specially created “kinds” of
living things have changed fundamentally from their originally cre-
ated “kinds.”
This creation myth was combined during the Middle Ages with Plato and
Aristotle’s ideas about “ideal forms” and purposeful causation in nature,
producing a system of beliefs in which the direct intervention by God in
natural processes was necessary for anything to happen anywhere.
During the Scientific Revolution, which began in the sixteenth century and
continues to the present, this situation finally began to change:
• In 1632, Galileo Galilei, in his Dialog Concerning the Two World
Systems, undermined the biblical story of creation by showing that
the Sun, not the Earth, is the center of the universe, an idea that
had first been proposed by Copernicus.
• In 1687, Isaac Newton published Philosophiae Naturalis Principia
Mathematica, now usually called simply the Principia). In it, he laid
out a system of physical laws by which motion could be analyzed,
based on the assumption that all physical motion is the result of
purposeless mechanical forces. This idea—that purpose was unnec-
essary for the explanation of physical phenomena—became a uni-
versal standard in all of the physical sciences within the century fol-
lowing the publication of Newton’s Principia.
• In 1789, Antoine Laurent Lavoisier published his Elementary
Treatise on Chemistry. In it, he presented the basic principles of
modern chemistry, including the conservation of mass and an

31
 explanation of how combustion, photosynthesis, and respiration
were related chemical processes, none of which required supernat-
ural explanations. Again, Lavoisier’s explanations for chemical
reactions did not require any assumption of preexisting purpose or
design in nature.
The idea of evolution has existed as a minority view within Western cul-
ture since the dawn of recorded history. However, it was not until the eigh-
teenth century that the groundwork for a fully scientific theory of evolution
was laid. Ironically, the cornerstone of such a theory was based on the idea
that all life and living organisms were created by God relatively recently.
As the title of Darwin’s Origin of Species implies, the concept of species is
central to the concept of evolution. People have recognized the existence of
what could be called “species” since prehistoric times, but it wasn’t until
the eighteenth century that the concept of species was systematically
defined and recognized by naturalists.
The person who deserves much of the credit for this recognition was Carl
Linnaeus. A Swedish naturalist, Linnaeus is best remembered for his intro-
duction of the system of classification known as binomial nomenclature, by
which every living organism can be classified as a member of a particular
genus and species.
Linnaeus proposed a systematic classification system for plants in his
Systema Naturae, first published in 1735 as a pamphlet of eleven pages. In
it, he proposed that every species of plant could be classified using a two-
part name consisting of a genus and species name. Linnaeus followed com-
mon practice at the time by using Latin as the language in which all plants
would be named and classified.
Linnaeus’s classification scheme was immediately popular with other natu-
ralists, for several reasons:
• First, it allowed all plants, including newly discovered ones, to be
classified relatively quickly and easily on the basis of their reproduc-
tive anatomy.
• Second, Linnaeus’s Systema Naturae classified all plants within a
hierarchical scheme, thereby allowing naturalists to relate species
to each other and to their habitats. This dramatically reduced ambi-
guity in identification and classification, and set the stage for
Darwin’s revolutionary classification system based on descent.
• Linnaeus’s classification scheme was also useful because it was writ-
ten in Latin, the universal language of science at the time. As a
“dead” language, its grammar and vocabulary were fixed and
unchanging, thereby allowing all scientists in all countries to use it
without confusion.

32
 At about the same time that Linnaeus was developing his classification sys-
tem in Sweden, a Frenchman named Georges-Louis Leclerc was writing a
massive “natural history”—that is, an encyclopedia of all that was known
about the natural world at the time.
Like the philosophers of ancient Ionia, Leclerc suggested that all material
objects were composed of particles, and that in particular living organisms
were composed of “organic particles.” These could aggregate to form living
things and could also reaggregate to form other living things at other times.
This simple form of evolution was not far from that proposed by Lucretius,
but like those earlier theories, Leclerc’s was purely descriptive. He did not
suggest an actual mechanism for how such changes could come about, nor
did he suggest any way in which his ideas could be tested.
An aspect of Leclerc’s natural history that would be expanded later by sev-
eral geologists, and would eventually provide a crucial foundation for
Darwin’s theory of evolution, is that things that are happening now can be
assumed to have been happening in the past and to have produced the
world that we see around us today: “The present is the key to the past.”
This idea would by formalized into the principle of uniformitarianism, first
by the geologists James Hutton and later by Charles Lyell, who was to have
an extraordinarily important influence on the young Charles Darwin.
One of the intellectuals who had a profound, though often overlooked,
influence on subsequent developments was Erasmus Darwin, the grandfa-
ther of Charles Darwin. In 1803, Erasmus Darwin published a long prose-
poem entitled Zoonomia, or the Laws of Organic Life. In it, the elder
Darwin speculated on the origin of living things.
When Charles was working on the Origin of Species he considered using
some of his grandfather’s ideas in his own theory of evolution. However, he
eventually concluded that Erasmus Darwin’s ideas about “organic change”
owed more to the revolutionary temper of the times and could not be con-
sidered to be scientific.
As the director of the Musée National d’Histoire Naturelle, Leclerc
arranged to have fellow naturalist Jean-Baptiste Lamarck appointed as
curator of invertebrates.
Lamarck’s study of the mollusks of the Paris basin indicated that many
species had changed over time, with new species arising and others disap-
pearing. He summarized his ideas in his most important book, Philosophie
Zoologique, first published in 1809. In it, Lamarck presented the first logi-
cally reasoned scientific theory for the origin of species. He proposed two
laws, as follows:
• Use and disuse: “In every animal which has not passed the limit of
its development, a more frequent and continuous use of any organ
gradually strengthens, develops and enlarges that organ, and gives it
a power proportional to the length of time it has been so used;
33
 while the permanent disuse of any organ imperceptibly weakens
and deteriorates it, and progressively diminishes its functional
capacity, until it finally disappears.”
• Inheritance of acquired characteristics: “All the acquisitions or loss-
es wrought by nature on individuals, through the influence of the
environment in which their race has long been placed, and hence
through the influence of the predominant use or permanent disuse
of any organ; all these are preserved by reproduction to the new
individuals which arise, provided that the acquired modifications
are common to both sexes, or at least to the individuals which pro-
duce the young.”
• Lamarck also proposed that new living forms arose continuously
through a kind of spontaneous generation, so that independent lines
of evolving organisms are constantly being added to living systems.
A further aspect of Lamarck’s evolutionary theory, which Darwin would
directly oppose, was that as a result of their activities, species are constantly
“improving,” that is, becoming more complex and better adapted over time.
In other words, Lamarck believed that evolution had a purpose, which was
to produce more and more complex and highly adapted living organisms,
with the ultimate goal of bringing about the evolution of humans.
All the major features of Lamarck’s evolutionary theory have since been
shown to be either false or unnecessary for a scientific explanation of
evolutionary change. However, at the time, they were considered revolu-
tionary, and their importance to Darwin’s later theory has often been
ignored. Lamarck not only proposed that species could evolve; he was the
first to propose a law-like explanation for how such changes could take
place—explanations that could then be tested by empirical observation.
Unfortunately for Lamarck’s career, however, his ideas ran directly
counter to those of the most widely respected and politically powerful
naturalist in France: Georges Cuvier.
Jean Léopold Nicolas Frédéric Cuvier published his Discourse on the
Revolutionary Upheavals on the Surface of the Globe in 1825, proposing that
many species had gone extinct in the distant past as the result of worldwide
catastrophes. Cuvier’s ideas were extraordinarily influential and we will
briefly focus on four of them:
1. Extinction has happened. Cuvier believed in a version of deism in
which God intervened periodically in life on Earth by causing the cata-
strophes that resulted in mass extinctions. However, the idea that
extinction had occurred undermined a basic principle of Christian cre-
ationism: that God had created all forms of life all at once about 6,000
years ago and that since that time no significant changes have happened
to the originally created kinds. By legitimizing the idea of extinction
for scientists and undermining the concept of unchangeable “originally

34
 created kinds,” Cuvier unintentionally set the stage for Darwin’s theory
of evolution by natural selection.
2. Comparative anatomy can be used to show relationships between
extinct and still-living forms. Under the tenets of biblical creationism,
there are no necessary relationships between extinct and still-living
organisms. Indeed, the former are assumed for doctrinal reasons to be
impossible. Cuvier made it possible to believe that extinct organisms
were related to still-living ones, and that the way to explain those rela-
tionships was through the comparative study of the anatomy of extinct
and still-living forms. Darwin used these same principles in the Origin
of Species, but he proposed a revolutionary explanation for the relation-
ships both he and Cuvier had observed.
3. The history of life on Earth can be inferred from the fossils and other
remains in the layers of rock found around the world. According to the
most widespread interpretation of the biblical creation story, the fossils
and rock layers that Cuvier studied were deposited by a single world-
wide flood that happened only a few thousand years before and lasted
for only forty days and nights. However, as Cuvier pointed out, the
rapidly accumulating weight of the geological evidence was for multiple
extinction events, taking place over a very long period of time, and fol-
lowed each time by the repopulation of the world by new species of ani-
mals and plants.
4. The Earth must be very, very old. The age of the Earth according to the
biblical account is approximately 6,000 years. This is nowhere near
enough time for evolution to have occurred, and so even if it were pos-
sible for the “original created kinds” to have evolved (an idea rejected
by most biblical creationists), not enough time would have elapsed for
any significant evolutionary change to have happened.
The application of naturalistic explanations to the living world that was
begun by Lamarck and Cuvier reached its climax in the work of Charles
Darwin. His ideas have had an enormous impact on society, perhaps more
than those of any other single person. His books changed the world and
will continue to change it for the foreseeable future.
Darwin’s only formal training and his only formal academic degree was in
Anglican theology. How could he have written the most important book in
biology, if not all of science? There are several aspects of Darwin’s character
that could explain this apparent contradiction:
• He was an extraordinarily avid collector, especially of natural objects.
• He was very deeply interested in geology.
• He was fascinated by botany and “natural history.” His botany
teacher, Professor Henslow, thought so much of his talents that he
recommended that Darwin be appointed as ship’s naturalist for the

35
 voyage of HMS Beagle, a royal navy survey ship, scheduled for a
three-year around-the-world voyage.
The Beagle’s captain, Robert Fitzroy, felt that Darwin was insufficiently
qualified for the post, but he offered Darwin the position of “gentleman’s
companion.” While voyaging on the Beagle, Darwin read Charles Lyell’s
multivolume text, Principles of Geology, which convinced him of Lyell’s
principle of uniformitarianism.
From a reading of his journals and notebooks, it is clear that Darwin was
not convinced of the reality of evolution while on the voyage of the Beagle.
However, Darwin’s voyage aboard the Beagle transformed him from an
indifferent student to a passionate and highly skilled naturalist. He had a
natural talent for collecting specimens and recording his observations. He
wrote volumes of notes and sent thousands of specimens back to museums
in England. His notes eventually became the basis for his first book, A
Journal of the Voyages of HMS Beagle.
The crucial turning point in Darwin’s thinking came on the evening of 28
September 1838—two years after his return to England—when (according
to his autobiography),
. . . I happened to read for amusement “Malthus on Population,” and
being well prepared to appreciate the struggle for existence which
everywhere goes on from long-continued observation of the habits of
animals and plants, it at once struck me that under these circum-
stances favourable variations would tend to be preserved, and
unfavourable ones to be destroyed. The result of this would be the
formation of new species. Here then I had at last got a theory by
which to work . . .

36
 FOR GREATER UNDERSTANDING

Questions
1. Linnaeus, author of Systema Naturae, was a Christian creationist, yet his
work set the stage for Darwin’s theory of the origin of species. How and
why was this the case?
2. Which aspects of Lamarck’s theory of evolution did Darwin accept and
which ones did he deny and replace?
3. Why was Darwin so impressed with Reverend Paley’s books on natural
theology, and why did he eventually publish a book that undermined
Paley’s arguments?

Suggested Reading
Larson, Edward J. Evolution: The Remarkable History of a Scientific Theory.
New York: Modern Library, 2006.

Other Books of Interest

Ruse, Michael. The Darwinian Revolution: Science Red in Tooth and Claw.
Chicago: University of Chicago Press, 1979.
Thompson, Keith Stewart. Before Darwin: Reconciling God and Nature.
New Haven: Yale University Press, 2005.

Websites of Interest
1. Project Gutenberg provides the text of Erasmus Darwin’s Zoonomia, or
the Laws of Organic Life (1796). —
http://www.gutenberg.org/etext/15707
2. The Complete Work of Charles Darwin Online website features Charles
Darwin’s Journal of Researches into the Geology and Natural History of
the Various Countries Visited by HMS Beagle (1839). —
http://darwin-online.org.uk/EditorialIntroductions/
Freeman_JournalofResearches.html
3. The University of Colorado at Boulder’s Charles Darwin: Early
Evolutionists website provides Jean-Baptiste Lamarck’s Zoological
Philosophy (1809, reprinted in 1914). —
http://spot.colorado.edu/~friedmaw/Early_Evolution/Lamarck.html

37
Lecture 6
The Darwinian Manifesto: Natural Selection
The Suggested Reading for this lecture is Daniel C. Dennett’s Darwin’s
Dangerous Idea: Evolution and the Meanings of Life.

Most revolutions, including most scientific revolutions, begin with a mani-

festo of some sort. The opening salvo in the Darwinian revolutions was the
publication of Darwin’s most important (and controversial) book, the Origin
of Species, in 1859. In it, Darwin drew together the multiple threads of
nineteenth-century natural history and wove them into what he himself
called “one long argument.” Like any good argument, it was buttressed by
evidence, which Darwin marshaled to support his revolutionary (and deeply
disturbing) ideas.
But Darwin did not start out as a revolutionary. He was still a creationist
when, in 1836, he returned to England after the five-year voyage of the
Beagle. Upon his return, he pondered the things he had observed. In partic-
ular, he considered three sets of observations that were eventually to lead
him to the idea of evolution by natural selection:
1. The patterns he observed in the geographic distribution of animals and
plants as the Beagle circumnavigated South America. Darwin observed
that similar habitats in widely separated locations were inhabited by
similar (but not the same) species; he eventually concluded that this
indicated that such species had descended from common ancestors.
2. The fossils of extinct animals he observed and collected from all over
South America. His careful observations of these fossils convinced him
that they were the remains of species no longer present in South America,
but which were related to species that still existed. Like the geographical
distributions described above, these observations suggested that modern
species had descended from other, similar species now extinct.
3. The distribution of species he observed on volcanic islands in the
Atlantic and Pacific oceans. He noticed that although these islands were
located in the same types of habitat, they were inhabited by different
species. Furthermore, although these species were not at all related to
each other, they were related to species located on the nearby main-
land, suggesting again that the island species and the nearby mainland
species had descended from common ancestors.
According to Darwin, natural selection is the outcome of a process that has
four prerequisites:
1. Variety: There are significant variations in the characteristics of the
members of populations.

38
 2. Heredity: The distinct variations noted above must be heritable
from parents to offspring.
3. Fecundity: Living organisms have a tendency to produce more off-
spring than can possibly survive. Among those individuals that do
survive, those that also reproduce pass on to their offspring what-
ever heritable characteristics made it possible for them to survive
and reproduce.
4. Demography: Some individuals survive and reproduce more often
than others. Individuals survive and successfully reproduce because
of their physical and behavioral characteristics, which are the basis
for evolutionary adaptations.
In about 1854, Darwin began working on the manuscript of what he called
his “big species book,” to be titled Natural Selection. He toyed with the
idea of having it published after his death, so as to avoid the controversy
that he knew it would generate.
Darwin never published Natural Selection. Instead, he rushed a brief
“abstract” of his “big species book” into print in the fall of 1859. The rea-
son for this sudden rush to publication is well known: Darwin had been
scooped on his theory of natural selection by a fellow English naturalist,
Alfred Russell Wallace. Anxious to preserve his priority as the discoverer of
natural selection, Darwin rushed what he considered to be an “abstract” of
his ideas into print in November 1859. This “brief abstract,” published
without footnotes, illustrations, or bibliography, was the first edition of the
Origin of Species by Means of Natural Selection.
In it, Darwin began by pointing to the various breeds of domesticated ani-
mals and plants as being analogous to the products of natural selection. He
then launched into an extended discussion of domesticated pigeon breeds,
which he concluded are descendants of the wild rock dove.
Although these breeds are startlingly diverse, they are not separate
species. Darwin asserted that all seven-hundred-plus breeds of pigeons had
been bred from the wild rock dove by means of artificial selection and that
most of the artificial selection done by animal and plant breeders was prob-
ably done unconsciously, by breeders choosing desirable traits among their
domesticated animals and plants.
Darwin had two aims in writing the Origin of Species:
1. To convince his readers of the reality of “descent with modifica-
tion” from common ancestors; he was largely successful in this aim.
2. To convince his readers that natural selection was the cause of the
“beautiful adaptations” that define species; he was largely unsuc-
cessful in this aim.
To accomplish the second aim, Darwin was forced to use an “argument
from analogy,” because he could not point to any real-world examples. He

39
essentially argued that “breeds” under domestication are analogous to
“species” in the wild insofar as both are shaped by selection. The animal
and plant breeders that Darwin consulted believed that their breeds were
derived from separate species of pigeons in the wild. Darwin pointed out
that they were all derived from one “wild type” ancestor, which had been
modified by artificial selection. In other words, natural selection is analo-
gous to artificial selection.
After reading Malthus’s essay on population growth, Darwin realized that
the excess population growth that Malthus described would result in a
“struggle for existence” that he would later call “natural selection.”
Malthus’s Essay on the Principle of Population included two ideas that
were crucial for Darwin’s theory:
1. That the food supply in any area increases only linearly, whereas
the population increases exponentially.
2. That because of this every natural population will eventually out-
strip its food supply, leading to widespread starvation.
Darwin proposed that species in nature were subject to a “struggle for
existence” caused by the enormous reproductive potential of living organ-
isms. As Malthus pointed out, if a population is not limited by food, space,
or other resources, it will rapidly increase. In the Origin of Species, Darwin
pointed out that unchecked populations could easily cover the surface of
the Earth.
The “struggle for existence” proposed by Darwin is a struggle to leave the
most offspring, which over time will result in the offspring of the more
successful individuals becoming more common among the members of
their populations.
Central to Darwin’s theory was the idea that, contrary to the biblical
account of creation and history, the Earth was very old—indeed, many mil-
lions of years old. Darwin argued that natural selection acts too slowly to
be observed.
If this is the case, then how did Darwin go about proving to the reader
that natural selection occurs, and that it is the “engine” of “descent with
modification”? Darwin drew analogies to artificial selection in the breeding
of domesticated animals and plants. He also provided two examples of nat-
ural selection in action: wolves preying on deer, and plant-insect coevolu-
tion. However, it is important to note that both of these examples are imag-
inary. Darwin had no direct observable examples of natural selection.
Natural selection doesn’t depend upon survival alone. Indeed, only individ-
uals who reproduce pass on their heritable characteristics to their offspring.
This means that successful reproduction is at least as important, if not more
important, than survival alone. Darwin stated that mating among most ani-
mals is based on “female choice.” That is, females are “choosy” about who
they will mate with, while males are generally “ready and waiting” for
40
females to allow them to mate. Darwin pointed out that this will cause
females to shape the adaptations of males by choosing mates based on their
characteristics. He called this process sexual selection.
Darwin implied that sexual selection can have effects that are separate
from those due to natural selection (some evolutionary biologists agree,
but others argue that sexual selection is merely a special form of natural
selection). Darwin based most of his second-most-famous book, The
Descent of Man, and Selection in Relation to Sex, on the concept of sexual
selection, especially as the result of female choice. Darwin believed that
female choice could explain the evolution of the various races of humans,
as well as the more obvious differences between females and males in
other species.
Recall that according to Darwin, variation among the heritable characteris-
tics of individuals in populations is one of the most important prerequisites
for evolution.
Neither Darwin nor any of his contemporaries (that he knew of) had a
coherent theory of heredity or variation. In a coincidence of history,
Gregor Mendel had published his theory of heredity at about the same
time, but Darwin either never read it or didn’t understand its importance
to his own work. Consequently, Darwin could propose no theory of heredi-
ty or variation in the Origin of Species, nor could he suggest how it might
affect his conclusions.
However, instead of giving up his argument, he simply accepted as a given
that many important traits of animals and plants are heritable. He also pro-
posed that, although he had no explanation of how they arose, variations
among the members of a species do indeed occur and can provide the raw
material for natural selection.
Darwin also asserted that use and disuse could produce characteristics that
were inherited. This assertion is surprisingly close to that of Lamarck’s idea of
inheritance of acquired characteristics. Although Darwin returned to this idea
several times in the Origin, he concluded that such changes do not account
for most of the variation we observe among the members of most species.
Criticisms
Darwin’s imagination (and his faith in natural selection alone) sometimes
seemed to fail him. Speaking of blind cave fish, he wrote:
[It] is difficult to imagine that eyes, though useless, could be in any
way injurious to animals living in darkness, I attribute their loss
wholly to disuse.
Actually, it is relatively easy to explain the evolution by natural selection
of eyelessness in cave fish. Eyes, especially those of fish (which have no
eyelids) are a common site of infection and injury. Natural selection is
essentially a balance between positive and negative aspects of any trait.

41
If the positive aspects outweigh the negative, the trait will persist; other-
wise it will eventually disappear. In the case of eyes, as long as the positive
benefit of sight outweighs the probability of infection or injury, eyes will
persist. However, without any positive benefit from having eyes, natural
selection will eventually cause their disappearance.
Darwin also stressed that “correlation of growth” could produce peculiar
side effects when only certain traits were subjected to selection.
Selection for traits controlled by genes that have more than one phenotyp-
ic effect can produce considerable variation between the individuals in pop-
ulations, which may serve as raw material for selection. Darwin seemed to
be asserting that because of correlation of growth, there are limits on how
much change can take place in any organism (or part of an organism) as the
result of natural selection. However, later in the same chapter he wrote:
I believe . . . natural selection will always succeed in the long run in
reducing and saving every part of the organization . . . without by
any means causing some other part to be largely developed in a corre-
sponding degree. And, conversely, that natural selection may perfectly
well succeed in largely developing any organ, without requiring as a
necessary compensation the reduction of some adjoining part.
As he stated in both the Origin of Species and his autobiography, Darwin
used a powerful technique to deal with his critics: he listened very carefully
to their criticisms and objections and addressed these directly in his presen-
tations of his theories. For example, he anticipated that some readers would
disbelieve his assertion that the wings of bats are descended from a com-
mon ancestor of the hands of humans. He countered this by pointing out
that it is possible to imagine how bats might have evolved from something
like a flying squirrel.
In so doing, Darwin committed a serious fallacy: implying that a species
living today is descended from another species living today. Creationists
gleefully jump on such assertions, because they are in nearly all cases egre-
giously false. What Darwin should have said is that flying squirrels and bats
are both descended from a squirrel-like common ancestor.
Darwin pointed out that convergent evolution (that is, adaptation to simi-
lar environmental pressures) could result in traits that appeared very similar
in unrelated organisms. This could lead observers to false assumptions
about common ancestry and phylogenetic lineages. He suggested that it
would be more useful to focus attention on nonadaptive characteristics,
especially when determining phylogenetic relationships (that is, construct-
ing evolutionary “family trees” of descent with modification).
Darwin concluded that evolution, like all of nature, does not act by sud-
den jumps. However, as we will see later in this series of lectures, on this
point at least, one hundred fifty years of paleontology have tended to point
to a very different conclusion.

42
 Many of Darwin’s critics pointed out the inconceivability of the idea that
an organ such as the vertebrate eye, so complex and well-adapted, could
have arisen without some kind of design or purpose in mind. Darwin coun-
tered this argument—often referred to as an “argument from incredulity”—
by pointing out that it is possible to imagine how such an organ arose, not
from a sudden creation, but rather from a series of gradual steps.
Darwin therefore asserted the following:
If it could be demonstrated that any complex organ existed, which
could not possibly have been formed by numerous, successive, slight
modifications, my theory would absolutely break down. But I can find
out no such case.
Darwin himself pointed out another potential fatal argument against his
theory: if any species could be shown to have evolved a trait exclusively for
the benefit of another species, it could not have done so by natural selec-
tion. The only logical alternative is design by a benevolent deity. Darwin
pointed out that in many cases, what seem to be adaptations that benefit
other species (such as the flowers that provide nectar and excess pollen to
pollinating insects) actually benefit both species, and so natural selection is
not undermined. Indeed, Darwin took pains several times in the Origin to
point out that natural selection generally results in adaptations that are far
less than perfect. His point in doing so was to imply that an omnipotent
supernatural creator would not have created such “imperfect adaptations.”
Darwin was very interested in the behaviors of nonhuman animals, espe-
cially those that were commonly referred to as “instincts.” He analyzed
instinctive behaviors in much the same way as he wrote about the anatomi-
cal characteristics of organisms:
The canon of Natura non facit saltum applies with almost equal force
to instincts as to bodily organs.
He then launched into a discussion of the evolution of the fascinating
behavior of two groups of social insects: honey bees and ants.
Thus, as I believe, the most wonderful of all known instincts, that of
the hive-bee, can be explained by natural selection having taken advan-
tage of numerous, successive, slight modifications of simpler instincts.
But then, immediately following this statement, Darwin pointed out that
the existence of sterile castes in social insects could present a “fatal flaw to
the theory” of evolution if he could not explain them as just another case of
natural selection in action.
Members of neuter castes (such as “worker ants”) have instincts and
anatomical features that are different from those of reproductive individuals
(such as “queen ants”). The question Darwin confronted was, how can a
characteristic of a neuter (that is, sterile) individual be passed on?

43
 Darwin answered:
This difficulty, though appearing insuperable, is lessened, or, as I
believe, disappears, when it is remembered that selection may be
applied to the family, as well as to the individual, and may thus gain
the desired end.
Darwin’s argument was this:
• Neuter castes show adaptive variation, just like individual organisms.
• Neuter caste members are directly (and closely) related to reproduc-
tive individuals.
• Therefore, selection acting on fertile individuals can produce adap-
tations in their closely related sterile “family members.”

44
 FOR GREATER UNDERSTANDING

Questions
1. What was it about Darwin’s theory of evolution by natural selection that
made it convincing for scientists in a way that Lamarck’s theory was not?
2. What is the importance of variation to Darwin’s theory of natural selection?
3. The prevailing theory of inheritance at the time of Darwin’s Origin
was that the characteristics of living organisms were blended during
mating, like different colors of paint. If this were the case, would
Darwin’s theory of natural selection be viable?

Suggested Reading
Dennett, Daniel C. Darwin’s Dangerous Idea: Evolution and the Meanings
of Life. New York: Simon & Schuster, 1996.

Other Books of Interest

Futuyma, Douglas. Evolution. 2nd ed. Sunderland, MA: Sinauer
Associates, 2009.
Larson, Edward J. Evolution: The Remarkable History of a Scientific Theory.
New York: Modern Library, 2006.
Zimmer, Carl. Evolution: The Triumph of an Idea. New York: Harper
Perennial, 2006.

Websites of Interest
The Complete Work of Charles Darwin Online website features Charles
Darwin’s On the Origin of Species by Means of Natural Selection, or the
Preservation of Favoured Races in the Struggle for Life (1859). —
http://darwin-online.org.uk/content/frameset?itemID=
F373&viewtype=side&pageseq=1

45
Lecture 7
The Darwinian Manifesto: Descent with Modification
The Suggested Reading for this lecture is Daniel C. Dennett’s Darwin’s
Dangerous Idea: Evolution and the Meanings of Life.

Darwin included an entire chapter on hybridization in the Origin of

Species. This is because the theory of special creation, which Darwin
directly opposed, implies that species are created separately and that there
are “unbreakable barriers” between species that prevent real hybridization.
Darwin attacked this idea on three fronts:
1. He pointed out that there are viable hybrids between many species
in nature, thereby undermining the “unbreakable barrier” argument.
2. He also pointed out that natural selection itself could not erect any
such barriers, because natural selection cannot possibly select for
any form of sterility. How can a tendency toward sterility possibly
be inherited?
3. Finally, he pointed out that within species there is nearly as much
sterility as exists between species. This implies that sterility per se
is neither a necessary nor a sufficient condition for defining species,
nor does it necessarily imply anything about the supposedly
“unbreakable” barriers between species.
Darwin asserted that hybrid sterility or inviability must be side effects of
the divergence of species. Essentially, once one species has diverged into
two separate species, random changes in the hereditary makeup of the
members of the separate species will eventually result in their being unable
to interbreed and produce viable offspring.
The Fossil Record
During the late seventeenth and early eighteenth centuries, geologists cod-
ified several principles that correlated rock formations with the passage of
time and distribution in space. These principles are the basis for the sci-
ence of stratigraphy, which is the study of the pattern of layering in sedi-
mentary rocks.
The principles of stratigraphy, when combined with Lyell’s principle of uni-
formitarianism, implied that the Earth was much older than the biblical
account of creation. Geologists and evolutionary biologists have used sever-
al techniques to provide dates for geological processes:
• Relative dating: Relative dates are usually based on stratigraphic
position; that is, deeper strata are considered older, whereas more
superficial strata are considered newer (that is, more recently
deposited). Fossil inclusions are very often used to identify and

46
 correlate stratigraphic sequences, and as a consequence are central
to the process of relative dating.
• Absolute dating: Several techniques have been developed to allow
geologists to infer absolute (that is, chronological) dates for different
rock layers. Each of these techniques depends upon a physical or
chemical process that changes over a known rate of time, such as
the decay of radioactive isotopes in igneous rock intrusions.
Relative and absolute dating scales have been combined to produce the
geological time scale. The order of layers in this column (which are general-
ly named after the geographical region from which they were first
described) are the same the world over, although the entire column is not
known from any single location. There are very large gaps in most of these
layers, and in many places whole layers are entirely missing.
Darwin described this situation by saying that the fossil record (the collec-
tion of fossils that might confirm the theory of evolution) is everywhere
incomplete. We do not have a continuous, unbroken fossil record of the
evolution of any living thing, and certainly not for life on Earth as a whole.
In particular, Darwin pointed out that intermediate forms are almost
entirely missing from the fossil record. He wrote that this is to be expected,
for two reasons:
1. The process of natural selection itself generally eliminates the interme-
diate forms, as the more recent forms are better adapted and have
replaced the older ones.
2. There is a very low probability of finding a complete record, plus the
difficulty of finding a transitional form among all of the other forms in
the geological column.
That was the situation in Darwin’s time. Today, we have the opposite prob-
lem: There are literally millions of fossils in collections around the world,
most of which have never been carefully analyzed.
The geographical distribution of animals and plants around the world pro-
vided Darwin with a powerful argument against the theory of special cre-
ation: Why would a deity create unrelated, but very similar, organisms at
the same latitude but on different continents, when they had the same cli-
mate, geology, and so forth, but create different, yet closely related, organ-
isms at the same latitude on the same continents?
Darwin pointed out that if one travels up or down the coast of nearly any
continent, one “never fails to be struck by the manner in which successive
groups of beings, specifically distinct, yet clearly related, replace each other.”
Finally, Darwin pointed out that the inhabitants of islands lying at about the
same latitudes worldwide were also populated by animals and plants that
were not at all related to each other. Instead, they were closely related to
organisms located on the nearby mainland, providing strong evidence that

47
they had been derived from those organisms, rather than having been creat-
ed in place. Taken together, these correlations present some of the strongest
evidence for descent with modification and were crucial to Darwin’s eventu-
al success in convincing most biologists that evolution had happened.
The distribution of several species of fossil animals and plants at the end of
the Permian period (approximately 245 million years ago) was puzzling to
Darwin. Fossils of extinct animals and plants, such as Cynognathus,
Lystrosaurus, and Glossopteris from South America, Africa, India, and
Australia, were similar enough to be classified in the same species (or at
least the same genus). Yet, they were so widely separated as to require
Darwin to propose complex explanations, such as land bridges and
transoceanic floating mats of vegetation.
Now we know that these fossils are explainable with reference to a much
broader explanation. All of the continents (including Antarctica) were once
connected in a giant continent, called Pangea, which later split apart into
six pieces and “drifted” to their current locations. The theory of continental
drift (with its underlying geological theory, called plate tectonics) provides
the explanation that Darwin missed.
There is also very strong evidence that sudden, drastic changes can alter
not only the course of evolution, but the geological features of the Earth
itself. For example, there is increasing evidence that the extinction of
the dinosaurs at the end of the Cretaceous period was caused by an
asteroid collision.
Darwin completely overturned the previous system of taxonomy, which
was based on the underlying assumption that all living things had been cre-
ated by God in essentially their present form, and that species boundaries
were fixed and unbreakable.
Darwin proposed descent as the basis for a more “scientific” systematic
classification and pointed out that basing a new system of classification on
descent (that is, evolution) was prone to error in the case of convergent
organisms (that is, organisms that appear superficially similar as the result
of adaptation to similar environmental conditions).
This caveat has caused problems for systematists right up to the present
day. An important point to note in this context is that acceptance of natural
selection as the primary “engine” of evolutionary descent is not necessary
for the construction of a taxonomy based on descent. On the contrary, evo-
lutionary systematics is concerned only with the outcome of evolution, not
with its mechanism.
For this reason, and to compensate for the pitfalls of convergent adapta-
tions, systematists have generally followed Darwin’s lead and used non-
adaptive characters as the basis for taxonomic groupings.
Systems of evolutionary classification are often confounded because of con-
fusion between homology and analogy. Homology (in evolutionary biology)

48
is the existence of similar (or modified) characteristics as the result of
descent from a common ancestor. Examples of homology are the wings of
bats and the hands of humans. Although these structures appear quite dif-
ferent at first glance, a more detailed examination of the bone structure of
both indicates that the same bones are located in the same relationships
with each other.
Analogy (in evolutionary biology) is the existence of similar characteristics
as the result of convergent evolution. Examples of analogy are the wings of
insects and the wings of birds. They both appear superficially similar in
some respects, and both perform the same functions for the animals that
have them, but they are not derived from a common ancestor. That is, the
common ancestor of insects and birds (a very primitive animal indeed) did
not have wings, which evolved independently in insects and birds.
Recent genetic analysis of many structures in many species of animals has
indicated that what were once thought to be the result of homology actually
are not; in many cases, structures that appear to have been derived from a
common ancestor actually evolved independently in separate lines of descent.
There are several objections that have been raised to the use of evolution-
ary descent as the basis for a comprehensive system of taxonomic classifica-
tion. Beside the obvious objections of creationists, there are some problems
with using descent for classification, even among scientists.
The prevailing “biological species concept” (which is based on the ability
of members of the same species to interbreed and produce fertile off-
spring under natural conditions) is not applicable to several important
groups of organisms:
• Extinct organisms (known only from fossils or preserved specimens)
• Organisms whose reproductive capacity in the wild is unknown
• Organisms that can be forced to hybridize under laboratory condi-
tions, but do not do so under natural conditions
• Asexually reproducing organisms
Evidence of descent with modification from common ancestors is useful in
applying the currently most favored kind of classification scheme, called
cladistics. Cladistics is a system of classification based on shared derived
characteristics (that is, characteristics that have changed over time and are
therefore shared by the descendants of a common ancestor).
The remarkable complexity and similarity of the embryos of widely separated
vertebrate groups (such as fish, amphibians, reptiles, birds, and mammals),
plus the tendency of developing embryos to survive rather drastic shocks
without lasting damage, has often been cited as evidence of intelligent design.
However, Darwin pointed out that these same similarities could be viewed as
evidence for descent with modification from common ancestors sharing simi-
lar early embryonic stages.

49
 Several qualities of the Origin made its reception by scientists and lay
people alike controversial:
• Only blind and purposeless natural forces (that is, heredity, varia-
tion, and natural selection) were needed to explain the extraordi-
nary diversity and adaptive perfection of living systems.
• There was no reference to supernatural forces whatsoever, especial-
ly in the first edition of the Origin.
• Darwin implied (but did not explicitly state) that humans had
evolved from lower forms of life.
• The diversity of living organisms was explained as the result of
descent with modification (Darwin’s term for “evolution”), which
Darwin suggested could be used to extensively revise the taxonomy
of life on Earth.
• Natural selection doesn’t, and almost certainly can’t, produce per-
fect adaptations. All adaptations are, of necessity, compromises.
• Natural selection, in the long run, virtually guarantees extinction.
Indeed, the more “perfectly adapted” a species is to its environ-
ment, the more likely it is to go extinct if that environment
changes significantly.
• Life almost certainly arose on Earth only once; since then, all living
organisms are the descendants of that most ancient of ancestors.
Darwin concluded the Origin with these paragraphs:
It is interesting to contemplate an entangled bank, clothed with many
plants of many kinds, with birds singing on the bushes, with various
insects flitting about, and with worms crawling through the damp
earth, and to reflect that these elaborately constructed forms, so dif-
ferent from each other, and dependent on each other in so complex a
manner, have all been produced by laws acting around us.
Thus, from the war of nature, from famine and death, the most exalt-
ed object which we are capable of conceiving, namely, the production
of the higher animals, directly follows. There is grandeur in this view
of life, with its several powers, having been originally breathed into a
few forms or into one; and that, whilst this planet has gone cycling
on according to the fixed law of gravity, from so simple a beginning
endless forms most beautiful and most wonderful have been, and are
being, evolved.

50
 FOR GREATER UNDERSTANDING

Questions
1. Why was the question of hybridism crucial to Darwin’s theory of descent
with modification?
2. What does the fossil record show us about the pattern of evolution over
time, and how do we know?
3. Darwin’s arguments for the biogeographic distribution of species around
the world have never been directly addressed by creationists. Why is this,
and why do most evolutionary biologists consider that Darwin’s argu-
ments for biogeographical distribution constitute his strongest argument
for descent with modification (and against creationism)?

Suggested Reading
Dennett, Daniel C. Darwin’s Dangerous Idea: Evolution and the Meanings
of Life. New York: Simon & Schuster, 1996.

Other Books of Interest

Futuyma, Douglas. Evolution. 2nd ed. Sunderland, MA: Sinauer
Associates, 2009.
Larson, Edward J. Evolution: The Remarkable History of a Scientific Theory.
New York: Modern Library, 2006.
Zimmer, Carl. Evolution: The Triumph of an Idea. New York: Harper
Perennial, 2006.

Websites of Interest
The Complete Work of Charles Darwin Online website features Charles
Darwin’s On the Origin of Species by Means of Natural Selection, or the
Preservation of Favoured Races in the Struggle for Life (1859). —
http://darwin-online.org.uk/content/frameset?itemID=
F373&viewtype=side&pageseq=1

51
Lecture 8
Mendel’s Dangerous Idea
The Suggested Reading for this lecture is Peter J. Bowler’s The Eclipse
of Darwinism: Anti-Darwinian Evolution Theories in the Decades
Around 1900.
Darwin began his summary of his views on variation with this statement:
Our ignorance of the laws of variation is profound.
Neither Darwin nor any of his contemporaries (that he knew of) had a
coherent theory of heredity or variation. However, this was not an insuper-
able obstacle to Darwin. Instead of giving up his argument, he simply
accepted as a given that many important traits of animals and plants are
heritable, pointing to the observable facts of inheritance in domesticated
animals and plants. He also proposed that, although he had no explanation
of how they arose, variations among the members of a species do indeed
occur and can provide the raw material for natural selection.
This tactic on Darwin’s part was largely successful, for a while. His asser-
tion that the huge diversity of living forms and their exquisite adaptations
had evolved by “descent with modification from common ancestors” was
largely accepted by his scientific contemporaries. However, his assertion
that natural selection was the mechanism by which this process had
occurred was not nearly as widely accepted.
There were two reasons for this lack of acceptance:
1. Many of Darwin’s contemporaries (and, in fact, Darwin himself)
believed in Lamarck’s assertion that acquired characteristics could
be inherited. This process directly contradicts the blind and pur-
poseless process of natural selection, and therefore “holds the door
open” for purpose in evolution.
2. The consensus among naturalists was that inheritance worked by
“blending” the characteristics of parents, which would cause any
incipient adaptations to be diluted out of existence.
This second objection was in many ways the more worrisome to Darwin. In
an influential review of the Origin, Fleeming Jenkin in 1867 pointed out that
blending inheritance would eliminate variation within a few generations.
The variations that provide the raw material for natural selection must be
“real”—that is, they must have significant effects on survival and reproduc-
tion, and they must persist from one generation to the next. However, if all
traits are blended from generation to generation, all of the distinctiveness of
each variation would be lost and the population would remain essentially
unchanged in the long run. This was what most naturalists of Darwin’s time
believed. Darwin got around this objection by proposing that large numbers

52
of new variations (what we would now call “mutations”) occur with each
new generation. He called these changes “continuous variations” and even-
tually proposed a theory of genetic inheritance called pangenesis.
In The Variation of Animals and Plants Under Domestication (1868),
Darwin proposed that all of the traits of organisms produced “particles” of
inheritance, called “pangenes,” which could travel from the anatomical
locations of the traits to the sex cells, where they could be passed on to the
organism’s offspring. He proposed that the pangenes would probably travel
through the circulatory system and that they could somehow enter the sex
cells in the gonads prior to mating and reproduction.
The problem was that neither of these assertions matched what naturalists
observed. The amount of variation that appeared with each generation,
while significant, was not sufficient to explain why such variations would
not eventually disappear as they were blended with other traits.
Furthermore, Darwin’s “pangenes” could not be detected, only inferred,
nor could their observable effects be separated from the effects predicted by
the theory of blending inheritance (not to mention that they would produce
a form of inheritance indistinguishable from Lamarck’s inheritance of
acquired characteristics). Several experiments by Darwin’s contemporaries
produced results that contradicted Darwin’s theory, and consequently it was
not widely accepted, even by his closest colleagues. Therefore, although
most naturalists accepted that descent with modification had occurred, they
did not agree that it had occurred by natural selection.
At about the same time that Darwin was working out his ideas on natural
selection and evolution, an Augustinian monk named Gregor Mendel was
working out a revolutionary new theory of genetics.
Mendel observed that some offspring of some organisms had traits that
were similar to only one parent, rather than being intermediate between
both. He explained this phenomenon by assuming that heredity was deter-
mined by tiny, indivisible bodies that were passed from the parents to the
offspring via the reproductive cells. This would explain how some traits
could remain unblended in the next generation.
In his most famous set of experiments, Mendel studied twenty-two vari-
eties of pea plants of the same species (Pisum sativum). He studied a total
of seven different traits:
1. Seed shape. 5. Unripe pod color.
2. Seed color. 6. Flower position on the stem.
3. Seed coat color. 7. Stem height.
4. Ripe pod shape.
Mendel always began with plants that were true-breeding. That is, the
forms of each trait were passed from parent to offspring without significant
changes. Mendel then performed a series of controlled fertilizations, which

53
geneticists and plant breeders call crosses. Some of these crosses were self-
crosses, that is, fertilization of a plant using its own pollen. Other crosses
were cross-fertilizations—fertilization using pollen from another plant. In
each cross-fertilization, Mendel placed pollen from specific individual plants
on the egg-containing parts of specific individual plants.
Consider Mendel’s results for seed shape. Mendel took pollen from plants
that produced smooth seeds and fertilized the flowers of plants that pro-
duced wrinkled seeds. He also did the reciprocal cross, taking pollen from
plants that produced wrinkled seeds and fertilizing the flowers of plants
that produced smooth seeds.
The original true-breeding plants were the parental generation. The off-
spring obtained from a cross are called the first filial generation (usually
referred to as the F1 generation). All of the F1 seeds obtained from this cross
were smooth, regardless of which plant provided the egg and which plant
provided the pollen. Notice that this means that the characteristics of the
two parents were not blended in the F1 generation. Rather, one of the two
characteristics—in this case smooth seeds—completely masked the other
characteristic (that is, wrinkled seeds).
In the next growing season, Mendel planted the smooth seeds obtained
from the first cross. He then allowed the plants produced from these F1
seeds to self-fertilize, producing the second filial generation (usually
referred to as the F2 generation). Because these plants were self-fertilized,
this was essentially a cross between two smooth-seeded F1 plants. Such a
cross appears to be a cross between two true-breeding individuals, which
most breeders at the time would probably assume would produce an F2 gen-
eration in which all the pea plants also had smooth seeds.
But this isn’t what happened. Instead, in this F2 generation, Mendel
obtained 5,474 plants that yielded smooth seeds and 1,850 plants that yield-
ed wrinkled seeds. The trait of wrinkled seeds had disappeared for one gen-
eration (the F1) but had reappeared unblended in the next generation (the
F2). To most plant breeders at the time, this outcome would have seemed
outlandish, even annoying. But to Mendel, it confirmed his theory of
unblending “particulate” inheritance.
In his other experiments investigating the inheritance of the other six
traits, Mendel recorded similar proportions in all of the F2 generations. In
every case, the F2 offspring were distributed in approximately a 3:1 ratio.
Clearly, the two forms of these traits did not blend with each other, and so
Mendel’s hypothesis concerning particulate inheritance was verified. On
the basis of the numerical analysis of his results, he concluded that discrete
units of heredity are transferred unblended from parent to offspring.
Mendel explained this result by saying that the lost form of each trait was
actually latent or “masked” by the expressed form. He called the prevailing
form of a trait “dominant” and the latent form of a trait “recessive.”

54
Mendel’s definitions of dominance and recessiveness are sometimes called
Mendel’s law of dominance.
In the example just considered, the gene for seed shape has two different
forms. One form—the dominant form—produces smooth seeds. The other
form—the recessive form—produces wrinkled seeds. Different gene forms
that produce different forms of a trait are called alleles.
Following Mendel’s lead, geneticists observe an organism’s phenotype, the
physical appearance of an organism that is the result of the way in which
its genes are expressed. For example, the phenotype of our pea plant would
be described as having smooth seeds.
Most large organisms, including nearly all plants, have two sets of genetic
material, one set received from each parent during fertilization. Therefore,
such organisms can have two alleles for each gene. If the two alleles are the
same (whether dominant or recessive), then the organism is said to be
homozygous for that gene. If the two alleles are different, then the organ-
ism is heterozygous, and the dominant allele determines the phenotypic
expression of that gene by masking the expression of the recessive allele.
Mendel could not observe directly whether a pea plant was homozygous
dominant, homozygous recessive, or heterozygous for any of the traits he
was studying. He could only infer the pea plants’ genotype, the underlying
set of alleles that produced the organism’s phenotype. An organism’s geno-
type consists of all of its alleles. The effects of dominant alleles are usually
visible in the phenotype. However, the effects of recessive alleles are
expressed only when no dominant alleles for that trait are present, a condi-
tion usually referred to as homozygous recessive.
Mendel observed that dominant and recessive forms of a trait did not
become blended. Instead, the recessive form of the trait reappeared in an
unaltered form in the F2 generation. Based on this observation, Mendel for-
mulated his law of segregation, which states that the different forms of a
trait remain separate and unblended from generation to generation.
A shorthand technique for predicting the outcomes of genetic crosses,
developed by the English geneticist R.C. Punnett, is the Punnett square
method. In this method, the alleles of one parent are listed down the left
side of a two-by-two matrix (a “Punnett square”), and the alleles of the
other parent are listed across the top of the two-by-two matrix. The geno-
types of the fertilized zygotes that can result from the combining of these
alleles are indicated within the four cells of the Punnett square.
Because Mendel’s major work was done with garden peas, which exhibit
simple patterns of inheritance, Mendel could clearly and convincingly vali-
date his hypothesis concerning the units of heredity. Indeed, he was so con-
vinced of the validity of his conclusions that his subsequent work with other
plants, some of which failed to support his hypothesis, did not discourage
him. He persisted in his studies, although his contemporaries believed in a

55
completely different theory of inheritance. Understanding how inheritance
works and seeing that it could be explained by a few simple mathematical
laws was sufficient for him.
Mendel’s belief that his work would eventually be recognized was not mis-
taken. In 1900, only fourteen years after his death, his work was simultane-
ously rediscovered by three different geneticists—Carl Correns, Erich
Tschermak, and Hugo de Vries—working independently in three different
countries. They each realized that Mendel’s particulate theory of inheri-
tance fit the patterns of inheritance they were observing in the organisms
they were studying.
It is interesting to speculate what Darwin would have thought had he
known about Mendel’s work. Genes that did not blend in each generation
were the answer to Darwin’s dilemma and could have put him onto the
right track as early as 1866, the year Mendel’s most important paper was
published. A copy of the journal containing Mendel’s paper was found in
Darwin’s library at Down House, but it had not been opened or read.
There is an even deeper irony: the rediscovery of Mendel’s work led
geneticists to reject natural selection as the mechanism for evolution, in
favor of mutations. Hugo de Vries, one of the rediscoverers of Mendel’s
work, proposed that “mutations” (that is, changes in the phenotype of an
organism, occurring in just one generation) were the primary “engine” of
evolutionary change, not natural selection.
De Vries did his pioneering work in genetics studying the evening primrose
(Oenothera biennis), which is known for having sudden, large mutations in
its overall phenotype. De Vries argued that these kinds of mutations were
the basis for the changes in phenotype to which Darwin referred in the
Origin of Species, and that therefore natural selection was neither necessary
nor likely as a cause of evolutionary change. So convinced was de Vries that
the mutant forms of primrose constituted a new species arising from muta-
tion alone that he proposed a new scientific name for them, classifying them
as Oenothera lamarkiana, in honor of Jean-Baptiste Lamarck (and, perhaps,
in a not-so-subtle dismissal of Darwin).
By the turn of the twentieth century, the rise of what is now called
Mendelian genetics seemed to have completely replaced Darwin’s theory
of evolution by natural selection—not that evolution itself had been under-
mined. On the contrary, de Vries and the other Mendelian geneticists firm-
ly believed in radical, fundamental change in the underlying genetic char-
acteristics of living organisms by means of sudden genetic mutations. What
they believed they had proven false and replaced was Darwin’s proposed
mechanism of evolution, natural selection. In the Origin of Species,
Darwin had made it very clear that the kinds of changes he envisioned as
the basis of natural selection were so slight as to be almost unnoticeable.
Darwin wrote several times in the Origin that “nature does not make

56
jumps,” by which he clearly meant that evolutionary change was gradual,
not sudden.
The early Mendelian geneticists did not agree. Their analysis, which they
took directly from Mendel, indicated that the traits of living organisms were
discrete and unblending and appeared all at once in a single generation. In
1894, William Bateson, one of the founders of Mendelian genetics in
England and coiner of the term “genetics,” published a huge compendium
of such “sudden” mutations. Entitled Materials for the Study of Variation:
Treated with Especial Regard to Discontinuity in the Origin of Species, it
was a copiously illustrated encyclopedia of peculiar, even bizarre, muta-
tions, from whales with legs to flowers like something out of a fever dream,
all illustrated in living black and white.
The new geneticists, using Mendel’s revolutionary theory of inheritance,
were on the march, clearing the way to an entirely new view of the origin
and evolution of the characteristics of living organisms. So convincing was
their mathematical and empirical theory of inheritance that the mutational
theory of evolution was accepted by most prominent geneticists at the turn
of the century, which led to multiple public testimonials that “Darwinism
was dead.” But, as will be seen, the reports of the death of Darwinism
were greatly exaggerated.

57
 FOR GREATER UNDERSTANDING

Questions
1. Why did many of Darwin’s contemporaries reject his theory of natural
selection, while retaining his theory of descent with modification?
2. Why is it likely that Mendel’s training in Newtonian physics was important
in his development of the theory of unblending “particulate” inheritance?
3. Why did their research into the genetics of mutations lead the early
Mendelian geneticists to reject Darwin’s mechanism of natural selection
in favor of the origin of species by means of genetic mutations?

Suggested Reading
Bowler, Peter J. The Eclipse of Darwinism: Anti-Darwinian Evolution
Theories in the Decades Around 1900. Baltimore: The Johns Hopkins
University Press, 1992 (1983).

Recorded Books
Dyer, Betsey Dexter. The Basics of Genetics. The Modern Scholar Series.
Prince Frederick, MD: Recorded Books, LLC, 2009.

Websites of Interest
1. The Internet Archive website provides William Bateson’s Materials for
the Study of Variation: Treated with Especial Regard to Discontinuity in
the Origin of Species (1894). —
http://www.archive.org/stream/materialsforstud00bate/
materialsforstud00bate_djvu.txt
2. The Complete Work of Charles Darwin Online website features Charles
Darwin’s The Variation of Animals and Plants Under Domestication
(1868). — http://darwin-online.org.uk/content/frameset?itemID=
F880.1&viewtype=side&pageseq=1
3. The Christ’s College Cambridge (UK) Charles Darwin & Evolution web-
site provides an article entitled “The Eclipse of Darwin.” —
http://www.christs.cam.ac.uk/darwin200/pages/index.php?page_id=f2

58
Lecture 9
Equilibrium Violated: The Hardy-Weinberg Law
The Suggested Reading for this lecture is William B. Provine’s The Origins of
Theoretical Population Genetics, chapter 5, “Mathematical Consequences of
Mendelian Heredity.”

Darwin’s theory of evolution by natural selection was truly revolutionary

and represented a fundamental break from the ancient tradition of natural
history. That tradition, which can be traced back over twenty centuries to
the Greek philosopher Aristotle, had as one of its central concepts the idea
of design and purpose in nature.
What made Darwin’s theory so revolutionary was that it explained the origin
of species and of adaptations without reference to any design or purpose in
nature. Darwin proposed that there are a set of natural laws that bring about
objects and processes in living organisms without anyone or anything neces-
sarily intending that they do so. Just as a dropped rock falls to the ground
because of the physical law of gravity (but not “in order to” reach the
ground), living organisms have the characteristics that they have because of
what could be called the law of evolution by natural selection.
Darwin didn’t call his revolutionary explanation the “law” of evolution for
historical and philosophical reasons. During the first few centuries of the
Scientific Revolution, the explanations that were formulated to describe and
predict the behavior of physical and chemical processes were usually
referred to as “laws of nature.” However, by the time Darwin wrote the
Origin of Species, the term “law” had come to be replaced in many uses by
the word “theory.” As learned, scientific theories are explanations for
observable natural phenomena that have been thoroughly tested and for
which no invalidating evidence has yet been observed. According to the sci-
entific use of these terms, a “theory” is much broader and more compre-
hensive than a law, and in general has much more observational and exper-
imental evidence supporting it. And, in most cases, a scientific theory has
an underlying mathematical form, which can often be succinctly stated in
the form of a mathematical equation or set of related equations.
Furthermore, virtually all scientists agree that natural phenomena can, and
therefore should, be completely understood and explained simply by refer-
ring to other natural objects and processes, without reference to supernat-
ural entities or forces, and without requiring that there be any design or
purpose in nature. These criteria, which are often referred to as the princi-
ples of “methodological naturalism,” were generally not a part of natural
history until Darwin proposed his theory of evolution by natural selection.
For this reason, most historians of science agree that Darwin’s theory was
the first and most important step in the reformulation of “natural history”
as the science of biology.
59
 But what about the commonly accepted criterion that a comprehensive sci-
entific theory must be formulated in the language of mathematics?
Although Darwin’s theory was clearly formulated according to the princi-
ples of methodological naturalism, it just as clearly was not formulated in
explicitly mathematical terms. Darwin’s argument was essentially logical
and empirical, not mathematical. He asserted that there were four precon-
ditions for natural selection—variety, heredity, fecundity, and demogra-
phy—and that if these four preconditions are met, there is an inevitable
outcome: the heritable characteristics of those individuals who survive and
reproduce more often than other individuals with different characteristics
will become more common in their populations over time. One can easily
imagine that a mathematical reformulation of these conditions might be
possible—indeed, Darwin himself thought so. However, Darwin was (by his
own rueful admission) not a mathematician, nor were most of his contem-
porary supporters.
This situation changed dramatically with the rediscovery of Mendel’s laws
of genetic inheritance and the rise of the new science of genetics. Mendel
himself was trained as a physicist, and his theories were explicitly mathe-
matical in form. Mendel’s laws of segregation and independent assortment
were essentially mathematical models of how the “particles” of inheri-
tance—what we now call “genes”—were assorted and recombined in the
process of mating.
In other words, the “language” of genetics, like the “language” of physics
and chemistry, is essentially mathematical as well as logical. This emphasis
on mathematical rigor was almost certainly one of the reasons why the
early Mendelian geneticists and their supporters considered their theory of
the origin of species by means of mutations (rather than natural selection)
as a more rigorous and “scientific” theory of such origins.
As a consequence, the theory of evolution by means of genetic mutation
proposed by de Vries, Bateson, and their contemporaries was accepted by
most of the prominent geneticists at the turn of the century, and this led to
public testimonials that “Darwinism was dead.” But less than a decade after
the rediscovery of Mendel’s laws, two researchers, working separately and
mostly unbeknownst to each other, proposed a mathematical theory of evo-
lution that would eventually lead to the reestablishment of natural selection
as the prime mover of evolution.
During the first decade of the twentieth century, Godfrey H. Hardy, an
English mathematician, and Wilhelm Weinberg, a German physician, both
proposed a mathematical theory that describes in detail the conditions that
must be met for evolution to not occur. This theory, now often called the
Hardy-Weinberg equilibrium law, lays out the conditions that must be met
for there to be no changes in the allele frequencies in a population of inter-
breeding organisms over time. By systematically laying out these conditions,

60
the Hardy-Weinberg equilibrium law also makes it possible to show how
evolution does occur, by showing how and under what circumstances one
or more of these conditions can be violated, and what the consequences of
such violations would be.
In the context of evolution, alleles are what code for the characteristics of
organisms—that is, their phenotypes—that change over time in an evolving
population. Therefore, changes in the alleles present in a population will
produce changes over time in the phenotypes present in that population.
According to the Hardy-Weinberg equilibrium law,
Evolution is changes in allele frequency in populations over time.
Notice both the similarities and differences between this definition and the
one Darwin proposed in the Origin of Species. Darwin defined “descent
with modification” (what we call “evolution”) as changes in the characteris-
tics (that is, “traits”) in a population over time. Hardy, Weinberg, and the
other early geneticists changed one crucial term: they defined evolution as
changes in the allele frequencies in a population over time. This made sense,
given the definition of alleles, which was those “particles” of inheritance that
produced the traits of living organisms. This seemingly minor (and eminently
justifiable) substitution of “alleles” for “traits” made possible the mathemati-
cal analysis of the genetics of populations, a new branch of the natural sci-
ences now known as theoretical population genetics.
What Hardy and Weinberg realized is that for allele frequencies to not
change in a population, five conditions must be met:
1. There can be no mutations (that is, alleles cannot change into
other, different alleles).
2. There can be no gene flow (that is, individuals cannot enter or
leave the population).
3. The population must be very large (that is, random accidents can-
not alter allele frequencies).
4. Survival must be random (that is, there can be no natural selection).
5. Reproduction must also be random (that is, there can be no
sexual selection).
The Hardy-Weinberg equilibrium law outlines exactly what processes are
essential to prevent evolution, and therefore by negation it shows how evo-
lution can happen. If any of the five conditions for maintaining a Hardy-
Weinberg equilibrium are violated, then evolution must be occurring. And,
of course, virtually none of these conditions is ever permanently met in any
known natural population of organisms.
Therefore, according to the Hardy-Weinberg equilibrium law, evolution must
be occurring in virtually every population of living organisms. The law also
helps to show which of the factors listed is the most important in causing
evolutionary change in which groups of organisms.

61
 • Although they are always occurring, mutations do not occur often
enough to cause the kinds of changes that characterize most
observed evolutionary change. Mutations, in other words, provide
the raw material (that is, the “fuel”) for the engine of evolution but
are not the primary engine itself.
• Gene flow is often restricted in organisms that cannot move
around, such as fungi and plants. However, even among them,
genetic material gets moved from place to place. And, of course, in
animals gene flow is almost always a significant cause of deviations
from previous allele frequencies.
• As for population size, most actual breeding populations of organ-
isms are not large enough to ensure that there will be no changes
in allele frequencies as the result of purely random accidents (that
is, “sampling error”). Indeed, a previously unrecognized form of
evolution, called genetic drift, was proposed to occur whenever
populations are small enough for random accidents to cause
changes in allele frequencies.
• Survival is virtually never random, and nonrandom survival is just
another name for natural selection, Darwin’s proposed “engine” of
descent with modification. As a result of the formulation and wide-
spread acceptance of the Hardy-Weinberg equilibrium law and its
mathematical implications, natural selection eventually was once
again proclaimed the primary engine of evolution.
• However, there is another engine of evolution, at least among ani-
mals. Like survival, reproduction is also virtually never random
among animals, especially land animals who can choose who they
mate with. Therefore, sexual selection is also an important engine
of evolution in animals (and even in some plants).
The Hardy-Weinberg equilibrium law established the precedent that evo-
lution could be conceived of and mathematically modeled by reducing
whole organisms to single traits, coded for by combinations of single alle-
les. This radical reduction of complex concrete entities into simple abstract
mathematical relationships formed the foundation of the “modern evolu-
tionary synthesis.” The next lecture shows how three of the founders of the
new science of theoretical population genetics worked out most of the
mathematical equations that were used as the foundation of the “modern
synthesis” and how their theoretical work set the stage for the resurrection
of Darwin’s revolutionary theory.

62
 FOR GREATER UNDERSTANDING

Questions
1. Why was the Hardy-Weinberg Equilibrium Law so important to the
development of a mathematical theory of evolution?
2. What simplifying assumptions did Hardy and Weinberg have to make to
formulate their theory of genetic equilibrium?
3. What consequences, both intended and unintended, flow from these sim-
plifying assumptions?

Suggested Reading
Provine, William B. The Origins of Theoretical Population Genetics.
Chicago: University of Chicago Press, 2001 (1971).

Other Books of Interest

Larson, Edward J. Evolution: The Remarkable History of a Scientific Theory.
New York: Modern Library, 2006.
Mayr, Ernst. The Growth of Biological Thought: Diversity, Evolution, and
Inheritance. Cambridge, MA: Belknap Press of Harvard University
Press, 1985.
Ruse, Michael. Darwin and Design: Does Evolution Have a Purpose?
Cambridge, MA: Harvard University Press, 2004.

Websites of Interest
1. The University of Alberta (Canada) provides a PDF of G.H. Hardy’s
A Mathematician’s Apology (1940). —
www.math.ualberta.ca/~mss/misc/A%20Mathematician's%20Apology.pdf
2. The Secular Web features a paper from 2000 by Barbara Forrest entitled
“Methodological Naturalism and Philosophical Naturalism: Clarifying the
Connection.” —
http://www.infidels.org/library/modern/barbara_forrest/naturalism.html
3. The Stanford Encyclopedia of Philosophy features “Laws of Nature,”
written in 2003 and revised in 2010 by John W. Carroll and edited by
Edward N. Zalta. — http://plato.stanford.edu/entries/laws-of-nature

63
Lecture 10
Fisher, Haldane, and Wright
The Suggested Readings for this lecture are Ronald Aylmer Fisher’s
The Genetical Theory of Natural Selection and J.B.S. Haldane’s The
Causes of Evolution.

The Hardy-Weinberg equilibrium law provided a mathematical basis for the

founders of theoretical population genetics—principally R.A. Fisher, J.B.S.
Haldane, and Sewall Wright—to develop mathematical models for fitness,
selection, and other evolutionary processes. These models could then be
applied to demographic data derived from artificial and natural populations
of organisms in a rigorous and ongoing test of the validity of a neo-darwin-
ian model for genetic evolution.
They also provided the basis for what would eventually come to be known
as the “modern evolutionary synthesis,” in which Darwin’s theories of nat-
ural and sexual selection were combined with Mendelian genetics, biome-
try and statistics, demography, paleontology, comparative anatomy, botany,
and (more recently) molecular genetics and ethology to produce a “grand
unified theory” of the origin and evolution of life on Earth.
The work of English population geneticist and statistician Ronald Aylmer
Fisher further undermined the Mendelian theory of evolution via macromu-
tation by showing that the kind of continuous variation first proposed by
Darwin could provide the basis for natural selection.
In his most important work, The Genetical Theory of Natural Selection, pub-
lished in 1930, Fisher showed that traits characterized by continuous varia-
tion (that is, traits that approximate a normal, or bell-shaped, distribution)
were both common and could provide all the raw material necessary for
Darwinian natural selection. This is because such traits, although being con-
tinuous in populations, do not blend from parents to offspring because they
are produced by unblending “particles” of inheritance (that is, Mendelian
“genes”). In other words, Mendelian inheritance conserves, rather than even-
tually destroying, the genetic variation that exists in natural populations.
Fisher then proposed his fundamental theorem of natural selection:
The rate of increase in fitness of any organism at any time is equal to
its genetic variance in fitness at that time.
Essentially, Fisher’s theorem says that the degree of change that can result
from natural selection depends fundamentally on the amount of genetic
variation present in the population undergoing selection.
• If there is little variation, then natural selection cannot change the
characteristics of the members of the population much at all.

64
 • Conversely, if there is a lot of genetic variation, this can form
the basis for considerable evolutionary change as the result of nat-
ural selection.
This theorem, although modified somewhat today, forms the basis for most
of modern evolutionary theory. It also parallels an observation made by
Darwin in the Origin of Species: the more widespread and variable a
species is, the greater the effects of natural selection will be in that species.
Fisher’s theorem is a mathematical explanation of Darwin’s observation
about the variability of organisms in natural populations.
John Burdon Sanderson Haldane (usually referred to as J.B.S. Haldane) fur-
thered the revolution in theoretical population genetics begun by Hardy,
Weinberg, and Fisher. In his most important book, The Causes of Evolution
(1932), he showed that genetic mutations such as those observed by de Vries
and the early Mendelians could provide the raw material for Darwinian natur-
al selection. Furthermore, he showed mathematically that such mutations
could do this even when their frequency in a population was initially so low
that they would be “invisible” to statistical analysis. He also showed how
dominance could evolve in populations by means of natural selection, even
when the original expression of an allele was initially recessive.
Although Haldane did not propose any single theory in evolutionary biolo-
gy that could be called revolutionary, his approach, like Fisher’s, was. In
particular, Haldane stated the following:
The permeation of biology by mathematics is only beginning, but
unless the history of science is an inadequate guide, it will continue,
and the investigations here summarized represent the beginning of a
new branch of applied mathematics.
In The Causes of Evolution, Haldane developed a comprehensive mathe-
matical theory of genetic evolution based on Fisher’s pioneering work in
population genetics. Although much of the mathematics he presented was
based on Fisher’s original ideas, Haldane was able to apply them to very
practical problems, showing natural selection could produce many of the
outcomes originally proposed in nonmathematical form by Darwin. In par-
ticular, Haldane was able to show that natural selection could cause a trait
that was present in almost vanishingly low frequency in a population (so
small that it couldn’t be detected by normal statistical means) to become
overwhelmingly common in as few as 10,000 generations. While this may
seem like a long time, in geological terms it is almost a blink of an eye, and
in something like bacteria (which reproduce every twenty minutes or so), it
would be less than six months.
Haldane is also remembered for two quips that are often repeated by evo-
lutionary biologists. The first concerns a question posed to him by an
Anglican minister, who asked him (supposedly at a dinner party) what his
study of nature had led him to conclude about the principal concern of the

65
Creator. Without batting an eyelash, Haldane replied, “An inordinate fond-
ness for beetles,” referring to the fact that there are more species of beetles
on Earth than any other kind of organism).
During another conversation (supposedly in a pub), Haldane was confront-
ed with the observation that natural selection should result in pure selfish-
ness on the part of individuals, and therefore no one should be willing to
risk his own life to save another. To this Haldane replied, “I would be will-
ing to risk my life to save two brothers or eight cousins.” This quip is based
on the observation that brothers share an average of one-half of their genet-
ic material, whereas first cousins share an average of one-eighth. Therefore,
saving two brothers or eight cousins would result in the same genetic con-
tribution to the next generation as that represented by one’s own genome.
This quip was later cited by one of the founders of what is now known as
the theory of kin selection, in which natural selection is considered to act
at the level of genes, rather than individuals.
R.A. Fisher pointed out several times that the mathematics of natural selec-
tion were similar in many ways to such physical models as the ideal gas
laws and the second law of thermodynamics. According to his mathematical
models, alleles that were positively selected would increase in frequency in
populations in much the same way that gas molecules spread out in an
expanding balloon.
To many evolutionary biologists, this meant that natural selection would
inevitably result in “fixation” of alleles that were not selected against. That
is, any allele that resulted in increased survival and reproduction should, if
given enough time, inevitably become the only allele for that particular
trait. This presented a problem to evolutionary biologists by implying that
the inevitable result of natural selection would be the eventual elimination
of all nonadaptive variation in natural populations. This would then cause
natural selection to grind to a halt (or to become reduced to essentially the
rate of production of new genetic mutations, which is much slower than
the observed rate of evolution).
A solution to the problem was provided by Sewall Wright, who discovered a
process that has eventually become known as random genetic drift (or sim-
ply genetic drift). Wright proposed that in small populations of organisms,
random sampling errors could cause significant changes in allele frequencies
in such small populations. He showed mathematically that the smaller a pop-
ulation was, the greater the effect of such random events on its allele fre-
quencies. In other words, evolution could proceed by at least two primary
mechanisms: Darwinian natural selection and random genetic drift.
Wright then went on to develop a formal model for genetic evolution in
which the allele frequencies present in a population were visualized as
forming an adaptive landscape. In Wright’s model, the allele frequencies pre-
sent in a population were visualized as elevations in a topographical surface.

66
According to the prevailing theory at the time, selection could only cause
allele frequencies to ascend adaptive “peaks” in such a landscape, never
descend into the “valleys” of maladaptation. This meant that selection alone
could only result in fixation and eventual genetic stagnation, just as Fisher’s
equations for natural selection implied.
What Wright showed is that random drift could, in small populations,
cause allele frequencies to drift from one adaptive peak to another, and in
this way could keep evolution by natural selection moving. He called this
theory the “shifting balance theory of evolution,” as it emphasized the shift
from one adaptive peak to another by means of random genetic drift.
Wright carried out a long professional correspondence with Fisher, in
which the two agreed on the reality of genetic drift but disagreed on its
importance to evolution in general. Fisher was committed to natural selec-
tion as the principal “engine” of evolution. He argued that natural selection
would work fastest in large populations, in which there would be a reser-
voir of “hidden” genetic variation, in the form of recessive alleles in het-
erozygotes. This hidden variation could be brought out by changes in the
environment, when a recessive allele that was formerly deleterious could
become advantageous. Fisher pointed out that once the frequency of such
an advantageous recessive allele reached a level at which significant num-
bers of homozygous recessive individuals would be produced, the frequency
of the recessive allele would increase swiftly until reaching fixation. At that
point, with the formerly dominant allele then extinct, the formerly reces-
sive allele would become the new dominant allele and remain so until this
process repeated.
Wright, by contrast, believed that genetic drift played a very important part
in many populations. He argued that what might appear to be a large breed-
ing population was in many cases a mosaic of small breeding populations,
within which the actual “effective” breeding population was low enough
for random sampling error to produce the kind of genetic drift that he
believed could compensate for the tendency of natural selection to reduce
the amount of potentially adaptive variation in populations.
Wright also differed from Fisher and Haldane in his view of how individual
alleles affected the phenotypes of organisms. In the mathematical models
developed by Fisher and Haldane there was an essentially one-to-one rela-
tionship between individual genes and individual traits. Wright, by contrast,
believed that most phenotypic traits were the result of multiple genes inter-
acting with each other in complex ways. Wright pointed out that inbreed-
ing could expose such deleterious alleles relatively quickly, allowing them
to be weeded out of populations. He also became convinced that most evo-
lutionarily significant phenotypic traits were the result of multiple genes
interacting with each other, rather than the single genes rising and falling
in frequency that formed the basis of Fisher’s models of evolution.

67
 FOR GREATER UNDERSTANDING

Questions
1. What is R.A. Fisher’s fundamental theorem of natural selection, and what
does it imply about the ultimate outcome of natural selection?
2. What did J.B.S. Haldane demonstrate concerning the ability of natural
selection to change the frequency of rare alleles in populations and the
tendency for recessive alleles to eventually become dominant as the
result of natural selection?
3. Why was Sewall Wright’s theory of random genetic drift so important to
his theory of adaptive landscapes?

Suggested Reading
Fisher, Ronald Aylmer. The Genetical Theory of Natural Selection.
Charleston, SC: Nabu Press, 2010.
Haldane, J.B.S. The Causes of Evolution. Princeton: Princeton Science
Library, 1990.

Other Books of Interest

Larson, Edward J. Evolution: The Remarkable History of a Scientific Theory.
New York: Modern Library, 2006.
Mayr, Ernst. The Growth of Biological Thought: Diversity, Evolution, and
Inheritance. Cambridge, MA: Belknap Press of Harvard University
Press, 1985.
Ruse, Michael. Darwin and Design: Does Evolution Have a Purpose?
Cambridge, MA: Harvard University Press, 2004.

Websites of Interest
1. The Wikipedia entry on the “Price Equation” cites a number of authori-
tative sources for the information. —
http://en.wikipedia.org/wiki/Price_equation
2. The University of Southampton (UK) School of Social Sciences provides
A Guide to R.A. Fisher. —
http://www.economics.soton.ac.uk/staff/aldrich/fisherguide/rafframe.htm

68
Lecture 11
Natural Selection and Speciation
The Suggested Reading for this lecture is Ernst Mayr’s The Growth of
Biological Thought: Diversity, Evolution, and Inheritance, chapter 12,
“Diversity and Synthesis of Evolutionary Thought.”

R.A. Fisher, J.B.S. Haldane, and Sewall Wright are usually recognized as
having laid the theoretical foundation for modern evolutionary theory.
However, many evolutionary biologists and historians of science consider
that the “modern evolutionary synthesis” was initiated by Theodosius
Dobzhansky with the publication of his most famous book, Genetics and
the Origin of Species (1937). Dobzhansky combined Mendelian genetics,
the mathematical models of Fisher, Haldane, and Wright, and empirical
observations of evolution and natural selection in the wild in a theory that
reinstated natural selection as the primary engine of evolution.
Perhaps Dobzhansky’s most important contribution to the “modern synthe-
sis” was his confirmation of Fisher’s assertion that there is an immense
amount of “hidden” variation in most populations, in the form of recessive
alleles. By collecting fruit flies of several different species from different field
and laboratory populations, crossing them under controlled conditions in the
laboratory, and then analyzing the results of such crosses, Dobzhansky found
that even populations that appeared to be almost completely homogenous (at
the level of phenotypes) had a surprising amount of genetic heterogeneity at
the level of genotypes). This finding confirmed Fisher’s theoretical model
that such “hidden” variation could supply the “continuous variation” that
Darwin believed would be necessary for natural selection to proceed, but for
which Darwin had no mechanistic explanation.
This, in turn, added powerful empirical support to Fisher’s assertion that
natural selection alone could lead to the kind of large-scale evolutionary
changes visible in the fossil record. Rather than relying on the “saltational”
models of the early Mendelian geneticists, Fisher’s model could be called
“gradualist” and relied not on macromutations but rather on very small,
almost undetectable “micromutations,” spreading gradually through popula-
tions as recessive alleles in heterozygotes.
Dobzhansky’s field and laboratory studies also confirmed that Sewall
Wright’s newly discovered, but until then largely theoretical, process of ran-
dom genetic drift also happened in real populations. Again, by matching the
results of his crosses of small populations of fruit flies from relatively isolat-
ed populations, Dobzhansky was able to show that his results generally con-
formed to Wright’s predictions.
Among Dobzhansky’s other important contributions to the modern theo-
ry of evolution by natural selection was his analysis of the three different
69
patterns of evolutionary change that can result from natural selection:
directional selection, stabilizing selection, and disruptive selection.
To visualize each type, begin by considering the pattern of variation in a typi-
cal trait, such as beak length in Darwin’s finches. In such a population, there
is a natural (that is, random) variation in this trait, which is arrayed along the
X axis. The number of individuals showing a particular value of this trait is
entered along the Y axis. The result approximates a bell-shaped curve (that is,
a “normal distribution”) in which finches with intermediate-sized beaks—
what we could refer to as the “average” beak size—are the most common in
the population, while finches with very small or very large beaks are much
less common. Normal distributions of traits were central to R.A. Fisher’s
mathematical models of “continuous variation” of multigenic traits.
Consider the effect on the average value of this trait in the population if
individuals at one or the other (but not both) extreme of expression of this
trait are selected against (that is, have relatively lower survival and repro-
ductive success). The result would be a shift in the average value for the
trait in this population. For example, if finches with smaller beaks survive
less often or have fewer offspring, then finches with larger beaks would
have relatively higher reproductive success, and the average beak size for
the population as a whole would increase. Such a shift in the average value
for a particular trait in any population is a tip-off that selection is occurring
in that population. Since the overall effect of such selection is to cause a
unidirectional shift in the average value for a trait in a population, this kind
of selection is called directional selection. This is essentially the kind of nat-
ural selection that Darwin proposed in the Origin of Species.
An example of directional selection is the increase in mean beak size
among Galapagos finches as the result of prolonged drought, as studied by
Peter and Rosemary Grant. The Grants and their student assistants have
studied the population of the medium ground finch (Geospiza fortis) on the
island of Daphne Major in the Galapagos archipelago since 1973. They
observed the following in this intensively studied population of finches:
• Despite similar appearance, there is considerable variation among
these finches, especially with regard to the size of their beaks.
• There is also considerable variation in the relative survival and
reproductive rates of these finches, which can be correlated with
the changing ecology of the island.
• During periods of drought, there is a significant increase in the
average beak size in the population, corresponding to an increase in
the size and toughness of the seed food supply available to the
finches, and a corresponding decrease in the availability of smaller,
softer seeds.
• Developmental geneticists determined that the changes observed in
the relative sizes of the beaks of the finches can also be correlated

70
 with variations in the underlying genes that regulate the size of the
finches’ beaks.
In other words, there was a significant shift in the average size of the
finches’ beaks, correlated with an underlying genetic change, precisely the
kind of shift predicted by Dobzhansky’s model of directional selection, and
confirming Darwin’s original hypothesis for the evolution of adaptations by
means of natural selection.
Now consider a population in which selection is exerted most strongly
against individuals at both extremes of the range of variation in a particular
trait. The result of such selection would be no change in the average value
for the trait in the population, along with a noticeable decrease in the over-
all range of variation for the trait in the population. Since the effect of such
selection is to maintain the trait in question at or around the previously
existing population average, this kind of selection is called stabilizing selec-
tion (or “normalizing selection,” as Dobzhansky originally referred to it).
Stabilizing selection can have important implications for later evolutionary
change, as the decrease in overall variation in the trait in question can limit
the amount of change that can occur later if selection is relaxed. In
essence, once a population has been subjected to intense stabilizing selec-
tion, it is much less likely to shift later as the result of a change in the envi-
ronment, as there is less potential variation available for such a response.
Finally, consider a population in which selection is exerted most strongly
against individuals in the middle of the range of variation, which is usually
the largest fraction of the population. The effects of such selection would be
the production of a bimodal distribution of the trait under selection—two
bell-shaped curves, with a deep valley in between where the average value
for the trait used to be. The result of such selection would be a dramatic
increase in the amount of variation in the trait in the population, and the
splitting of the population into two distinct subpopulations, each with its
own characteristic average value for the trait in question. Because the origi-
nal average population value is eliminated and replaced by two different
averages, this kind of selection is called disruptive selection.
Disruptive selection is often called diversifying selection, as it results in
the production of increased diversity of traits in populations. As such, diver-
sifying selection has been implicated in evolutionary divergence and may be
a primary cause of speciation (that is, the origin of new species from exist-
ing ones). Dobzhansky proposed that this would be the case, asserting that
diversifying selection could explain the origin of new species from existing
species by means of natural selection alone.
And so, having considered Dobzhansky’s model for diversifying selection,
we come to what Darwin called the “mystery of mysteries”—the origin of
species. According to Darwin and all of his intellectual descendents, specia-
tion is the source of all of the diversity in life on Earth. It is also the biggest
mystery in evolutionary biology.
71
 As the title of his most famous book suggests, Darwin supposedly wrote
about the origin of species in the Origin of Species. However, he didn’t
really write much about speciation, except to suggest that it might be
caused by natural selection. Darwin’s main focus in the Origin (especially
the first half) was on the origin of adaptations by means of natural selec-
tion. Darwin believed that he had discovered a mechanism by which the
apparently purposeful characteristics of living organisms could have arisen
by purely natural processes that did not require any supernatural designer
or purpose.
Darwin did briefly address the problem of speciation (without calling it
that), but he concluded that the sterility that marks the boundaries
between closely related species could not have evolved by natural selec-
tion—after all, how can sterility increase by selecting for increasing
degrees of sterility? By definition, sterile organisms cannot pass on the
trait of sterility to their offspring.
The early Mendelians thought they had discovered a completely new
mechanism for speciation: macromutations, which not only produced new
species in as little as a single generation but also produced entirely new
functional adaptations. The problem with this idea was that it could not
easily be squared with the observation that almost all observable mutations
are too small and too deleterious to qualify as either the origin of new
species or as functional adaptations. Indeed, it is clear after reading some of
their proposals for speciation and adaptation via macromutation that they
believed in some kind of unspecified “magical” process by which just the
right macromutation would come along just when a species needed to
evolve into a new and different species.
Like Darwin, Fisher, Haldane, and Wright were most concerned with the
process of adaptation via natural selection and how that process could cause
significant changes in the average phenotypes in populations, rather than
how mutations and natural selection might cause one species to diverge
into two or more species whose members were incapable of interbreeding.
Dobzhansky had proposed a neo-Darwinian model for the origin of new
species, by means of diversifying selection. However, Dobzhansky’s model
did not square easily with Darwin’s skepticism about the inability of natural
selection to select for increasing degrees of sterility. Darwin himself had
suggested that some other process, which he could not specify or explain,
must somehow cause the decrease in interbreeding success that apparently
accompanies the divergence of two isolated subpopulations of one species
into two, non-interbreeding species.
The core concept that provided the “modern evolutionary synthesis” with
a testable theory of speciation was proposed by Ernst Mayr in his magnum
opus, Systematics and the Origin of Species, first published in 1942. In it,
Mayr attempted to answer two questions: What is a species? and How does
speciation occur?
72
 The most widely used definition of “species” is Mayr’s biological species
concept, which defines species essentially by reproductive isolation:
To be members of the same species, organisms must be capable of
interbreeding and producing fertile offspring under natural conditions.
Therefore, organisms that can’t do this (that is, organisms that are reproduc-
tively isolated from one another) are not members of the same species. This
concept was originally proposed by Dobzhansky in Genetics and the Origin
of Species, but Mayr developed it much more fully and integrated it into a
synthetic theory of the origin of species from previously existing species.
According to Mayr’s theory, speciation can occur whenever a small subset
of a larger interbreeding population becomes reproductively isolated from
the population of which it was formerly a part. Consider a simplified model
of such a large population. We can picture it as a large corral, with a defi-
nite boundary drawn around it like a fence. Inside this boundary all of the
members of the population are capable of interbreeding with each other
and producing fertile offspring. Such a population is referred to as panmic-
tic. Since a panmictic population is freely interbreeding (by definition), any
new allele (or other genetic element) that appears within this population
(that is, via mutation of an existing allele or by acquisition of a new allele
from another population via gene flow) can potentially spread throughout
the population.
If the new allele is a deleterious mutation (as most mutations apparently
are), it will be removed from the population, rapidly and completely if the
mutation is dominant, or slowly if the mutation is recessive. Once a delete-
rious mutation reaches a sufficiently low frequency in a population, it can
be completely removed as the result of random genetic drift.
However, if the new allele is either neutral (as often happens) or beneficial
(as rarely but occasionally happens), then it will tend to spread throughout
the population, so long as all individuals are freely interbreeding and it
doesn’t get eliminated accidentally by random genetic drift. If it is dominant
and beneficial (extremely unlikely, but possible), it will spread quite rapidly
through the population. In any case, the end result of this process will be
that any new allele will either disappear (as the result of selection or drift)
or spread through the population (if it is either neutral or beneficial). This
means that the whole population may change over time, but it will not
become separated into two or more subpopulations that are divergent and
(most importantly) genetically incompatible with each other.
However, if a small subpopulation of this original population becomes
reproductively isolated from it (that is, there is reduced or negligible gene
flow between the larger population and the smaller, isolated subpopulation),
then any new allele that occurs in either population will not spread to the
other. Therefore, the longer these two subpopulations are kept reproduc-
tively isolated from each other, the more different alleles (and other genetic

73
elements) will accumulate in each. Eventually, the accumulation of such
nonidentical genetic elements can result in partial or complete genetic
incompatibility between the two subpopulations, and they will then qualify
as two separate species, according to Mayr and Dobzhansky’s biological
species concept.
If we accept Mayr and Dobzhansky’s definition of a species, then the key
to speciation is anything that can cause reproductive isolation. This is easi-
est to understand when the cause is geographic isolation: that is, when
organisms are so far apart geographically that the probability of their mating
with each other is effectively zero. In technical terms, this is called “allopa-
try.” Speciation that results from allopatry is therefore allopatric speciation.
Central to Mayr’s concept of allopatric speciation is the idea that reproduc-
tive isolating mechanisms are incidental: they are not the result of natural
selection. In this, Mayr is following Darwin’s lead, who stated in the Origin
of Species that natural selection cannot possibly produce increasing degrees
of hybrid sterility or reproductive incompatibility. In later versions of his
theory, Mayr refined his idea of allopatric speciation, proposing that it is
most likely to happen when the small, isolated populations that separate
from their “parent” population are geographically located in small “islands”
at the periphery of the larger “continental” population. These two terms
are not used arbitrarily: some of the best examples of speciation are found
on small, isolated islands, such as the Galapagos archipelago, which are
located far from the mainland of South America. Because the small, isolated
populations are usually located at the periphery of their “parent” popula-
tion, Mayr called this process peripatric speciation.

74
 FOR GREATER UNDERSTANDING

Questions
1. Which kind of selection—directional, stabilizing, or diversifying—is most
like what Darwin originally proposed in the Origin of Species, and why?
2. Mayr’s “biological species concept” was extraordinarily useful in the
development of the theory of speciation during the formulation of the
“modern evolutionary synthesis.” However, it cannot be applied to a
wide range of living organisms and biological systems. Which ones and
why not, and can some other concept be used instead?
3. The title of Darwin’s most famous book—On the Origin of Species by
Means of Natural Selection—strongly implied that natural selection was
the principal mechanism driving the origin of new species from previous-
ly existing ones. Is this actually the case, and if not, what alternative
mechanisms did the “modern evolutionary synthesis” include?

Suggested Reading
Mayr, Ernst. The Growth of Biological Thought: Diversity, Evolution, and
Inheritance. Cambridge, MA: Belknap Press of Harvard University
Press, 1985.

Other Books of Interest

Dobzhansky, Theodosius. Genetics and the Origin of Species. New York.
Columbia University Press, 1982 (1937).
Larson, Edward J. Evolution: The Remarkable History of a Scientific Theory.
New York: Modern Library, 2006.
Mayr, Ernst. Systematics and the Origin of Species from the Viewpoint of a
Zoologist. Cambridge, MA: Harvard University Press, 1999 (1942).
Ruse, Michael. Darwin and Design: Does Evolution Have a Purpose?
Cambridge, MA: Harvard University Press, 2004.

Websites of Interest
The Ernst Mayr Library at Harvard University features archived material
and current resources in biology, including an extensive list of publications
by or about Ernst Mayr. — http://library.mcz.harvard.edu

75
Lecture 12
Disturbing Implications
The Suggested Reading for this lecture is Richard Dawkins’s The
Blind Watchmaker.

Most people are aware that the theory of evolution has some disturbing
implications. People who have thought about these implications often
assume that they have to do with their implications for religion. Yes, evolu-
tionary biology does indeed have implications that disturb some religious
believers. However, there are two very disturbing implications of evolution-
ary theory that trouble even some atheists:
1. Evolution by natural selection seems to rule out any possibility of
design, intention, or purpose in nature.
2. It also seems to rule out any possibility of human free will.
Consider the problem of purpose in nature. If you drop a rock, once it
leaves your grasp it falls to the ground. One can ask at least three funda-
mental questions about this process:
1. What does the rock do when you drop it?
Answer: It falls from your hand to the ground.
2. How does the rock fall to the ground?
Answer: It falls from your hand to the ground because of the force
of gravity.
3. Why does the rock fall to the ground?
Answer: The rock falls in order to reach the ground—or does it?
This is an explanation of the rock’s movement. However, it is not the explana-
tion that would be given by virtually any physicist today. This is because such
an answer would be based on a fundamental metaphysical assumption—that
someone or something (an “intentional agent”) intends the rock to fall to the
ground. Largely as the result of the work of Isaac Newton, physical scientists
do not include any reference to purpose when explaining natural phenomena.
In answering the “why” question posed earlier without resorting to inten-
tions or purposes, one is adopting a metaphysical worldview. This meta-
physical worldview, which forms the basis for virtually all of modern empir-
ical science, is formally known as methodological naturalism. According to
the principles of methodological naturalism, one simply investigates natural
processes using empirical methods and explains those processes without
speculating about why those processes happen the way they do. Answering
the question of how they do it is considered sufficient. To put it succinctly,
the answer to “how” questions in science is considered to be exactly the
same as the answer to “why” questions.

76
 By contrast, a “supernatural” explanation of the movement of falling
objects would begin with the assumption that there are “supernatural” enti-
ties or forces that govern such movement and can therefore answer the
question of why such processes happen. For example, one could answer
that the reason that dropped objects fall is that such objects are made of
“earth,” and as such are fundamentally “contaminated” or “tainted with
evil” and therefore attempt to reach the center of all evil (that is, the
underworld, or Hell), and are assisted in doing so by “agents of evil” (that
is, demons) that control their actions. While such an explanation would
strike most people today as absurd, it is surprisingly close to many prescien-
tific explanations of such actions.
A scientific explanation of the movement of falling objects would begin
with the assumption that there are “built-in” laws of nature that govern
such movement. According to most natural scientists, the universe is con-
structed in such a way that natural processes happen the way they happen
without any guidance or choice in the matter, and the formulation of such
laws has been built up over the past few centuries by the process of scien-
tific observation and experimentation.
The overwhelming majority of scientists have not retained any belief at all in
a supernatural agent that intervenes in nature, either in setting up the laws
that govern natural processes or in the working out of those processes on a
daily basis. In doing so, such scientists are adhering to a belief system known
as ontological naturalism, which is based on six metaphysical assumptions:
1. Nature (that is, the universe) contains only energy and matter, the
interactions between which cause all of the observable phenomena
in the universe.
2. The interactions between energy and matter (and only these inter-
actions) can involve the exchange of information.
3. Information separate from the interactions of energy or matter
can’t be shown to exist (and therefore is assumed not to exist).
4. The most useful way to understand the interactions between ener-
gy and matter is via empirical observation (and therefore the scien-
tific method is the best way to understand nature).
5. The simplest explanation of any natural phenomenon is assumed
to be the best, until proven otherwise (this principle is often called
“Occam’s razor” or the rule of parsimony).
6. It is not necessary to assume that intentions or purposes have any-
thing to do with natural phenomena and, since purpose in nature
is unnecessary to explain natural phenomena, it is assumed that
purpose does not exist in nature.
All of these are clearly metaphysical assumptions and are not directly veri-
fiable or falsifiable by any application of the scientific method as it is cur-
rently understood.
77
 Most people today wouldn’t say that dropped rocks fall “in order to” reach
the ground. But why does it not sound just as illogical to say that we have
hearts in order to pump blood through our arteries and veins? Does this
mean that our hearts and blood and arteries and veins are not natural
objects, and the pumping of blood by the heart is not a natural process? Are
biological organisms somehow different from other natural objects and
processes, and is that difference the inclusion of purpose in biology?
In 1970, Francisco Ayala, a student of Theodosius Dobzhansky and a win-
ner of the Templeton Prize, wrote a landmark paper on this subject, enti-
tled “Teleological Explanations in Evolutionary Biology.” In it, Ayala noted
that purpose as a part of evolutionary biology has been a “suspect” concept
since the formulation of the “modern evolutionary synthesis.” Evolutionary
biologists, especially during the “modern evolutionary synthesis,” tried to
remove all “purposeful” language from evolutionary explanations of biologi-
cal adaptations (the term “teleology” refers to the philosophical analysis of
the concept of purpose). However, it does not sound absurd to say that we
have hearts in order to pump blood through our arteries and veins. Ayala
argued that this is because evolutionary adaptations perform a specific func-
tion for organisms. This “function” can legitimately be considered to be
purposeful, although the process by which it has come to exist (that is, nat-
ural selection) is not.
In Ernst Mayr’s 1974 paper, “Teleological and Teleonomic: A New
Analysis,” Mayr agreed:
In spite of the long-standing misgivings of physical scientists, philoso-
phers, and logicians, many biologists have continued to insist not
only that such teleological statements are objective and free of meta-
physical content, but also that they express something important
which is lost when teleological language is eliminated from
such statements.
Mayr went on to refine Ayala’s concepts, using terminology that is com-
pletely consistent with other branches of the natural sciences. Specifically,
he proposed that all phenomena (that is, “natural” events) can be classified
as either teleological, teleomatic, or teleonomic.
• A teleological process or behavior is any goal-directed action.
Teleological processes are generally considered to be dynamic
rather than static; that is, they tend toward a particular end-state
(that is, a goal) by changing dynamically until the goal is reached.
• A teleomatic process is a teleological process that simply follows the
laws of nature, that is, leading to a result that is an automatic conse-
quence of physical forces, in which the reaching of its end state is
not controlled by a built-in program or an external intentional agent.
The law of gravity and the second law of thermodynamics are among
the laws of nature that govern teleomatic processes.

78
 • A teleonomic process or behavior is a teleological process that owes its
goal-directedness to the operation of a program. Like the term “teleo-
logical,” the term “teleonomic” implies active goal-direction. This, in
turn, implies a dynamic process rather than a static condition.
One way to distinguish a teleomatic process from a teleonomic one is that
teleomatic processes generally do not respond to deviations in such a way
as to return to their goal-directed path. If a dropped rock is deflected, it will
continue in the deflected trajectory rather than return to its original trajec-
tory. However, if a teleonomic entity is deflected or interfered with (such as
a bird being deflected from its flight toward a perch), it will compensate for
such deflection and, if possible, return to its original trajectory.
Central to Mayr’s distinction between teleomatic and teleonomic processes
is the existence of a guiding program in the case of teleonomic processes.
According to Mayr,
A program is coded or prearranged information that controls a
process (or behavior) leading it toward a given end. According to this
definition, a program is (1) something material, and (2) exists prior to
the initiation of the teleonomic process. Hence, it is consistent with a
causal (that is, purely natural) explanation.
Mayr distinguished between “closed” and “open” programs.
• A closed program is one in which the program itself generally can-
not be changed during the lifetime of the entity whose behavior it
controls. While this is easiest to apply to living organisms, in which
the “closed program” is the organism’s genome, it can also be
applied to such things as computer programs, especially if such pro-
grams cannot be modified as the result of interactions between the
entity and its environment.
• An open program is one in which the program can be modified dur-
ing the lifetime of the entity whose behavior it controls as the
result of interactions between the entity and its environment. In
living organisms, such modification can occur as the result of learn-
ing, although it could theoretically also occur as the result of devel-
opmental plasticity or horizontal gene transfer between organisms.
Also central to Mayr’s overall philosophical analysis is the distinction
between teleonomic processes (and the programs that control them) and
the mechanisms by which such processes evolve (that is, natural selection).
Teleonomic processes (that is, processes that are controlled by a program,
either closed or open) are fully “teleological,” in that they are directed
toward a goal that is defined within the parameters of the program.
Therefore, teleological (that is, “purposeful”) processes can exist and do not
violate naturalistic causality, so long as the program controlling them exists
prior to their execution and is encoded in some material form.

79
 This, in turn, entails the following implication: since the processes by
which the programs that control teleonomic processes arise (that is, natural
selection, and so forth) are not themselves purposeful, such programs are
relentlessly and inescapably driven by past experience, and past experience
alone. A teleonomic program cannot possibly plan for any future that has
not already participated in the modification of that program in the past.
This means that the future is quite literally “open” and in a very fundamen-
tal sense unknowable. There are no guarantees, at least none that can be
observed or inferred by the usual methods of natural science.
Therefore, it is neither illogical nor outside the bounds of ontological natu-
ralism (upon which modern science is based) to say that we have hearts in
order to pump blood through our arteries and veins. This is because we
inherit from our ancestors genetic programs that specify the assembly of
and regulate the operation of our bodies, including our circulatory systems.
These programs (encoded in our genomes) literally “preexist” us, and our
lives embody the working out of these programs, in combination with our
developmental environment.
However (and this is crucial), the programs themselves need not have come
into existence by a process that can in any way be considered as purposeful.
• If you do not make the jump from “need not” to “have not,” you
are a methodological naturalist.
• If you do make the jump from “need not” to “have not” (a jump
that is not entailed by any empirical observation or inference), then
you are an ontological naturalist.
Free Will
According to Professor William Provine of Cornell University, a noted his-
torian of science and recent winner of the David Hull Prize, evolutionary
biology has several philosophical and religious implications:
• The argument from design is dead, along with all gods worth having.
• Gods that work entirely through the laws of nature or that simply
create the universe and then let it run without further interference
are unharmed by the demise of the argument from design.
• Such gods are also utterly worthless.
Professor Provine has become notorious for asserting that “evolutionary
theory is the greatest engine of atheism ever devised.” According to this
viewpoint, if one accepts the underlying premises of the theory, several
implications immediately follow:
• There are no “ultimate” foundations for any theory of ethics. From
where in human evolution could such ultimate foundations possibly
have arisen?
• There is also no “ultimate” meaning in life, either individually
or collectively.
80
 • Human “free will,” as traditionally defined, does not exist.
Of these, the demise of free will is by far the most difficult to accept. Even
most atheists, including such prominent philosophers of evolutionary theo-
ry as Daniel Dennett, cannot accept the idea that human free will does not
exist. However, Professor Provine asserts that the concept of “free will” is
not only unintelligible, it is one of the very worst ideas ever invented, as it
justifies and provides additional fuel for the basic human desires for blame
and revenge.
Like Professor Provine, Charles Darwin believed in all of these implica-
tions of the theory of evolution. And, like Professor Provine, Darwin
believed that the loss of ultimate foundations for ethics, ultimate meaning
in life, and the idea of human free will carried little “sting.” Let’s consider
these implications one at a time:
• There Are No Gods Worth Having, Nor Any Life After Death:
Professor Provine has pointed out that the theory of evolution
implies that when you’re dead, “you’re dead, dead, dead!”
Professor Provine himself has a potentially fatal brain tumor and has
accepted his own mortality and that of those closest to him. He
believes that “the loss of gods is better for our rational minds and
our emotional health.”
• There Are No Ultimate Foundations for Ethics: Professor Provine
has also asserted that if any ultimate foundation for human ethics
did exist, its implications for ethics would be terrible. The environ-
ment that we live in changes so rapidly and in such fundamental
ways, that any “ultimate” (that is, unchanging and unchangeable)
theory of ethics would be an evolutionary “dead end” for any being
who was bound by it.
• There Is No Ultimate Meaning in Life: Professor Provine has point-
ed out that, although ultimate meaning in life may be nonexistent,
the proximate meanings that we find in life—our families, our
friends, the rewards of life in our communities, our work, and all of
the things that make day-to-day life liveable—are more than enough
to fill our lives with meaning. Indeed, believing fervently in some
“ultimate” meaning in life is often to ignore such sources of imme-
diate happiness and enjoyment, and to live a life set apart from (and
essentially denying the importance of) such proximate values.
• Human Free Will Is an Illusion: Finally, Professor Provine has assert-
ed that the concept of “free will” is logically unintelligible. It cannot
be defined in a way that avoids logical circularity or which does not
contradict what we understand about nature and evolution.
The concept of universal determinism (that is, that everything everywhere is
determined by some omniscient, omnipotent, omnipresent entity or force) is
both unprovable and irrelevant, especially to the concept of “free will.”
81
According to the theory of evolution, human actions and motivations are
entirely locally determined by a combination of heredity and environment and
the interactions between them. However, and contrary to the beliefs of some
scientists, one cannot reduce all human actions to chemistry and physics.
However, it is possible to reduce the cause of human actions to a combina-
tion of genetic information and environmental influences, without inferring
any other causes (such as supernatural influences or forces). Therefore,
according to Professor Provine, to assert that such supernatural influences
or forces exist is pointless and irrelevant.
Philosophers escape from the problem of the indefinability of the concept
of “free will” by erecting logically circular definitions of free will. They do
this primarily to preserve some justification for revenge. For example,
philosopher Ted Honderich defines “free will” in such a way as to preserve
our “retributive desires” (that is, our desire for revenge). This is just argu-
ing for something on the basis of its effects (which one desires), rather than
its logical coherence.
According to Professor Provine, we do not live on a planet on which organ-
ic beings have free will. He believes that this is good—he believes that the
recognition of the absence of free will can be the greatest boon for the
increase in kindness and understanding in society. He has emphasized that
he is not saying that we should not stop people from doing things of which
we do not approve. However, we can stop people from performing actions of
which we do not approve without resorting to revenge. By not making mon-
sters out of people who do “bad things” we make it possible to understand
them and their motivations and to work to end the cycle of revenge.
At some level, all human behaviors (both bad and good) have the same
“involuntary” quality—they are determined by our genetics and our person-
al histories. Hence, the concepts of both blame and praise are nonsensical,
except insofar as they alter our behavior in the future . . . and when they
do so, they are determining that behavior. Rather than expecting people to
use their free will to act morally, we must recognize that children (and
other members of society) can and must be programmed to act morally.
Acting morally is not innate in humans—anyone who has raised a two-year-
old knows this. The idea that human behavior can be “programmed” also
has implications for science and scientists. Scientists can be “programmed”
(that is, taught) to accept their hypotheses based on empirical evidence,
rather than on their beliefs or desires.
Finally, Professor Provine has pointed out that if you accept the foregoing,
it is also possible to see that atheistic science and religion can agree:
• Both counsel (for different reasons) that we should forgive sins.
• Both state that revenge is not a justifiable human response, regard-
less of our desire that it be so.

82
 FOR GREATER UNDERSTANDING

Questions
1. Computers can be programmed, just like living organisms are program-
med. Is there any fundamental difference between a computer and a liv-
ing organism?
2. Are religious beliefs necessary for people to behave morally?
3. Would we treat people differently if we believed that they had no
“free will”?

Suggested Readings
Dawkins, Richard. The Blind Watchmaker: Why the Evidence of Evolution
Reveals a Universe without Design. New York: Penguin, 2006.

Other Books of Interest

Dennett, Daniel C. Freedom Evolves. New York: Penguin, 2004.
Miller, Kenneth R. Finding Darwin’s God: A Scientist’s Search for Common
Ground Between God and Evolution. New York: Harper Perennial, 2007.
Ruse, Michael. Darwin and Design: Does Evolution Have a Purpose?
Cambridge, MA: Harvard University Press, 2004.

Websites of Interest
1. Cornell University provides a reprint of an article entitled “Teleological
and Teleonomic: A New Analysis” by Ernst Mayr that first appeared in
the Boston Studies in the Philosophy of Science, XIV, (1974) pp. 91–117.
— http://evolution.freehostia.com/wp-content/uploads/2007/07/
mayr_1974_teleological_and_teleonomic.rtf
2. The Faith + Evolution website provides links to five articles that debate
the concept of “free will.” —
http://www.faithandevolution.org/debates/is-darwinian-evolution-
compatible-with-free-will.php
3. The John Templeton Foundation’s The Humble Approach Initiative web-
site features the article “Purpose in Evolution: Is Convergence Sufficiently
Ubiquitous to Give a Directional Sign?” by Mary Ann Meyers, Ph.D.,
based on a foundation-sponsored symposium from 2004. —
http://humbleapproach.templeton.org/Purpose_in_Evolution

83
Lecture 13
Disastrous Digressions
The Suggested Reading for this lecture is Daniel J. Kevles’s In the Name
of Eugenics: Genetics and the Uses of Human Heredity.

Evolutionary biology is a natural science, like physics and chemistry. One of

the most fundamental principles of the natural sciences is that describing or
explaining something is not the same as advocating it. Physicists can
describe nuclear fission, and even point out how it could be used in a
weapon, without necessarily advocating that it be used for this purpose.
However, one of the common reactions many people have to the theory of
evolution and its implications for humans is that they assume that evolu-
tionary biologists are somehow advocating for evolution, or at least arguing
that it’s “natural” and therefore necessarily “good” or “right.” This is essen-
tially a confusion between the principles of “science” and the principles of
“morals” or “ethics.” As shown, science is the empirical study of nature—
what it is and how it works. By contrast, ethics is the philosophical study of
what we believe to be “good” and “bad,” “right” and “wrong,” and why
we believe such things.
The confusion between science and ethics is often framed as a confusion
between “is” and “ought”—the way the world is, as opposed to the way
we think it ought to be. Although it seems that people should see the fun-
damental difference between “is” statements and “ought” statements, many
people, including both opponents and supporters of evolutionary theory,
believe that “is” and “ought” not only can be reconciled, but may be the
very same thing.
Two episodes in the history of evolutionary thought illustrate this basic
confusion between “is” and “ought” statements: the rise and fall of social
Darwinism in the latter half of the nineteenth century and the rise and fall
of eugenics in the first half of the twentieth century. These two social
movements used evolutionary ideas and language to justify what were clear-
ly moral and political positions, rather than scientific principles, and as such
they constitute the two most disastrous digressions in the history of the sci-
ence of evolutionary biology.
Before addressing these two social movements, we should also clearly
draw a distinction between “science” and “technology.” We have already
considered what science is: the empirical study and explanation of what
nature is and how it works. Science is supposed to be dispassionate, objec-
tive, and unbiased.
But the same is not the case for technology, which is the application of
scientific knowledge for the “good” of humans and human society. The

84
inclusion of the word “good” in that definition indicates that technology,
unlike science, necessarily includes an ethical dimension. Strictly speak-
ing, science has no ethical dimension. There is nothing “good” or “bad”
about the molecular biology of the human immunodeficiency virus (HIV)
that causes AIDS. However, the development and use of antiviral drugs to
control HIV infections, while based on a thorough scientific understanding
of the molecular biology of HIV, is an application of that knowledge that is
intended to benefit people infected with the virus. The application of sci-
entific knowledge, unlike the acquisition of such knowledge, always
includes an ethical dimension.
Social Darwinism and eugenics weren’t sciences; they were technological
applications of evolutionary ideas. They involved the application of scientif-
ic ideas and information to what was intended by their advocates as the
betterment of humankind. Notice the word “intended.” As learned, scien-
tific descriptions of reality do not include intentions in explanations of how
nature works. This is particularly the case with evolutionary biology, which
began with Darwin’s theory of natural selection, which he developed specif-
ically because it did not require any design, intention, or purpose in nature
to bring about either adaptation or descent with modification. Both social
Darwinism and eugenics explicitly included both an ethical dimension and
intentions; they were intended to bring about a “better” society. What they
did instead was to lead to perhaps the most horrific perversion of both sci-
ence and morals in the history of Western civilization.
Social Darwinism and eugenics cannot be considered separately, nor can
they be completely separated from the science of evolutionary biology. The
social prescriptions worked out by the social Darwinists included concepts
taken directly from evolutionary biology and were in turn used by eugeni-
cists to further what they erroneously called the “science” of eugenics.
Both began in England in the latter half of the nineteenth century, but they
reached their highest pitch elsewhere: social Darwinism in America and
eugenics in America and Germany. And both collapsed and were finally
repudiated at about the same time: in the aftermath of World War II and
the social movements that arose out of it.
Social Darwinism is essentially an economic and political theory based on
the idea that natural selection tends to produce the “greatest good for the
greatest number” of the members of a society. If you are acquainted with
some of the language of ethical theory, you will recognize the phrase “great-
est good for the greatest number” as the foundational principle of utilitari-
anism, one of the two or three dominant forms of ethics in Western society.
According to its proponents, utilitarianism is justified by its effects: an
action is “good” or “right” if it tends to bring about the greatest good for
the greatest number of the members of a society; it is “bad” or “wrong” if
it does otherwise.

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 According to this viewpoint, social Darwinism is based upon the premise
that allowing natural selection to run its course is the most ethically justi-
fied position. Social Darwinists believed (there aren’t many of them now,
hence the past tense) that successful people deserve to be successful, while
unsuccessful people deserve to fail. Successful people represented the high-
est, most noble members of society, while unsuccessful people represented
the lowest, least deserving members of society.
Credit (or blame) for the invention and promotion of social Darwinism is
usually assigned to Herbert Spencer, an English economist, ethicist, philoso-
pher, and sociologist. Largely unremembered today, Spencer was unques-
tionably the most popular, influential, and widely read philosopher and
social theorist of the nineteenth century.
Spencer wrote one of the first book-length works on biology—Principles of
Biology, published in 1864—in which he coined the phrase “survival of the
fittest” to describe Darwin’s theory of evolution by natural selection.
Politically, Spencer was a radical nonconformist, opposed to the class sys-
tem in England and dedicated to the advancement of the middle and lower
classes. He believed that natural selection—“survival of the fittest,” in his
terminology—caused the most talented, hard-working, and therefore
deserving members of society to rise to positions of social prominence,
regardless of their social class. In particular, he forcefully argued that “lais-
sez-faire” economics—that is, economics with little or no governmental reg-
ulation—was the best system in which to promote the “survival of the
fittest” and therefore promote the best and brightest in society.
Spencer’s radical social theories met with considerable resistance in
England, where the social class system was firmly entrenched and which
many English believed to be hereditarily based. In America his ideas met
with considerably more success, not the least because his economic theo-
ries reinforced the nineteenth-century American political and economic sys-
tem of unfettered laissez-faire capitalism. Captains of industry like Andrew
Carnegie and Henry Ford promoted economic and social policies similar to
those advocated by Spencer, including the idea that those who had “risen
to the top” of society had a responsibility to help those less fortunate than
themselves . . . as long as those less fortunate were also hard-working and
didn’t demand special treatment (and, as we will see, were members of the
“right” race).
Historian Richard Hofstadter has argued that from the end of the Civil War
to the Great Depression, social Darwinism was the dominant social theory
in American economics and politics. It was opposed by the “progressives,”
many of them from the farm states of the Midwest, who believed that social
Darwinism was a regressive social system that held down the American
farmer and working man, who were the true foundation of America’s great-
ness. Perhaps their greatest champion was William Jennings Bryan, three
times Democratic candidate for president of the United States and secretary
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of state under Woodrow Wilson. Known as “the Great Commoner,” Bryan
fought the Republicans and their wealthy supporters, the big corporations
and the big banks, and advocated tirelessly for small farmers, small busi-
nessmen, and industrial workers.
Bryan is also famous for being on the “wrong” side in the “Scopes monkey
trial” in 1925. John T. Scopes, a high school biology and health teacher, was
arrested and put on trial in Dayton, Tennessee, for violating the Butler Act,
a law that made it “unlawful for any teacher in [Tennessee] . . . to teach
any theory that denies the Story of the Divine Creation of man as taught in
the Bible, and to teach instead that man has descended from a lower order
of animals.” Bryan volunteered to help the prosecution, while famous athe-
ist and defense attorney Clarence Darrow led Scopes’s defense. Unable to
call scientists as witnesses for the defense, Darrow called Bryan to the
stand and proceeded to humiliate him in the eyes of the public, through the
courtroom reporting of newspaper correspondent, H.L. Mencken.
Bryan is rightly accused of being a “creationist” at the Scopes trial, but he
was far from a “rube” or a proponent of ignorant and reactionary “funda-
mentalism.” On the contrary, Bryan was extremely well-read and educated,
and he took the political positions he did because of his commitment to his
progressive ideals. He believed that evolutionary theory (in the form of social
Darwinism) was a pernicious political doctrine intended to hold down the
farmer and working man, and hold up the captains of industry and the big
banks and “eastern trusts.” He used fundamentalist religion as a weapon in a
political battle against what he perceived to be the opponents of “the labor-
ing interests and the toilers everywhere.” It is one of the greatest ironies of
American history that “the Great Commoner” was a Democrat and opposed
the Republicans, who today by and large reject the theory of evolution and
progressive politics, while at the same time supporting big business and
laissez-faire capitalism.
Social Darwinism fell rapidly from prominence in American social theory
during the Great Depression and the “New Deal” era. The Republican
Party, which had presided over the boom years of the 1920s, was blamed
with bringing on the Great Depression and was driven from political power
for a generation. Following the Great Depression and taking hold during the
administration of Richard Nixon, both the Democratic and Republican par-
ties underwent a paradoxical transformation. The Democratic Party, which
had been the party of rural America, the “solid (and racist) South,” and reli-
gious fundamentalism and anti-evolutionism, became the party of urban
America, the east- and west-coast educated “elites” and pro-evolutionism,
while the Republican Party became the party of the rural South, the
Midwest, the intermontane West, and anti-evolutionism.
According to the organizers of the Second International Eugenics
Conference, eugenics is “the self-direction of human evolution.” The roots

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of eugenics go back to the ancient Greeks. Plato, in his Republic, advocated
for a system of eugenic mating, in which people with desirable characteris-
tics (such as philosophers) would be given preference in mating over those
with less desirable characteristics. The Spartans of ancient Greece had a tra-
dition of “exposing” deformed, unwanted, or weak infants to the elements
(thereby killing them) as a way of improving the strength and toughness of
the survivors. In Roman society, Roman law required that “deformed”
infants be destroyed and that patriarchs could “dispose” of unwanted chil-
dren by giving them away, selling them into slavery, or killing them.
Eugenics as a so-called science began with Francis Galton, a polymath and
the cousin of Charles Darwin. He coined the term “eugenics” in 1883,
defining it as “the study of all agencies under human control which can
improve or impair the racial quality of future generations.”
Galton was deeply influenced by his cousin’s Origin of Species. He was
particularly influenced by the first chapter, in which Darwin discussed
selective breeding in domesticated animals and plants. Galton became con-
vinced that humans had been bred, unconsciously but nonetheless system-
atically, as the result of economic and social policies that governed who
could marry and have children.
According to Galton, the social classes of England were primarily the result
of hereditary traits, especially intelligence, with the lower classes being less
intelligent and the upper classes more intelligent. He developed a number
of statistical methods for analyzing intelligence, some of which became the
precursors of modern intelligence (“IQ”) tests. He believed that the various
human races, genders, and social classes were genetically distinct, with
white, Anglo-Saxon males at the pinnacle of the species and black African
females at the bottom. Asians, he believed, were somewhere in the middle,
and he advocated their emigration to Africa, where they could rebuild their
ancient civilizations and reclaim the riches of the African continent from
the black Africans, who had no use for such riches and were despoiling
their environment and wasting its resources.
Galton mostly advocated what has been called “positive eugenics,” a social
system in which those people judged to be “superior” would be encouraged
(through financial, political, and social incentives) to have more children.
He based this policy on his observation that the less desirable members of
English society—the lower classes, and especially Catholics—were repro-
ducing at a much higher rate than the more desirable members of society—
the upper classes, especially Protestants. His most famous book on this sub-
ject—Hereditary Genius, published in 1869—presented his criteria and
methods for measuring and comparing human intelligence, and laid the
groundwork for his proposals for encouraging the “intellectual elite” to
increase their reproductive rate.
Like social Darwinism, Galton’s ideas of “positive eugenics” were less
influential in England than in America. Perhaps some of this difference can
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be explained by the legacy of slavery in the United States. The English abol-
ished slavery earlier than the United States and did not seem as inclined as
Americans to justify it on the basis of racial inferiority. That this is the case
is illustrated by the fact that the first “eugenic” laws to be enacted were
laws prohibiting miscegenation—that is, marriage between people of differ-
ent races—mostly, but not exclusively, in the states of the former
Confederacy. The South was not alone in this, however. Many states,
including northern and eastern states, passed laws during this same period
regulating who could marry and under what conditions. The now wide-
spread idea that the government could regulate marriage through the
issuance of marriage licenses has its roots in the eugenics movement of the
late nineteenth and early twentieth centuries. Such regulations were
intended to limit the reproduction of genetically unfit people, by prohibit-
ing marriages between close relatives and between people with “social dis-
eases” and “genetic defects.”
The eugenics movement in America had many supporters, including some
who are still remembered and revered in American history for other rea-
sons. For example, L. Frank Baum, author of The Wizard of Oz and other
children’s books, was a racist and eugenicist who advocated the extermina-
tion of the plains Indians. Supreme Court justice Oliver Wendell Holmes Jr.
wrote the majority opinion in the 1927 case of Buck v. Bell, in which the
court upheld the state-enforced sterilization of a Virginia woman who was
claimed to be of below-average intelligence:
It is better for all the world, if instead of waiting to execute degener-
ate offspring for crime, or to let them starve for their imbecility, soci-
ety can prevent those who are manifestly unfit from continuing their
kind . . . Three generations of imbeciles are enough.
John Harvey Kellogg, founder of the Kellogg’s cereal company of Battle
Creek, Michigan, was also a dedicated eugenicist, founding the Race
Betterment Foundation with Irving Fisher and Charles Davenport in 1906
(more on Davenport in a minute). Kellogg was strongly in favor of racial
segregation and believed that immigrants and especially non-whites would
damage the American gene pool. Finally, Margaret Sanger, founder of
Planned Parenthood and icon of the feminist movement, was a dedicated
eugenicist who believed that the “positive eugenics” of the English was
mostly ineffective.
Whereas most English eugenicists advocated “positive eugenics,” some of
the most influential American eugenicists advocated “negative eugenics”—
that is, the prevention of marriage and interbreeding of people deemed
genetically inferior, up to and including forced sterilization of people
deemed sufficiently degenerate as to present a “drain” on society.
Chief among the American advocates of negative eugenics was Charles
Benedict Davenport. An early convert to Mendel’s theory of genetics,

89
Davenport was made director of the Cold Spring Harbor laboratory of
experimental genetics on Long Island in 1898. While there, in 1910, he
founded the Eugenics Record Office, which became a center for the study
of human genetics and heredity, and one of the organizing centers of the
American eugenics movement.
That movement was extraordinarily successful during the first four decades
of the twentieth century. Eugenics was a regular topic of popular books and
articles in the public press. Speakers promoted eugenics in public meetings
and private organizations, and local eugenics societies sprang up around the
country. Undergraduate and graduate courses in eugenics were offered at
many American colleges and universities. By 1928, there were 376 college
and university courses in eugenics in the United States.
The American eugenics movement, spearheaded by Davenport, had per-
haps its greatest impact on the eugenics movement in Germany. In 1916,
Madison Grant, an American lawyer, eugenicist, and historian, wrote The
Passing of the Great Race, or the Racial Basis of European History, in
which he asserted that the Nordic race was the most advanced among
human racial groups, and that immigration, “race-crossing,” and social poli-
cies that allowed blacks, Jews, and other “inferior” races to replace Nordics
at the pinnacles of society were destroying the “great Nordic race.” Grant
advocated anti-miscegenation laws, such as Virginia’s Racial Integrity Act of
1924, where the “one drop rule” (which classified anyone with any African
ancestors at all, no matter how few or how distant, as “Negro”) was made
the basis for discriminatory laws.
Grant’s book never became a best-seller in the United States, but in
Germany the situation was very different. Under Adolf Hitler, the Nazi party
made “racial purity” part of the foundation of the National Socialist political
platform. The Passing of the Great Race was reinterpreted by Alfred
Rosenberg, the principal Nazi race propagandist, as referring to the Aryan
race, whose greatest enemy and perennial opponent was the culturally and
genetically degenerate Jewish race. After the Nazi takeover of power in
Germany in 1933, the so-called “Nuremburg Laws” were promulgated, out-
lawing intermarriage between Jews and other Germans and stripping Jews of
their German citizenship. The Nuremburg Laws also made extramarital sex
between Jews and non-Jews illegal, and even went so far as to prohibit Jews
from hiring German women as housekeepers for Jewish households.
Beginning in 1934, a series of laws requiring forced sterilization were put
into effect in Germany. These laws were modeled after similar laws passed
in several American states, especially California and Virginia. In the United
States more than 64,000 people (predominantly women) were sterilized
against their will between 1907 and 1963. In Germany under similar legis-
lation, more than 400,000 people were forcibly sterilized between 1933
and 1945 under the Law for the Prevention of Hereditarily Diseased

90
Offspring. Put in force in July 1933, this law required physicians to report
to the government every case of hereditary illness they encountered (except
in post-menopausal women), or pay a fine.
Forced sterilizations were only the beginning. In May 1939, the Committee
for the Scientific Treatment of Severe, Genetically Determined Illness was
established at the express order of Adolf Hitler. Its function was to develop
criteria for use in a systematic program of infanticide, designed to kill infants
identified as having genetic or developmental disabilities. Jewish infants
were automatically included, as simply being Jewish was defined as a degen-
erative genetic disease. In September, simultaneous with the outbreak of the
war, this program was expanded into what was known as the T-4 program
(an abbreviation for “Tiergartenstraße 4,” the address in Berlin where the
headquarters of the program was located. The name of this program was
“The Charitable Foundation for Cure and Institutional Care.” Its mission, as
stated in Hitler’s explicit order, was so “that patients considered incurable
according to the best available human judgment of their state of health, can
be granted a merciful death.” Between 1939 and 1945, at least 200,000
physically or mentally handicapped people were killed by medication, starva-
tion, or gas chamber.
But forced euthanasia was only the beginning. On January 20, 1942, mem-
bers of the upper echelon of the Nazi government met to inform the various
government officials responsible for government policies and regulations per-
taining to Jews that Reinhard Heydrich had been named as the chief execu-
tor of the “final solution to the Jewish question.” Heydrich presented a plan
for the forcible deportation of the Jewish population of Europe and north
Africa to German-occupied areas in eastern Europe. There they would be
sorted, and those among them who were able-bodied would be assigned to
hard labor on road-building projects, in the course of which they would
eventually die from overwork, disease, or starvation. Any surviving Jews
(and those deemed unfit for such labor) would be exterminated.
That was the plan; however, as the war progressed and German troops
were pushed back toward the pre-war borders of Germany, the plans to use
the deported Jews (and others, including gypsies, homosexuals, and the able-
bodied mentally ill) for road-building and other labor projects were aban-
doned, and the captive populations were simply killed. The extermination
programs were accelerated as the Allies pushed closer to Germany, with the
intention that all evidence of the camps be destroyed before they were dis-
covered by the Allies. However, as German military strength collapsed fol-
lowing the failed invasion of Russia, the Allies moved more quickly than the
Nazi bureaucracy could react, so many of the camps were liberated before all
of their inmates could be killed and their bodies cremated.
The horrors of World War II and the Nazi holocaust put an end to the
eugenics movement. Its association with the atrocities committed by the

91
Nazis made it so unpopular that virtually all colleges and universities
stopped teaching courses in eugenics, publishers stopped printing (and the
public stopped reading) books on the subject, and anyone who wrote or
spoke about eugenics with anything except horror and revulsion was
lumped together with the Nazis. At the Nuremburg trials in 1945–46, at
which the Nazi leadership was tried for war crimes and “crimes against
humanity,” the “negative eugenics” programs were included among such
crimes. The surviving Nazi leaders who promoted such programs were exe-
cuted, and those who supported them were imprisoned. In 1950, the
United Nations Economic, Social, and Cultural Organization (UNESCO)
issued a statement on race in which the concepts that formed the basis of
eugenics were explicitly repudiated. This statement was revised three
times, in 1951, 1967, and 1978, with input from geneticists and evolution-
ary biologists, including Theodosius Dobzhansky.
Was the eugenics movement a product of the science of evolutionary biolo-
gy? Although eugenicists used much of the vocabulary of evolutionary biolo-
gy and genetics, the answer to this question is clearly no. Like the relation-
ship between nuclear physics and nuclear weapons, the relationship
between evolutionary biology and eugenics was essentially the relationship
between a science and a technology that used some of the principles of that
science for political and social purposes.
However, if one asks a slightly different question—do scientists, including
evolutionary biologists, bear any responsibility for the horrors of war and the
Holocaust?—the answer is yes if they did not speak out against such things
once their evil aspects had become known. Anyone who does not resist evil,
scientist and nonscientist, evolutionary biologist and creationist, male and
female, of any and all races, religions, ethnic backgrounds, and sexual orien-
tations, who perceives that evil is being done and does nothing to stop it is
responsible for that evil. As Edmund Burke once wrote, “All that is neces-
sary for the triumph of evil is that good men do nothing.”

92
 FOR GREATER UNDERSTANDING

Questions
1. What is the relationship, if any, between ethics, morals, and science?
2. Does unrestricted laissez-faire competition necessarily promote the
“greatest good of the greatest number” in human society?
3. Is eugenics currently “dead,” or has something very similar (but with a
different name) taken its place?

Suggested Readings
Kevles, Daniel J. In the Name of Eugenics: Genetics and the Uses of
Human Heredity. Cambridge, MA: Harvard University Press, 1998.

Other Books of Interest

Black, Edwin. War Against the Weak: Eugenics and America’s Campaign to
Create a Master Race. New York: Dialog Press, 2008.
Gould, Stephen J. The Mismeasure of Man. New York: W.W. Norton &
Co., 1996.
Hofstadter, Richard. Social Darwinism in American Thought. Boston:
Beacon Press, 1992 (1944).

Websites of Interest
1. This site from Allen MacNeill features a PDF of Brian Kaviar’s 2003
Tallman Prize-winning essay “A History of the Eugenics Movement
at Cornell.” —
http://macneill.allen.googlepages.com/2003_Tallman_Prize_Kaviar.pdf
2. Fordham University’s Modern History Sourcebook website provides an
article by Paul Halsall entitled “Herbert Spencer: Social Darwinism,
1857” from a paper by Spencer entitled “Progress: Its Law and Cause,”
which specifically discusses race and class. —
http://www.fordham.edu/halsall/mod/spencer-darwin.html

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Lecture 14
A Temporar y Unity
The Suggested Reading for this lecture is George Gaylord Simpson’s
Tempo and Mode in Evolution.

Jacob Bronowski, author of The Ascent of Man, famously described the

theories of quantum mechanics and relativity in physics as the “greatest
collective work of art of the twentieth century.” Essentially the same could
be said of the “modern evolutionary synthesis.” It involved the collective
work of hundreds of field ecologists, laboratory biologists, mathematicians,
and theoreticians from around the world. Historian William Provine has
stated that the “modern evolutionary synthesis” was essentially complete
by 1959, when it was celebrated at the centennial of the publication of the
Origin of Species at Chicago University. At that celebration, many of the
participants in the “modern synthesis” got together to compare notes, to
reminisce about their work together, and to present papers that consolidat-
ed the broad outlines of the synthesis for posterity.
The “modern evolutionary synthesis,” like Darwin’s Origin of Species, was
a true synthesis, spanning nearly all of the major disciplines of the biologi-
cal sciences and including scientists from many different nations. So far, all
of the contributors to the “modern evolutionary synthesis” have been
geneticists or population geneticists. However, scientists from other disci-
plines also contributed to the synthetic theory.
Principal among these was George Gaylord Simpson, curator of the depart-
ments of geology and paleontology at the American Museum of Natural
History in New York, and later curator of the Museum of Comparative
Zoology at Harvard University in Cambridge, Massachusetts. Simpson was a
paleontologist, that is, a scientist who studies ancient (and usually extinct)
organisms, usually by studying their fossils and other remains. He was an
expert in comparative anatomy, particularly of mammals, and most especially
of horses and their evolutionary ancestors. In his most important book,
Tempo and Mode in Evolution (first published in 1944), Simpson presented
two major concepts that were essential to the modern evolutionary synthesis:
• That the fossil record generally supports the theories presented
by population geneticists, especially Fisher, Haldane, Wright,
and Dobzhansky.
• That the pace at which evolution has occurred has varied over geo-
logic time, based primarily on observations of the fossil record.
The first idea was probably less important in the long run than the second.
The reason was that Simpson’s suggestion that the rate of evolutionary
change could speed up or slow down seemed to some evolutionary biologists
to depart somewhat from Darwin’s theory, which most evolutionary biologists

94
interpreted as implying that evolution was both continuous and gradual. As
we will see, this idea was challenged in 1972 by Niles Eldredge and Stephen
J. Gould in their landmark paper on punctuated equilibrium. This develop-
ment was particularly ironic, as Simpson is usually credited with bringing
paleontology into the “modern evolutionary synthesis,” whereas Eldredge and
Gould are perhaps the most famous challengers to that same synthesis.
Another central figure in the “modern evolutionary synthesis” was
German ornithologist Bernhard Rensch. His name is often left out of
accounts of the development of the “modern synthesis,” mostly because his
books and scientific publications were almost all published in German. The
one major exception was his 1947 book, Evolution Above the Species Level.
In it, Rensch presented a theory of speciation very similar to the theory pro-
posed by Ernst Mayr, along with much supporting evidence from his own
work. More importantly, Rensch argued forcefully that the same mecha-
nisms that cause the origin of new species from existing ones could also
explain the origin of all of the higher taxa (genera, families, orders, classes,
phyla, and even kingdoms). Rensch’s argument was essentially that all of
the higher taxa originated by the same mechanisms as species—principally
natural selection, but also (possibly) genetic drift—and that the main differ-
ence between the origin of new species and higher taxa was the much
longer spans of time involved in the latter. According to Rensch, there is
fundamentally no difference between microevolution—natural selection and
genetic drift acting over relatively short periods of time within popula-
tions—and macroevolution—those same mechanisms extended over mil-
lions or billions of years.
Finally, in 1950, botanist G. Ledyard Stebbins published Variation and
Evolution in Plants, which extended the “modern synthesis” to plants.
Stebbins showed how natural selection and genetic drift could be used to
explain virtually all of the evolution of plants, and he thereby put an end
to the remnants of Lamarckian thinking, which still persisted among some
botanists at that time. Stebbins’s contribution to the “modern evolutionary
synthesis” was twofold: it extended the theoretical population genetic
models of Fisher, Haldane, and Wright to plants (something that only
Haldane originally attempted), and it put the final nail in the coffin of non-
Darwinian evolutionary mechanisms, such as Lamarckian inheritance of
acquired characteristics.
By 1959, most biologists (following Ernst Mayr’s lead) agreed that evolu-
tionary theory had been “unified” and that it had reached its final form.
Among the tenets of the “unified” theory of evolutionary biology at that
time were the following:
• That evolution is best defined as “changes in allele frequencies in
populations over time.”
• That there is an essentially direct one-to-one correspondence
between genes and the traits for which they code.
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 • That the genomes and resulting phenotypes of most organisms are
essentially “homeostatic” over time—they react to perturbations by
returning to a balance of adaptive characters or change smoothly
over time via directional selection.
• That genetic recombination is more important than mutation as a
source of variation.
• That natural selection is the primary mechanism of evolution at
all levels.
• That competition, especially between members of the same species,
is the principal driving force in natural selection.
• That genetic drift is also an important mechanism in evolution,
explaining changes (such as the “founder effect”) that happen in
small populations.
• That the inheritance of acquired characters (that is, Lamarckian
inheritance) is either impossible or irrelevant to biological evolution.
• That the evolution of gross phenotypic characteristics (such as
eyes, wings, and so forth) is a good model of evolution at the mole-
cular level.
• That the “biological species concept” provides an unambiguous and
widely applicable definition of nearly all species.
• That speciation is almost completely understood, at least in principle.
• That speciation is virtually always the result of geographic isola-
tion (allopatry).
• That macroevolution (the origin and evolution of higher taxa) pro-
ceeds via essentially the same mechanisms as microevolution (that
is, natural selection, sexual selection, and genetic drift).
• That neither design nor purpose played any part in biological evolu-
tion, nor in biology in general.
This grand unified theory of evolutionary biology was an extraordinary
achievement, as significant as the collective formulation and elaboration of
the theories of quantum mechanics and relativity in physics, although less
well known. The celebrants at the Chicago centennial could be justly proud
of having produced a synthetic theory at least as fully realized as Darwin’s,
and supported by much more field and laboratory research.
However, it should also be said that the collective achievement of the mak-
ers of the “modern synthesis” simply amplify Darwin’s extraordinary
achievement. His theory, like theirs, was a truly synthetic theory, drawing
together animal and plant breeding, theoretical population ecology, natural
history, animal behavior, paleontology, biogeography, embryology, and sys-
tematics. And both theories—in 1859 and 1959—were truly revolutionary.
They both upended the theories of the origin of species and adaptation that

96
preceded them, and both generated controversies among the general public
and among scientists.
There is one significant difference between Darwin’s synthesis and its
“modern” counterpart: Darwin did not believe that his theory was the final
comprehensive answer to the questions of the origin of species and adapta-
tions. In the Origin of Species, Darwin was very candid at pointing out the
weak points in his theory, and especially those parts of the theory for which
there was little or no evidence, and even those parts which were almost
entirely speculative. The same cannot be said for the “modern evolutionary
synthesis.” It was almost immediately incorporated into biology textbooks,
where it remains almost unchanged to this day. When creationists challenge
the theory of evolution, the version of the theory that they challenge is
almost always the version at the heart of the “modern synthesis” as it was
conceived of in 1959. And when evolutionary biologists come to the
defense of evolutionary theory, the theory they usually defend is the one
still known as the “modern evolutionary synthesis.” That theory, in other
words, has done something that evolutionary biologists have asserted can’t
happen: it has not evolved.
This amounts to evolutionary biology’s “best kept secret.” Considered
from the perspective of the half century that has passed since 1959, most
historians of evolutionary biology now know that almost all of the major
tenets of the “modern synthesis” listed earlier were either grossly inaccu-
rate or just plain wrong. Research and additional theoretical work since
1959 has shown the following:
• That “changes in allele frequencies in populations over time” is a wholly
inadequate definition for much of the evolution revealed by the fossil
and genomic records.
• That genes and traits are only weakly associated (that is, the “one
gene–one enzyme” theory does not apply to most of the genome,
and when it does it does so in peculiar and unpredictable ways).
• That the genomes of most organisms are chaotic, with bits and pieces of
gene sequences being added, removed, and rearranged in nearly random
patterns, often by “parasitic DNA.”
• That there are at least fifty different mechanisms that produce genetic
and phenotypic variation, of which recombination is only one (and per-
haps not the most important one).
• That mutation is immensely important, not only as a source of evolution-
ary novelty but also as a source of overall genetic change, especially in
short-lived organisms such as bacteria.
• That much of evolution is selectively neutral, especially at the level of
nucleotide sequences in DNA.
• That natural selection is only one mechanism of microevolutionary
change, and possibly not the most important one.
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 • That cooperation, especially between members of different species, has
been a crucial process in evolution, especially macroevolution.
• That much of the genome of most organisms, especially eukaryotes such
as ourselves, is stuffed with redundant sequences, modular gene seg-
ments, and regulatory regions that do not code for polypeptides at all,
but some of which are nevertheless essential to phenotypic expression.
• That random genetic drift is not an important mechanism in evolution
(and may not even exist, at least in the way described by Sewall Wright).
• That the inheritance of acquired characteristics is a real and potentially
very important mechanism of biological evolution (important enough to
be given its own name, “epigenetics,” a rapidly developing subdiscipline
of evolutionary genetics).
• That phenotypic and protein evolution is largely decoupled from
the evolution of much of the DNA sequence in most organisms, espe-
cially eukaryotes.
• That the biological species concept is largely inadequate to characterize
species at many levels (especially the most abundant and diverse organ-
isms on Earth, the bacteria), and that uncritical adherence to it has
inhibited research into the mechanisms of speciation.
• That the mechanisms of speciation, like those of macroevolution, are still
largely unknown.
• That speciation not only can happen without geographic isolation (a
process called sympatric speciation), but may happen that way much of
the time.
• That macroevolution proceeds by fundamentally different mechanisms
than microevolution, and that these macroevolutionary mechanisms are
still largely unknown.
• That microevolution and macroevolution can both be saltatory—indeed,
macroevolution almost always is.
• That the use of teleological language—that is, “design” and “purpose”—
is legitimate when describing the development of organisms via the
expression of their genetic programs, but that neither design nor pur-
pose play any part in the evolution of those programs.
As recent investigations of the whole genomes of several species have
shown, the vast majority of the underlying genetic code of living organisms
does nothing like what the originators of the “modern synthesis” thought
the genome was doing. It is essentially a “boiling chaos” of noncoding
genetic information, which mutates at an astonishingly high rate, with
effects that we have only begun to understand.
This does not undermine the importance of natural selection in evolution,
at least not insofar as it is believed to be the basis for adaptations. However,

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following John Endler’s lead (in his landmark book, Natural Selection in the
Wild, published in 1986), some evolutionary biologists now no longer con-
sider natural selection itself to be a “cause” of anything. It is, rather, an
effect—that is, an outcome caused by other processes:
1. Variation, both genetic and phenotypic, resulting from mutation,
genetic recombination, and epigenetic transformation.
2. Inheritance, both genetic and epigenetic, resulting from the
expression of the genetic code and its interactions with the envi-
ronment of its carrier.
3. Population expansion and contraction, resulting from the general
tendency of organisms to produce more offspring than is necessary
to replace themselves, but also from such catastrophic processes as
mass extinction and adaptive radiation.
4. Differential survival and reproduction, including both direc-
tional change and purely random changes in both genotypes
and phenotypes.
These four underlying conditions, working together, produce the changes
in genotype and phenotype that we call “natural selection.”
Overall, the evolution of the theory of evolution has swung back and forth
like a huge pendulum, in approximately fifty-year cycles:
• 1759 to 1809: formulation of the species concept and the system of bio-
logical classification, based on the Systema Naturae of Linnaeus, which
assumed the origin of species by means of special creation by God.
• 1809 to 1859: Lamarckian evolution by inheritance of acquired charac-
teristics, with evolution conceived of as a progressive, purposeful process
tending toward ever-increasing perfection.
• 1859 to 1909: Darwinian evolution by natural selection, eventually
replaced by evolution by Mendelian macromutation.
• 1909 to 1959: evolution by macromutation, eventually replaced by neo-
Darwinian gene-level microevolution.
• 1959 to 2009: neo-Darwinian gene-level microevolution, replaced by
multilevel selection and macroevolution via evolutionary developmen-
tal mechanisms.
In almost every case, the underlying focus has been on the “engines of
variation” and how they affect what George Gaylord Simpson called the
“tempo and mode of evolution.” Ever since Darwin first presented his theo-
ry of descent with modification, the real mystery has been where the varia-
tions that provide the raw material for evolution come from. An investiga-
tion of the multifarious sources of variation and the discovery of multiple
mechanisms of descent with modification will be the topic of the next
series of lectures in this conceptual history of the Darwinian revolutions.

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 FOR GREATER UNDERSTANDING

Questions
1. Does evolution proceed at different rates and via different mechanisms?
2. What were the main tenets of the “modern evolutionary synthesis”?
3. What has happened to the “modern evolutionary synthesis” over the
past half century?

Suggested Readings
Simpson, George Gaylord. Tempo and Mode in Evolution. New York:
Columbia University Press, 1984 (1944).

Other Books of Interest

Mayr, Ernst, and William B. Provine. The Evolutionary Synthesis:
Perspectives on the Unification of Biology. Cambridge, MA: Harvard
University Press, 1998 (1980).
Rensch, Bernhard. Evolution Above the Species Level. New York: Columbia
University Press, 1970.
Stebbins, G. Ledyard. Variation and Evolution in Plants. New York:
Columbia University Press, 1967.

Recorded Books
Sengoopta, Chandak. Darwin, Darwinism, and the Modern World.
The Modern Scholar Series. Prince Frederick, MD: Recorded
Books, LLC, 2004.

Websites of Interest
1. Allen MacNeill provides an entry on the Evolutionary Psychology blog
entitled “The Modern Evolutionary Synthesis.” —
http://evolpsychology.blogspot.com/2009/03/
modern-evolutionary-synthesis.html
2. A Facebook “Interest” page on modern evolutionary synthesis. —
https://www.facebook.com/pages/Modern-evolutionary-
synthesis/108410322522628/
3. The BioMed Central website provides a PDF of a paper by Michael R.
Rose and Todd H. Oakley entitled “The New Biology: Beyond the
Modern Synthesis.” —
http://www.biology-direct.com/content/pdf/1745-6150-2-30.pdf

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 COURSE MATERIALS
Suggested Readings
Bowler, Peter J. The Eclipse of Darwinism: Anti-Darwinian Evolution
Theories in the Decades Around 1900. Baltimore: The Johns Hopkins
University Press, 1992 (1983).
Burtt, Edwin Arthur. The Metaphysical Foundations of Modern Physical
Science: A Historical and Critical Essay. Charleston, SC: BiblioBazaar,
2009 (1924).
Dawkins, Richard. The Blind Watchmaker: Why the Evidence of Evolution
Reveals a Universe without Design. New York: Penguin, 2006.
Dennett, Daniel C. Darwin’s Dangerous Idea: Evolution and the Meanings
of Life. New York: Simon & Schuster, 1996.
Fisher, Ronald Aylmer. The Genetical Theory of Natural Selection.
Charleston, SC: Nabu Press, 2010.
Haldane, J.B.S. The Causes of Evolution. Princeton: Princeton Science
Library, 1990.
Kevles, Daniel J. In the Name of Eugenics: Genetics and the Uses of
Human Heredity. Cambridge, MA: Harvard University Press, 1998.
Larson, Edward J. Evolution: The Remarkable History of a Scientific Theory.
New York: Modern Library, 2006.
Mayr, Ernst. The Growth of Biological Thought: Diversity, Evolution, and
Inheritance. Cambridge, MA: Belknap Press of Harvard University
Press, 1985.
———. What Evolution Is. New York: Basic Books, 2002.
Popper, Karl R. The Logic of Scientific Discovery. 2nd ed. New York:
Routledge, 2002.
Provine, William B. The Origins of Theoretical Population Genetics.
Chicago: University of Chicago Press, 2001 (1971).
Scott, Eugenie C. Evolution vs. Creationism: An Introduction. 2nd ed.
Berkeley: University of California Press, 2009.
Simpson, George Gaylord. Tempo and Mode in Evolution. New York:
Columbia University Press, 1984 (1944).
Other Books of Interest
Black, Edwin. War Against the Weak: Eugenics and America’s Campaign to
Create a Master Race. New York: Dialog Press, 2008.
Dennett, Daniel C. Freedom Evolves. New York: Penguin, 2004.
Dobzhansky, Theodosius. Genetics and the Origin of Species. New York.
Columbia University Press, 1982 (1937).

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Feyerabend, Paul. Against Method. 4th ed. New York: Verso Books, 2010.
Futuyma, Douglas. Evolution. 2nd ed. Sunderland, MA: Sinauer
Associates, 2009.
Gould, Stephen J. The Mismeasure of Man. New York: W.W. Norton &
Co., 1996.
Hofstadter, Richard. Social Darwinism in American Thought. Boston:
Beacon Press, 1992 (1944).
Kuhn, Thomas S. The Structure of Scientific Revolutions. 3rd ed. Chicago:
University of Chicago Press, 1996.
Larson, Edward J. The Creation-Evolution Debate: Historical Perspectives.
Athens, GA: University of Georgia Press, 2007.
Mayr, Ernst. Systematics and the Origin of Species from the Viewpoint of a
Zoologist. Cambridge, MA: Harvard University Press, 1999 (1942).
Mayr, Ernst, and William B. Provine. The Evolutionary Synthesis:
Perspectives on the Unification of Biology. Cambridge, MA: Harvard
University Press, 1998 (1980).
Miller, Kenneth R. Finding Darwin’s God: A Scientist’s Search for Common
Ground Between God and Evolution. New York: Harper Perennial, 2007.
National Academy of Sciences. Teaching about Evolution and the Nature of
Science. Washington, DC: National Academies Press, 1998.
Pirsig, Robert M. Zen and the Art of Motorcycle Maintenance: An Inquiry
into Values. New York: Harper Perennial, 2008.
Popper, Karl. The Open Society and Its Enemies: Volume One: The Spell of
Plato. 7th ed. New York: Routledge, 2002 (1971).
Rensch, Bernhard. Evolution Above the Species Level. New York: Columbia
University Press, 1970.
Ruse, Michael. Darwin and Design: Does Evolution Have a Purpose?
Cambridge, MA: Harvard University Press, 2004.
———. The Darwinian Revolution: Science Red in Tooth and Claw.
Chicago: University of Chicago Press, 1979.
Schrödinger, Erwin. “The Ionian Enlightenment.” Pp. 53–68. Nature and
the Greeks and Science and Humanism. Cambridge: Cambridge
University Press, 1996.
Stebbins, G. Ledyard. Variation and Evolution in Plants. New York:
Columbia University Press, 1967.
Thompson, Keith Stewart. Before Darwin: Reconciling God and Nature.
New Haven: Yale University Press, 2005.
Wilson, Edward O. Consilience: The Unity of Knowledge. New York:
Vintage, 1999.

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Zimmer, Carl. Evolution: The Triumph of an Idea. New York: Harper
Perennial, 2006.
Recorded Books
Dyer, Betsey Dexter. The Basics of Genetics. The Modern Scholar Series.
Prince Frederick, MD: Recorded Books, LLC, 2009.
Sengoopta, Chandak. Darwin, Darwinism, and the Modern World.
The Modern Scholar Series. Prince Frederick, MD: Recorded
Books, LLC, 2004.
These books are available online through www.modernscholar.com
or by calling Recorded Books at 1-800-636-3399.

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 RECORDED BOOKS
The study of the natural sciences is among the most popular course topics in col-
leges and universities around the world. The Modern Scholar also offers the follow-
ing courses in the natural sciences.

THE BUILDING BLOCKS OF HUMAN LIFE:

Understanding Mature Cells and Stem Cells
Professor John K. Young—Howard University College of Medicine
Every human is composed of an amazing assortment of cells and tissues
that carry out myriad functions necessary for sustaining life. In clear, concise
language, Professor Young explains the basic categories of cells and tissues and
then delves into their specialized functions, whether it be for muscle cells or
the cells of reproductive organs and the highly unusual entities known as
“extreme” cells. He then takes audiences on a fascinating journey of discovery,
where a complex scheme of activity is taking place all the time, literally just
beneath the surface.

HUMAN ANATOMY: The Beauty of Form and Function

Professor John K. Young—Howard University College of Medicine
Our bodies perform an amazing number and variety of tasks that we liter-
ally could not live without. Renowned scholar John K. Young provides a fasci-
nating look at how the human body is constructed, how it employs its different
parts to our advantage, and how it can malfunction if not properly maintained.
Professor Young describes not only the basic anatomical bones and organs that
constitute our physical form, but also the role each plays in the synchronized
effort to keep us alive.

THE BASICS OF GENETICS

Professor Betsey Dexter Dyer—Wheaton College
Professor Betsey Dexter Dyer examines the wide-ranging field of genetics,
which is the study of the hereditary information of organisms, how it is used, and
how it is transferred through generations. These fascinating lectures also address
DNA sequences and how they apply to “genetic engineering,” viruses, and
genetic diseases such as cancers and birth defects. In addition to examining why
people look and act the way they do, the course also considers the philosophical
issues associated with such controversial topics as cloning and genetic ID cards.

FUELING THE PLANET: The Past, Present, and Future of Energy

Professor Michael B. McElroy—Harvard University
Renowned professor Michael B. McElroy leads a comprehensive examina-
tion of energy, including its history, use in the world today, and environmental
consequences. Whether discussing the “oil shocks” of the 1970s, the current
reliance on imported oil, or the growing buildup of carbon dioxide in the plan-
et’s atmosphere, it is clear that energy represents one of the world’s most daunt-
ing challenges. In these informed, easy-to-follow lectures, Professor McElroy
imparts a clear understanding of energy—in all its applications—and offers a
vision for a clean, safe, and sustainable future.

These courses are available online through www.modernscholar.com

or by calling Recorded Books at 1-800-636-3399.

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