Topic 1: Understanding Evolution • Can be understood by function

• Develop to reach potential given

•Earth has millions of other kinds of
to them by maker
organisms of every imaginable shape, size,
and habitat. Georges-Louis Leclerc Comte de Buffon
(1749-1788)
•This variety of living things is called
biological diversity. • Different geographical locations
have different organisms
Evolutionary biology seeks to explain the
• Hypothesized that all
diversity of life: the variety of organisms
quadrupeds are descended from
and their characteristics, and their changes
just 38 species
over time.
• Darwin: “the first author who in
History of Evolutionary Thought modern times has treated it
(evolution) in a scientific spirit
Aristotle was Buffon. But as his opinions
fluctuated greatly at different
• Developed the scientific method
periods, and as he does not enter
• Interested in identifying the
on the causes or means of the
difference between living (biotic)
transformation of species”.
and nonliving (abiotic) things
• First detailed recordings of James Hutton (1795)
zoology
-Study of animals • “Father of Geology”
-Dissections • Prevailing idea: catastrophism –
-Observtions of habitats changes were due to large, quick
events
A History of Evolution • Uniformitarianism – Geology
was a long process with small
Plato (450-350BC)
changes over time
• Species were static and
Jean Baptiste Lamarck (1744-1829)
unchanging
• New sciences emerge: Geology
Ladder of Life
and Paleontology
• Wanted to identify relationships -Lamarck sees relationships and
and hierarchy of life changes in fossil record
• All life on Earth was introduced • Creates the best accepted
by a divine creator evolutionary theory of its time,
-Life forms do not change over often referred to as
time “Lamarckism”
• Did not have knowledge of fossil
Lamarckism & “Inner Need”
records, geology, or genetics
• Noted changes in physical
Structure and Form
characteristics over time
 • Identified that traits were passed Saw that certain species had
on to offspring similar and dissimilar traits based
• Believed traits were acquired on environment
based on “Inner Needs” of an -Suggested that not all organisms
organism in nature are created as equal

A Travel to the Galapagos

• Saw great diversity in living

things
• Collected samples of a variety of
species
• Noticed “Struggle to Survive”

Environment Influences Traits

• Organisms best suited for their

Or in other words… environment are more likely to
pass on their traits
• All organisms have evolved from
a common ancestor

Charles Lyell (1830-1833)

• Geologist, followed footsteps of

Hutton
• Earth was over 300 million years
old
• BFFs with Darwin

Alfred Russel Wallace

Lamarck Was Wrong
• Independently came up with the
idea of natural selection
• Sent his ideas to Darwin in 1858
(who already had same ideas)

Charles Darwin (1809-1882)

• “A disturbed young man who

would not accomplish anything” Adaptations
• Developed the basis for today’s
evolutionary theory
-Studies the form and function of
organisms
 Early Ideas About Evolution

Early scientists proposed ideas about

evolution

• Evolution is the biological change

process by which descendants
come to differ from their
ancestors.
• A species is a group of organisms
that can reproduce and have
fertile offspring.
-Horse Ancestor (55MYA)
• There were many important
naturalists in the 18th century.
-Linnaeus: classification system
A Brief Summary
from kingdom to species
• Darwin founded the Theory of -Buffon: species shared
Evolution as we know it ancestors rather than arising
• Common ancestor separately.
-Descent with modification -E. Darwin: more complex forms
developed from less-complex
• Physical modifications come
forms
from:
-Lamarck: environmental change
-Sexual Reproduction
leads to use or disuse of a
-Genetic Mutation
structure
• Survival of the Fittest
-Struggle for Survival Theories of geologic change set the stage
-Adaptations for Darwin’s theory
• Reproduction and passing on of
traits to offspring • Catastrophism
Natural disasters such as floods
and volcanic eruptions have
shaped landforms and caused
species to become extinct
• Gradualism
Changes in landforms resulted
from slow changes over a long
period of time
• Uniformitarianism
The geologic processes that
shape Earth are uniform through
time
 • Uniformitarianism is the Voyage of Beagle
prevailing theory of geologic
Dates: February 12, 1831
change.
Every layer of rock was formed by Naturalist: Charles Darwin
the uniform laying down of
sediment that still occurs today. Ship: H.M.S. Beagle

Destination: Voyage around the world

Charles Darwin Findings: evidence that propose a

revolutionary hypothesis about how life
Born: February 12, 1809 changes over time
Birthplace: The Mount, Shrewsbury, Patterns of Diversity
England
• Darwin visited Argentina and
Died: April 19, 1882 Australia which had similar
Location of death: Down House, Down, grassland ecosystems.
Kent, England -those grasslands were inhabited
by very different animals.
Cause of death: Unspecified -neither Argentina and Australia
was home to the sort of animals
Remains: Buried, Westminster Abbey, that lived in European
London, England grasslands.
Darwin’s Theory of Evolution • Darwin posed challenging
questions.
• Evolution, or change over time, is -Why were there no rabbits in
the process by which modern Australia, despite the presence
organisms have descended from of habitats that seemed perfect
ancient organisms. for them?
• A scientific theory is a well- -Why were there no kangaroos in
supported testable explanation England
of phenomena that have
Living Organisms and Fossils
occurred in the natural world.

Voyage of the H.M.S. Beagle • Darwin collected the preserved

remains of ancient organisms,
called fossils.
• Some of those fossils resembled
organisms that were still alive
today.
• Others looked completely unlike
any creature he had ever seen.
• As Darwin studied fossils, new
questions arose.
 -Why had so many of these • Darwin Observed that
species disappeared? characteristics of many plants
-How were they related to living and animals vary greatly among
species? the islands
• Hypothesis: Separate species
The Galapagos Island
may have arose from an original
• The smallest, lowest islands were ancestor
hot, dry, and nearly barren-Hood Ideas that shaped Darwin’s Thinking
Island-sparse vegetation
• The higher islands had greater • James Hutton:
rainfall and a different • 1795 Theory of Geological
assortment of plants and change
animals-Isabela-Island had rich -Forces change earth’s surface
vegetation. shape
• Darwin was fascinated in -Changes are slow
particular by the land tortoises -Earth much older than
and marine iguanas in the thousands of years
Galápagos.
Charles Bonnet
• Giant tortoises varied in
predictable ways from one island • Born: 13-Mar-1720
to another. Birthplace: Geneva, Switzerland
• The shape of a tortoise's shell Died: 20-May-1793
could be used to identify which Location of death: Switzerland
island a particular tortoise Cause of death: unspecified
inhabited. • Gender: Male
Race or Ethnicity: White
Occupation: Naturalist,
Philosopher
• Nationality: Switzerland
Executive summary: Discovered
parthenogenesis

Ideas that Shaped Darwin’s Thinking

• Charles Lyell
-Book: Principles of Geography
Animals found in the Galapagos • Geographical features can be
built up or torn down
• Land Tortoises • Darwin thought if earth changed
• Darwin Finches over time, what about life?
• Blue-Footed Booby
• Marine Iguanas Jean Baptiste Lamarck 1744-1829

The Journey Home Lamarck’s Contribution

 • Jean Baptiste Lamarck was the -Food runs out
first to coin the term “Biology” in -Darwin applied this theory to
1802. animals
• He believed that this term would
John Stevens Henslow (1796-1861)
permit botanists and zoologists
to share, what life had in • Henslow was a formative
common. influence on Charles Darwin,
• 14 August 1809, presented the who described their meeting as
two volumes of his most the one circumstance which
important book, Philosophie influenced his career more than
Zoologique, to France's Institute any other.
National des Sciences et Arts. • Their friendship persisted to the
• Twenty years later, he died end of Henslow's life.
penniless, blind and scorned,
surrounded by hundreds of Alfred Russell Wallace
unsold copies of his book.
• Born: January 8, 1823
• He was buried in a rented plot,
exhumed and 'dispersed' five • Birthplace: Great Britain
years later • Died: November 7 1913
• Location of death: England
Lamarck’s Theory of Evolution • Cause of death: unspecified
• Co-Discovered Theory of
• Tendency toward Perfection
Evolution
(Giraffe necks)
• Use and Disuse (bird’s using Publication of Origin of Species
beaks)
• Inheritance of Acquired Traits • Russell Wallace wrote an essay
summarizing evolutionary
change from his field work in
Malaysia
• Gave Darwin the drive to publish
his findings

Natural Selection & Artificial Selection

• Natural Selection--differences
among individuals of a species
• Artificial selection- nature
provides the variation among
Population Growth
different organisms, and humans
• Thomas Malthus19th century select those variations they find
English economist useful.
• If population grew (more Babies
Evolution by Natural Selection
born than die)
-Insufficient living space
 • The Struggle for Existence- Evidence for Evolution
members of each species have to
• The Fossil Record - Layer show
compete for food, shelter, other
life necessities change
• Geographic Distribution of Living
• Survival of the Fittest-Some
Things - similar environments
individuals better suited for the
have similar types of organisms
environment are the ones the
• Homologous Body Structures
can pass their lucky genes (DNA)
• Similarities in Early Development
Struggle For Existence & Survival of The
Homologous Structures
Fittest
Homologous Structures-structures that
have different mature forms in different
organisms, but develop from the same
embryonic tissue.

Natural Selection

• Over time, natural selection

results in changes in inherited
characteristics of a population.
• These changes increase a species
fitness in its environment
Evidence for Evolution

• Vestigial organs-organs that

serve no useful function in an
organism
• Examples:
-appendix, miniature legs, arms
• Flightless Cormorant

Descent

• Descent with Modification - Each

living organism has descended,
with changes from other species
over time
• Common Descent - were derived Similarities in Early Development
from common ancestors
Summary of Darwin’s Theory understand what geochemical conditions
nurtured the first life forms. What water,
• Individuals in nature differ from chemistry and temperature cycles fostered
one another the chemical reactions that allowed life to
• Organisms in nature produce emerge on our planet? Because life arose
more offspring than can survive, in the largely unknown surface conditions
and many of those who do not of Earth’s early history, answering these
survive do not reproduce. and other questions remains a challenge.
• Because more organisms are
produce than can survive, each When did life on Earth begin?
species must struggle for
*Earth is about 4.5 billion years old.
resources
Scientists think that by 4.3 billion years ago,
• Each organism is unique, each
Earth may have developed conditions
has advantages and
suitable to support life. The oldest known
disadvantages in the struggle for
fossils, however, are only 3.7 billion years
existence
old. During that 600 million-year window,
• Individuals best suited for the
life may have emerged repeatedly, only to
environment survive and
be snuffed out by catastrophic collisions
reproduce most successful
with asteroids and comets.
• Species change over time
• Species alive today descended Zircons, highly durable minerals that
with modification from species formed in magma.
that lived in the past
• All organisms on earth are united *The details of those early events are not
into a single family tree of life by well preserved in Earth’s oldest rocks.
common descent Some hints come from the oldest zircons,
highly durable minerals that formed in
magma. Scientists have found traces of a
form of carbon—an important element in
living organisms—in one such 4.1 billion-
year-old zircon. However, it does not
provide enough evidence to prove life’s
existence at that early date.

Where did life on Earth begin?

Volcanically Active Hydrothermal

Environments
Topic 2: Origin of Life
*Some microorganisms thrive in the
*The origin of life on Earth stands as one of scalding, highly acidic hot springs
the great mysteries of science. Various environments like those found today in
answers have been proposed, all of which Iceland, Norway and Yellowstone National
remain unverified. To find out if we are Park. The same goes for deep-sea
alone in the galaxy, we will need to better hydrothermal vents. These chimney-like
vents form where seawater comes into nitrogen. These elements become solid
contact with magma on the ocean floor, only under very cold temperatures, such as
resulting in streams of superheated exist in the outer solar system, not nearer
plumes. The microorganisms that live near to the sun where Earth is. Also, carbon, like
such plumes have led some scientists to gold, is rare at the Earth’s surface. That’s
suggest them as the birthplaces of Earth’s because carbon chemically bonds more
first life forms. often with iron than rock. Gold also bonds
more often with metal, so most of it ends
Clay Minerals up in the Earth’s core. So, how did the small
Organic molecules may also have formed in amounts found at the surface get there?
certain types of clay minerals that could Could a similar process also have unfolded
have offered favorable conditions for on other planets?
protection and preservation. This could Structure of Amino Acids
have happened on Earth during its early
history, or on comets and asteroids that *Amino acids are molecules that combine
later brought them to Earth in collisions. to form proteins. Amino acids and proteins
This would suggest that the same process are the building blocks of life. When
could have seeded life on planets proteins are digested or broken down,
elsewhere in the universe. amino acids are left. The human body uses
amino acids to make proteins to help the
What are the ingredients of life on Earth? body: Break down food.
*Sunlight provides the energy source at *The last ingredient is water. Water now
the surface, which drives photosynthesis. covers about 70% of Earth’s surface, but
On the ocean floor, geothermal energy how much sat on the surface 4 billion years
supplies the chemical nutrients that ago? Like carbon and nitrogen, water is
organisms need to live. much more likely to become a part of solid
objects that formed at a greater distance
from the sun. To explain its presence on
Earth, one theory proposes that a class of
meteorites called carbonaceous chondrites
formed far enough from the sun to have
served as a water-delivery system.

Major Scientific Theories For How Life

Emerged
*Also crucial are the elements important to
Life emerged from a primordial soup
life. For us, these are carbon, hydrogen,
oxygen, nitrogen, and phosphorus. But *The idea of the primordial soup was
there are several scientific mysteries about originally proposed by Alexander Oparin
how these elements wound up together on and John Haldane as a possible explanation
Earth. For example, scientists would not for the creation of life on our planet. The
expect a planet that formed so close to the theory states that if energy is added to the
sun to naturally incorporate carbon and gases that made up Earth's early
atmosphere, the building blocks of life *The panspermia theory argues that life is
would be created. originated in space, in spatial ices, and
continuously distributed to the planets by
As a University of Chicago graduate student comets and meteorites.
in 1952, Stanley Miller performed a famous
experiment with Harold Urey, a Nobel Meteorites then might have served as the
laureate in chemistry. Their cosmic Mayflowers that transported
results explored the idea that life formed in molecular seeds to Earth. In 1969, the
a primordial soup. Murchison meteorite that fell in Australia
contained dozens of different amino
acids—the building blocks of life.

Comets

*Comets may also have offered a ride to

Earth-bound hitchhiking molecules,
according to experimental
*Miller and Urey injected ammonia, results published in 2001 by a team of
methane and water vapor into an enclosed researchers from Argonne National
glass container to simulate what were then Laboratory, the University of California
believed to be the conditions of Earth’s Berkeley, and Lawrence Berkeley National
early atmosphere. Then they passed Laboratory. By showing that amino acids
electrical sparks through the container to could survive a fiery comet collision with
simulate lightning. Amino acids, the Earth, the team bolstered the idea that
building blocks of proteins, soon formed. life’s raw materials came from space.
Miller and Urey realized that this process
could have paved the way for the Meteorites
molecules needed to produce life. *In 2019, a team of researchers in France
Scientists now believe that Earth’s early and Italy reported finding extraterrestrial
atmosphere had a different chemical organic material preserved in the 3.3
makeup from Miller and Urey’s recipe. billion-year-old sediments of Barberton,
Even so, the experiment gave rise to a new South Africa. The team suggested
scientific field called prebiotic or abiotic micrometeorites as the material’s likely
chemistry, the chemistry that preceded the source. Further such evidence came in
origin of life. This is the opposite of 2022 from samples of asteroid Ryugu
biogenesis, the idea that only a living returned to Earth by Japan’s Hayabusa2
organism can beget another living mission. The count of amino acids found in
organism. the Ryugu samples now exceeds 20
different types.
Topic 3: Species Concepts and Attributes

WHAT IS A SPECIES???

Loop hole = Asexual reproduction and

fossils

PROBLEMS WITH THE BIOLOGICAL SPECIES

CONCEPT
*Homo sapiens, (Latin: “wise man”) the • Difficult to apply to fossils
species to which all modern human beings
• Asexual organisms don’t fit the
belong.
criteria

*Phylogeny can be described

as the relationship between all
the organisms on Earth that have
Certainly, no clear line of demarcation has descended from a common
yet been drawn between species and sub- ancestor, whether they are
species – that is, the forms which…come extinct or extant.
very near to, but do not quite arrive at, the
rank of species. …A well-marked variety
may therefore be called an incipient
species. …From these remarks, it will be
seen that I look at the term species as one
arbitrarily given.

Darwin, The Origin of Species

*Same as morphological A species is a group of individuals capable
of interbreeding to produce fertile
offspring.

• Biological species concept –

Species Concepts Organisms of the same spp. can
interbreed to produce viable and
• Biological Species Concept fertile offspring only w/ their
-Reproductive Isolation own spp. Ernst Mayr
-Not necessarily easy to apply
Other concepts that emphasize
• Morphological Species Concept
similarities w/in a spp.
-Phenotypic differences (fossil
species) • Morphological Spp. Concept –
• Recognition Species Concept orangizes spp. by body shape &
-Mating recognition other structural features
• Cohesion Species Concept
-Persistence of discrete • Ecological species concept –
phenotypes categorizes species based on its
• Ecological Species Concept ecological niche – role in the
-Filling of ecological niches environment
-Competition for resources
-Can be used for asexual
• Evolution Species Concept
reproduction
-Evolutionary lineages
• Pluralistic Species Concept • Phylogenetic species concept –
-Combinations of above as determines a species based on
appropriate molecular sequences

Speciation -Usually used to compare sister

species – species that are
Evolution creates (and destroys) new
morphologically similar
species, but …
*In ecology, the term “niche” describes the
What is a species?
role an organism plays in a community. A
species' niche encompasses both the
physical and environmental conditions it
requires (like temperature or terrain) and
the interactions it has with other species
(like predation or competition).

How Many Species Are There?

About 2 million species have been

described. Geographic Isolation

Estimates of existing species number range • Geographic isolation is the

from 4 million to 100 million (with 10-15 physical separation of members
million being a more commonly considered of a population.
upper estimate). • Geographic isolation is the
primary extrinsic isolating
How did this diversity of life come to be?
mechanism.
Speciation is an event that produces two or
more separate species from an original
species.

Species = basic unit

Continuous lineage – information passed

through genes
*Natural selection is a mechanism of
Speciation - rise of new species evolution. Organisms that are more
adapted to their environment are more
How Do Species Arise?
likely to survive and pass on the genes that
• The key to speciation is aided their success. This process causes
reproductive isolation of species to change and diverge over time.
populations.
Allopatric Speciation
• There are extrinsic and intrinsic
reproductive isolating • Allopatric (different home lands)
mechanisms. speciation occurs when
• Geographic isolation is the geographic isolation creates a
primary extrinsic reproductive reproductive barrier (an extrinsic
isolating mechanism. mechanism).
• Once a populations have been
separated, Natural Selection
 cause the two new Populations Behavioral Isolation – Even if they breed at
to genetically Diverge. the same time, they will not mate if they
are not attracted to one another.

Courtship rituals, like these, are critical for

mating within a species, but ineffective for
attracting members of other species.

Mechanical Isolation – Even if they attract

to one another, they cannot mate if they
are not physically compatible.

Two species of ground squirrel are Gametic Isolation – Even if they are
postulated to have descended from a physically compatible, an embryo will not
common ancestral population that was form if the egg and sperm do not fuse
separated by formation of the Grand properly.
Canyon.
Hybrid Inviability or Infertility – Even if
Sympatric Speciation fertilization occurs successfully, the
offspring may not survive, or if it survives,
• Sympatric speciation occurs may not reproduce (e.g., mule).
when a reproductive barrier is
created by something other than Hybrid Infertility Was the reason for
geographic isolation (intrinsic Cloning Mules
mechanisms).
Speciation Occurs at Widely Differing Rates
• Intrinsic mechanisms involve
changes to organisms that • A slow rate of speciation
prevent interbreeding. evidenced by a living horseshoe
• There are many different causes crab (13 extant species) and a
for intrinsic speciation. 300 million year-old fossil species
• A rapid rate of speciation
Many Intrinsic Reproductive Isolating
Mechanisms Drive Speciation evidenced by Galapagos finches
which have diversified into 13
Ecological Isolation - Even if they live in the species within the last 100,000
same place, they cant mate if they don’t years.
come in contact with one another.
Speciation Dynamics - Gradualism or
(different habits within an overlapping
Punctuated Equilibrium?
range)

Temporal Isolation - Even if they come in • Gradualism states that speciation

contact, they cant mate if they breed at occurs at a regular gradual rate.
different times. • Punctuated equilibrium states
that organisms evolved in a
relatively short period of time.
Short bursts.
 *Carl Linnaeus, also known after his
ennoblement in 1761 as Carl von Linné,
was a Swedish botanist, zoologist,
taxonomist, and physician who formalised
binomial nomenclature, the modern
system of naming organisms. He is known
as the "father of modern taxonomy".

How Do We Classify Organisms?

• Ideally, classification is based on

Species Come and Go establishing the evolutionary
• Best estimates from the fossil relationships between
record indicate that greater than organisms.
99% of species that have existed • The evolutionary relationship
are now extinct. between organisms is their
• A typical “lifetime” for a species phylogeny.
is about 1 million years. • Cladistics is the method of
classification based on
Classifying Life’s Rich Diversity establishing phylogenies (i.e.
getting at evolutionary
• An intrinsic reason is that relationships.
modern classification systems • Cladistics proceeds by comparing
tell who’s related to whom and shared ancestral and shared
how we all came to be. derived characters between sets
• A practical reason is that if we of organisms.
want to preserve an environment
compatible with human life, we’d
better know what’s out there.

The Linnaean Hierarchical Classification

System

The greater the number of derived

characters shared by a pair of organisms,
the closer their degree of relationship.

The closer the degree of relationship, the

closer the most recent common ancestor.
It’s Critical (and often difficult) To The pre-molecular view was that the great
Distinguish Homology from Analogy apes (chimpanzees, gorillas and
orangutans) formed a clade separate from
humans, and that humans diverged from
the apes at least 15-30 MYA.

Mitochondrial DNA, most nuclear DNA-

encoded genes, and DNA/DNA
hybridization all show that bonobos and
chimpanzees are related more closely to
humans than either are to gorillas.
Homologous structures, like the bat wing
and gorilla arm, are similar because they
are derived by modification of a shared Topic 5: Hardy–Weinberg Equillibrium
ancestral structure.
Measuring Evolution of Populations
Homology is the key to establishing
phylogenies. 5 Agents of evolutionary change

Another Set of Analogies Created by • Mutation

Convergent Evolution • Gene Flow
• Non-random mating
• Genetic Drift
• Selection

Results of Cladistic Analyses Sometimes Gene Mutation

Run Counter to Classical Classification
Mutations are changes in genetic material
Schemes
– changes in DNA code – thus a change in a
gene(s)

In gene mutations, the DNA code will have

a base (or more) missing, added, or
exchanges in a codon.

Gene Flow

Gene flow is the movement of genes into

or out of a population. (immigration and
emigration)
Cladistic analysis indicates that the
A population may gain or lose alleles
bird/crocodile pair is more closely related.
through gene flow
Which species are the closest living
relatives of modern humans?
Gene flow tends to reduce the differences Populations & gene pools
between populations because the gene
pools become more similar. Concepts

*Such movement may be due to migration • a population is a localized group

of individual organisms that reproduce in of interbreeding individuals
their new populations, or to the movement • gene pool is collection of alleles
of gametes (e.g., as a consequence of in the population
pollen transfer among plants) -remember difference between
alleles & genes!
Non-Random Mating • allele frequency is how common
is that allele in the population
Sexual selection occurs when certain traits
-how many A vs. a in whole
increase mating success.
population
*Non-random mating means that mate
Evolution of populations
selection is influenced by phenotypic
differences based on underlying genotypic Evolution = change in allele frequencies in
differences. Example of non-random a population
mating: Sexual selection. In some species,
males acquire harems and monopolize • hypothetical: what conditions
females. (Elk, elephant seals, horses, lions, would cause allele frequencies to
etc.) not change?
• non-evolving population
Genetic Drift
REMOVE all agents of evolutionary change
Random changes in allele frequency, which
usually occurs in small populations 1. very large population size (no
genetic drift)
Natural Selection 2. no migration (no gene flow in or
out)
A mechanism of evolution. It ensures that
3. no mutation (no genetic change)
only the traits that helps a species survive
4. random mating (no sexual
and reproduce get passed on to future
selection)
generations.
5. no natural selection (everyone is
• Survival of the Fittest equally fit)
Competition between two
Hardy-Weinberg Principle
individual organisms
• Natural Selection A mathematical model used to calculate
Survival of the fittest on a larger the allele frequencies of traits with
scale. It involves entire dominant and recessive alleles. The model
populations. assumes that the population:
• Evolution
Consequence of natural • is large
selection over thousands of • has random mating
years. • is experiencing no selection
 • has no mutation, emigration or Counting Individuals
immigration
• frequency of homozygous
If these assumptions are met then the dominant: p x p = p2
allele frequencies of the population will • frequency of homozygous
remain stable over time. recessive: q x q = q2
• frequency of heterozygotes: (p x
Hardy-Weinberg equilibrium
q) + (q x p) = 2pq
• Hypothetical, non-evolving -frequencies of all individuals
population must add to 1 (100%), so:
-preserves allele frequencies p2 + 2pq + q2 = 1
• Serves as a model (null H-W formulas
hypothesis)
-natural populations rarely in H- • Alleles: p + q = 1
W equilibrium • Individuals: p2 + 2pq + q2 = 1
-useful model to measure if
forces are acting on a population Using Hardy-Weinberg equation
-measuring evolutionary change
population:
*G.H. Hardy (the English mathematician) 100 cats
and W. Weinberg (the German physician)
84 black, 16 white
independently worked out the
mathematical basis of population genetics How many of each genotype?
in 1908. Their formula predicts the
expected genotype frequencies using the q2 (bb): 16/100 = .16
allele frequencies in a diploid Mendelian
q (b): √.16 = 0.4
population. They were concerned with
questions like "what happens to the p (B): 1 - 0.4 = 0.6
frequencies of alleles in a population over
time?" and "would you expect to see alleles p2=.36
disappear or become more frequent over
2pq=.48
time?"
q2=.16
Hardy-Weinberg theorem
Must assume population is in H-W
Counting Alleles
equilibrium!
• assume 2 alleles = B, b
• frequency of dominant allele (B)
=p
• frequency of recessive allele (b) =
q
-frequencies must add to 1
(100%), so:
p+q=1
Sampled data 1: Why is the Hs allele maintained at such high
levels in African populations?
1. Hybrids are in some way weaker.
*Sickle Cell:
2. Immigration in from an external
population that is predomiantly In tropical Africa, where malaria is
homozygous B common, the sickle-cell allele is both an
advantage & disadvantage. Reduces
3. Non-random mating... white cats infection by malaria parasite.
tend to mate with white cats and
black cats tend to mate with Cystic fibrosis:
black cats.
Cystic fibrosis carriers are thought to be
Sampled data 2: more resistant to cholera:

1. Heterozygote advantage. 1:25, or 4% of Caucasians are carriers Cc

What’s preventing this population from Malaria

being in equilibrium.
Single-celled eukaryote parasite
Application of H-W principle (Plasmodium) spends part of its life cycle in
red blood cells
Sickle cell anemia
Heterozygote Advantage
• inherit a mutation in gene coding
for hemoglobin In tropical Africa, where malaria is
-oxygen-carrying blood protein common:
-recessive allele = HsHs
-normal allele = Hb • homozygous dominant (normal)
• low oxygen levels causes -die or reduced reproduction
RBC to sickle from malaria: HbHb
-breakdown of RBC • homozygous recessive
-clogging small blood vessels -die or reduced reproduction
-damage to organs from sickle cell anemia: HsHs
• often lethal • heterozygote carriers are
relatively free of both: HbHs
Sickle cell frequency -survive & reproduce more, more
common in population
High frequency of heterozygotes
Hypothesis: In malaria-infected cells, the
• 1 in 5 in Central Africans = HbHs O2 level is lowered enough to cause sickling
• unusual for allele with severe which kills the cell & destroys the parasite.
detrimental effects in
homozygotes
-1 in 100 = HsHs
-usually die before reproductive

age