Evolution

Learning Goals
► 1. Define "Evolution" & "Natural Selection".
► 2. Describe the 4 steps of Natural Selection,
giving an example of each.
► 3. Explain the importance of "Variation".
► 4. Does Natural Selection act on an organism
phenotype or genotype? Explain!
► 5. List the 5 evidences that support the
Theory of Evolution.
 What do you think of when you hear the word

“EVOLUTION”
Science? Animals?

Evolution is a very complex and controversial issue. This lesson is an

introduction to the theory of evolution and natural selection as Humans?
Change? presented
by Charles Darwin

Charles
Darwin?

Religion?
Survival? Fossils?
Extinction?
Charles Darwin (1809-1882)
► He was an English Naturalist
► He traveled around the world on his
ship, the Beagle
► Studied species and fossils in the
Galapagos Islands and around the
world
► Why did some species survive while
others became extinct?
► Natural selection
► Published The Origin of Species in
1859
 Darwin’s Theory
► Darwin's theory of evolution has four main parts:

 Organisms have changed over time, and the ones living today are different from
those that lived in the past. Furthermore, many organisms that once lived are
now extinct. The world is not constant, but changing.

 Change is gradual and slow, taking place over a long time. This was supported
by the fossil record, and was consistent with the fact that no naturalist had
observed the sudden appearance of a new species.

 All organisms come from common ancestors by a process of branching. Over

time, populations split into different species, which are related because they are
descended from a common ancestor. Thus, if one goes far enough back in time,
any pair of organisms has a common ancestor. This explained the similarities of
organisms that were classified together -- they were similar because of shared
traits inherited from their common ancestor. It also explained why similar species
tended to occur in the same geographic region.

 The mechanism of evolutionary change is natural selection.

► Darwin’s Theory of Natural Selection
occurs in four steps:
 Overproduction
 Variation
 Competition
 Selection
 1. Overproduction
► Each species produces more offspring
that can survive
 Which community has a better
chance of surviving a natural
disaster?
Community A Community B
 2. Variation

► Each individual has a

unique combination
of inherited traits.
► Adaptation: an
inherited trait that
increases an
organism’s chances of
survival
What adaptations do
you see?
What adaptations do
you see?
 Why is Variation Important?
► Because the environment changes.
► The more variation within a species,
the more likely it will survive
 EX: If everyone is the same, they are all
vulnerable to the same environmental
changes or diseases
► Themore variation of types of species
in an habitat, the more likely at least
some will survive
 EX: Dinosaurs replaced by mammals
 Peppered Moth
A

► Which moth will the bird catch?

B
3. Competition

► Individuals COMPETE for limited

resources:
 Food, water, space, mates
► Naturalselection occurs through
“Survival of the fittest”
► Fitness:
the ability to survive long
enough to reproduce
► Notall individuals survive to
adulthood
 4. Selection
► Theindividuals with the best traits /
adaptations will survive and have the
opportunity to pass on it’s traits to
offspring.
 Natural selection acts on the phenotype
(physical appearance), not the genotype
(genetic makeup)
 Ex: When a predator finds its prey, it is
due to the prey’s physical characteristics,
like color or slow speed, not the alleles
(BB, Bb)
► Individuals with traits that are not
well suited to their environment either
die or leave few offspring.
► Evolution occurs when good traits
build up in a population over many
generations and bad traits are
eliminated by the death of the
individuals.
 Natural Selection
► “I have called this principle, by which each slight
variation, if useful, is preserved, by the term of
natural selection.”
– Charles Darwin - The Origin of Species

► Darwin's theory of natural selection holds that

variation within species occurs randomly and that
the survival or extinction of each organism is
determined by that organism's ability to adapt to
its environment.
On The Galapagos Islands
► Darwin found mockingbirds that were similar to ones that were native
to Chile, but differed slightly from island to island
► He studied different species of finches and the slight variations in their
beaks
► He noticed that the shapes of tortoise shells also varied slightly from
island to island
► He found fossils of animals that had recently become extinct
► He kept a journal and collected fossils and specimens for further study
Darwin’s Finches

► These are some of the finches

that Darwin studied on his
voyage
► Though they are all finches,
their beaks distinguish them
from one another
► Some finches developed short,
strong beaks that made it
possible for them to crack nuts
► Some developed long, fine
beaks to reach insect larvae in
tiny holes
► This is an example of how these
finches adapted to their
environment to survive (natural
selection)
 Darwin’s Finches

Darwin believed that all of the different finches came from a common ancestor
and that their differences were a result of natural selection
 Example of Natural Selection
Peppered Moth
 Moths can camouflage with trees to avoid
being eaten by birds.
► There were light moths and dark moths living
near English industrial cities in the 19th century
 The dark moths stood out on the light
colored trees and were more likely to be seen
and eaten by birds
► Thus, there were many more light
colored moths than dark colored moths.

► As English factories produced more and more

soot, the trees turned a darker color. This was Because the dark moth was able to
able to camouflage the dark moths, but not the camouflage it was able to avoid
light moths being eaten.
 THEN, the light moths stood out on the dark
trees and were more likely to be seen and If the light colored moth is not
eaten by birds! able to adapt to its environment
then it will eventually become
► Thus, there were more dark colored
extinct.
moths than light colored moths.
►
Camouflage
Many animals have evolved to resemble the environment around them.
► This makes it very difficult for predators to find them and eat them, thus increasing their
chance of survival. It also makes it easier for predators to sneak up on prey.
► Can you spot them?
Stick Bug Large Fly Preying Mantis
Brimstone Butterfly

Camo Moth Lion Seal

 Patterns of Evolution
► Darwin believed that natural selection can
ultimately lead to the formation of new
species.
► Sometimes many species evolve from a
single ancestral species.
► Similarities in skeletal and muscular
structure of Hawaiian honeycreepers led
scientists to conclude that the 23 species
of honeycreepers evolved from one
ancestral species.
► Such an evolutionary pattern, in which
many related species evolved from a
single ancestral species, is called adaptive
radiation.
Adaptive Radiation
► Adaptive radiation most
commonly occurs when
a species of organisms
successfully invades an
isolated region where
few competing species
exist. If new habitats
are available, new
species will evolve.
 Divergent Evolution
Red Fox
► Divergent evolution is the process of two or
more related species becoming more and
more dissimilar.
► Example: The red fox and the kit fox
 The red fox lives in mixed farmlands and
forests, where its red color helps it blend in
with surrounding trees.
 The kit fox lives on the plains and in the
deserts, where its sandy color helps conceal
Kit Fox it from prey and predators. The ears of the
kit fox are larger than those of the red fox.
The kit fox's large ears are an adaptation to
its desert environment
► Similarities in structure indicate that the red
fox and the kit fox had a common ancestor.
As they adapted to different environments,
the appearance of the two species
diverged, or became more and more
different.
Convergent Evolution
 Convergent Evolution
► Convergent evolution is the opposite of divergent
evolution
► In convergent evolution, unrelated species become more
and more similar in appearance as they adapt to the
same kind of environment.
► Frogs and Chameleons are examples of convergent
evolution because although they are different
amphibians, they have both developed harpoon-like
tongues to catch insects
 Co-evolution
► Co-evolution is the joint change of two or more
species in close interaction. Predators and their prey
sometimes co-evolve; parasites and their hosts often
co-evolve; plant-eating animals and the plants upon
which they feed also co-evolve.

► One example of co-evolution is pollination of orchids

by African moths.

 These species co-evolve because the moths depend on

the flowers for nectar, and the flowers depend on the
moths to spread their pollen so that they can reproduce.

► The relationship between the moth and the orchids is

mutually beneficial because they help each other
survive.
Why is This Important?
► Divergent, convergent and co-evolution are
different ways organisms adapt to the
environment. These are examples of how
the diversity of life on earth is due to the
ever-changing interaction between a species
and its environment.
 Extinction
► Extinction is the disappearance of an entire species
► If a species does not have the genetic traits to survive in its
environment, then the species will eventually become extinct forever
► Some examples of extinct animals are:

Galapagos Tortoise Dinosaurs Steller’s Sea Cow Laughing Owl

Bali Tiger Thylacine Quagga Dodo Bird

Reasons for Extinction
► Rarity- when there are very few animals of a species left
(Galapagos Tortoise)
► Inbreeding- when animals mate too much within their own
group the offspring become less able to survive and adapt
in a healthy way
► Hybridization-When two animals from different sub-species
mate, they might pass on genes that are less healthy
(Quagga-half horse half zebra)
► Gradual loss of habitat- When an animal's habitat is slowly
destroyed and they have nowhere to live. (Bali Tiger)
► Long-term environmental trends- Scientists think that
dinosaurs became extinct because of a slow cooling of the
earth
Reasons for Extinction
► Catastrophe- Volcanic eruption, dramatic change in climate, tsunami,
etc.
► Extinction or reduction of mutualistic population- If two species are
dependent on each other, then the endangering of one also endangers
the other
► Competition- When a new species is introduced to a habitat, then the
stronger of the two species will be more likely to survive.
► Predators-When the population of a species of predator in a habitat
suddenly increases, the population of their prey decreases
► Disease- If a particular sickness spreads quickly throughout a particular
species, then many may die before they can reproduce
► Hunting and collecting- Hunters have been largely responsible for the
endangerment of many animal species.
 Applications
► Knowledge about evolution and natural selection
has benefited our society in many ways, and has
helped make numerous technological advances,
especially in the field of biology and medicine
 Using Darwin’s theory of natural selection, scientists
have been able to identify the desirable traits which
would improve the probability of survival in certain
species
 It has helped scientists and doctors in treating viruses
and diseases.
 FOR EXAMPLE
► Did you know that when a doctor gives you antibiotics, you need to
continue taking them until all of the pills are gone, even if you start to
feel better? When a doctor gives you antibiotics, they start to fight of
the bacteria in your body, little by little. It starts with the weak
bacteria, and eventually kills the strongest bacteria.
► BUT, if you stop taking your medicine, then it is only the STRONG
bacteria that are left in your body. That means that they will continue
to reproduce and become stronger and stronger, and it will be much
harder for the medicine to kill them. This is an example of natural
selection because the strong bacteria survives and grows.
 Conclusion

► Darwin’s observations have

made a great impact in the
scientific community. Because
of his observations, we are
better able to understand why
some species survive and
some die.

► We are also better able to

take precautions to protect
species that are endangered.

► Lastly, we can understand the

diversity in the world around
us and learn to appreciate it.
 References
► http://www.lucidcafe.com/library/96feb/darwin.html

► http://outreach.mcb.harvard.edu/teachers/Summer06/BethMick/TheoryEvolution.ppt#264,9,EVID
ENCE OF EVOLUTION

► wikipedia.com

► http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html

► http://people.rit.edu/rhrsbi/GalapagosPages/DarwinFinch.html

► http://bioweb.cs.earlham.edu/9-12/evolution/HTML/converge.html

► http://biol1114.okstate.edu/study_guides/scenarios/5-galapagos/images/adaptive_radiation.gif

► http://en.wikipedia.org/wiki/List_of_examples_of_convergent_evolution#Reptiles

► http://www.pbs.org/wgbh/evolution/extinction/index.html

► http://images.google.com/imgres?imgurl=http://sciencegnus.com/Quagga.jpg&imgrefurl=http://s
ciencegnus.com/Extinct%2520Animals.html&usg=__jvKRAbOBBqLDKizo6r_GeeZqXo8=&h=301&w
=400&sz=10&hl=en&start=1&um=1&tbnid=XgWOxV3IPxCzGM:&tbnh=93&tbnw=124&prev=/ima
ges%3Fq%3Dextinct%2Banimals%26hl%3Den%26rls%3Dcom.microsoft:en-us%26um%3D1

► http://library.thinkquest.org/J002558F/extinction.htm