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EVOLUTION
Caution : these notes may change from the
original... They are still evolving.
SO WHAT IS EVOLUTION ANYWAY?

Definition: A change over time

More specifically: change in relative frequency
of alleles in a population
Note the word ―POPULATION”
 INDIVIDUALS DO NOT EVOLVE

SOURCES OF CHANGE



Sexual Reproduction ( Random Shuffling of
alleles)
Mutations
Geographic isolation
So, What does Darwin have to do with it?
CHARLES DARWIN
Born in England February 12, 1809 to a
wealthy family
 attended Oxford University
 became a naturalist
 joined the crew of the H.M.S. Beagle for a 5
year voyage (1831)

WHAT DARWIN LEARNED FROM THE VOYAGE

made numerous observations and collected
data that led him to propose a revolutionary
hypothesis about the way life changes
(evolution).
DARWIN’S OBSERVATIONS:
 1.

Patterns of Diversity
plants and animals are well suited to whatever
environment they inhabit
Different species live all over the world.

Ex. Argentina, Australia, and England have similar
grassland ecosystems, yet the animals inhabiting the
areas were different.
 2.
Living Organisms and Fossils
collected remains of preserved organisms called
fossils.
Some of the fossils resembled organisms that
were still alive and others looked completely
unlike any creature he had ever seen.
3. The Galapagos Islands
characteristics of many animals and plants varied
noticeably among the different Galapagos
Islands.
 Ex. The tortoises shape of the shell
corresponded to different habitats. ( Do not
write) Hood Island tortoise – long neck and
curved shell that is open and allows it reach
sparse vegetation

HOOD ISLAND ( RIGHT)

Isabela Island(below)
Pinta Island
right
OTHER ORGANISMS
noticed that the finches on the Islands all had
different beaks
 likely that a few finches founded the population
but mutations over time allowed them to eat
different foods.
 New beaks continued to be passed to the next
generation which eventually led to different
species

VARIETY OF FINCHES
Plants also undergo the same pressures of the
environment
 Variety of vegetation found based on the type
of climate that exists

NATURAL SELECTION
Definition: process by which
individuals that are better
suited to their environment
survive and reproduce most
successfully.
THE PEPPERED
MOTH
Not

a random process.
— The mutation is random, but selection acts
on that variation in a very non-random way:
genetic variants that aid survival and
reproduction are much more likely to become
common than variants that don't. Natural
selection is not random! (University of Berkeley)
ARTIFICIAL SELECTION

using genetic variation to improve crops or
livestock ; artificial selection

Artificial selection: nature provided the
variation and humans select those variations
that they found useful.
5 MAJOR POINTS TO THE NATURAL SELECTION
HYPOTHESIS
1. Genetic variations exist in populations.
Some variations are more favorable than others.
These variations are inherited.

2. Organisms produce more offspring than can
survive.
 Those that do not survive, do not reproduce.

3. Overproduction of offspring forces
competition for resources. Darwin called this
the struggle for existence.
 Not all offspring can possibly survive.


4. Individuals with favorable variations have
more ―fitness‖ ;more likely to survive and pass
those variations on to their offspring.
5. Species alive today are descended with
modification from ancestral species that lived
in the distant past.
 Darwin called this descent with modification.
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SURVIVAL OF THE FITTEST


Link to Natural Selection example cartoon
Adaptations: any inherited trait that increases the
chances of survival and reproduction of an organism.
Camouflage and Mimicry – allow animals with
successful variations survive and reproduce
 EXAMPLES IN NATURE:
Mimicry:Monarch and Viceroy, Moth and Bumblebee
Camouflage: Squirrels, Leopards, walking sticks, Praying
Mantis

WHERE’S THE PROOF?
Plentiful evidence:
 1 Fossils
 2 Geographical distribution
 3 Homology
 4. Vestigial Structures
 5 Embryology
 6 Biochemistry * (the chemistry of living
organisms)

FOSSILS
1) Fossils:
 Remnants of numerous organisms left behind
 Scientists can compare the bones of horses from
4 million years ago to ones from the present day.
 Fossils found in every layer of rock do not look the
same as those from modern life.
 The oldest fossils are more different from the
modern day organisms than the shallowest fossils


Put pictures of fossils here!
2) GEOGRAPHIC DISTRIBUTION
All over the world, there are similar animals in very
far away places.
 Animals use different adaptations to survive in
similar environments even though the
environments are separated.
 Analogous Structures: Different in Structure but
the same in function
 These do not show evidence of evolutionary
relationships but, they do show natural selection

3. HOMOLOGY
Many organisms have similar bones though not
closely related. These are called Homologous
structures.
 Suggest a common ancestor, shows strong
evolutionary relationships
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Example: Birds, turtles, alligators, rats,
humans, and whales all have ―finger bones‖

Put picture of human, horse, cat, bat, bird,
whale here
4. VESTIGIAL STRUCTURES
any structure that is so reduced in function or
size that they are just vestiges or traces of the
original structure.
The structure may have been used in an
ancestor.
 The structure may be used in another animal
alive today.
 Examples: Appendix, small leg bones in
pythons, pelvic bones in whales
PICTURE OF VESTIGIAL STRUCTURES
4. EMBRYOLOGY

Of animals with backbones, the embryonic
stages look strikingly similar ; similar genes at
work
WHAT DOES THIS SUGGEST?
Similar genes early in development
 Suggests a common ancestor and evolutionary
relationships
 Groups of embryonic cells develop in the same
order and in similar patterns
 The same set of genes control this
development

5. BIOCHEMISTRY
The more closely related organisms are, the
more they will share in common biochemistry
(the chemistry of what makes up their bodies)
 They share similar DNA sequences and proteins
 Relatively new means of identifying
evolutionary relationships and has led to the reorganization of the history of several species.

Chapter
16 notes
CH. 16 IS ALL EVOLUTION THE SAME?
•
•
•
No, it does not happen in the same way across
all populations.
Natural selection on a single gene can just
change the allelic frequencies
With polygenic traits, it is more complicated.
EVOLUTION CAN OCCUR IN THREE WAYS
Directional selection
 Stabilizing Selection
 Disruptive Selection

POPULATIONS
If you think about the subtle varieties in a
population, you get a bell-shaped curve
 The most common variety is represented in the
middle and more extreme variations are on
either end of the curve. * (hair color)
 Evolution shifts the curve by changing the
percentage of each variation.

DIRECTIONAL SELECTION
In this case, Individuals on one end of the
curve are better adapted to their environment.
 EXAMPLE: Beak size (finches)
 The birds with the medium beak are the
majority.
 Small and large beaks are on the ends of the
curve. If a drought occurs and only the very
large seeds survive, only large-beaked birds will
be able to eat.

DIRECTIONAL SELECTION
STABILIZING SELECTION
When the average individual is best, the
population stabilizes-reduces the percentage of
organisms on the extremes
 Example: Birth weight in humans stays stable
because too small a weight is harmful for the
baby and too big a weight results in
complications at birth.

STABILIZING SELECTION
DISRUPTIVE SELECTION
This occurs when either extreme is better
adapted for survival than the average.
 EXAMPLE: most of a species of a butterfly are
brown. But, on either end of the population
curve, you see RED and BLUE
 Brightly colored butterflies resemble very
poisonous butterflies and thus, do not get
eaten

DISRUPTIVE SELECTION
SMALL POPULATIONS

The percentages of alleles change more
quickly- GENETIC DRIFT

If populations get separated and each new
population only has two of the four variations,
you have what is called a FOUNDER EFFECT

GENETIC drift and FOUNDER EFFECT
ARE POPULATIONS ALWAYS EVOLVING?
No!
 Populations will remain stable if the following
conditions are met:
 1) Random mating
 2) Large population
 3) No movement into or out of population
 4) No mutations
 5) No natural Selection
 THIS IS KNOWN AS THE HARDY- WEINBURG
PRINCIPLE

It is difficult for all
of the conditions to
be met.

dIt

There,
SO, HOW DO WE GET A NEW SPECIES
All of these changes over time can eventually
lead to a new species
 A species is defined as a group of organisms
that can interbreed and produce fertile
offspring
 This process is called SPECIATION
 Caused by 3 isolating mechanisms: Behavioral,
 Geographic, and temporal

BEHAVIORAL ISOLATION
Occurs when two populations are capable of
interbreeding but do not. (due to difference in
rituals/ behaviors)
 EX: Eastern and Western meadowlarks both
live in central US
 They do not mate because they use different
songs to attract their mates

GEOGRAPHIC ISOLATION
Geographic isolation occurs when 2
populations cannot reach each other to mate
due to a physical barrier.
 EX: earthquake in CA creates a huge crevasse
in the ground, isolating a population of lizards
 Since the two populations cannot mate, they
begin to have subtle changes over time that
make them different species

OTHER ANIMALS THAT OBEY GEOGRAPHIC
ISOLATION

Picture of mice?
TEMPORAL ISOLATION
Occurs when the species reproduce at different
times of the year.
 EX: 3 species of orchid all live in the same area
but, they never interbreed because they
release their pollen at different times of the
year.


Put picture of orchids and/ or other animals
that obey temporal speciation
PATTERNS OF EVOLUTION IN POPULATIONS
Adaptive radiation
 Convergent evolution
 Coevolution
 extinction

ADAPTIVE RADIATION
A single species evolves into more populations
by creating adaptations to different
environments or niches
 EX: Darwin’s finches – beak mutations led to
access of different food supplies

CONVERGENT EVOLUTION
Unrelated organisms resemble each other
since they have adapted to the same
environment.
 Ex: fish and dolphins both have fins
 Birds and dragonflies both have wings
 These are called analogous structures ( same
function but different structure)

COEVOLUTION
When two species evolve in response to one
another
 EX: Flowers and their pollinators must evolve
together. If the flower has a mutation that no
longer attracts the hummingbird, it will not
reproduce….and then, the hummingbird will
have to find a new food source.

EXTINCTION
When a species cannot adapt to its changing
environment
 Competition
 Climate change

HOW FAST CAN EVOLUTION OCCUR?

Gradualism- when evolution occurs slowly over
time ( most of what we have talked about)

Punctuated Equilibrium – when a major event
changes the distribution of a population…leads
to a quick burst of changes since mutations
spread quickly through small populations
CH. 16. A BRIEF HISTORY OF TIME
By looking at the fossil record, scientists have
learned that not all types of animals appeared
all at once.
 Using one of a variety of techniques, they can
figure out which ones are older.
 1) Relative: compare to others found in the
same layer
 2) Radioactive: uses isotopes and their
predictable rate of decay

A BRIEF HISTORY OF TIME
Earth’s atmosphere did not contain oxygen, so
microorganisms were the first to appear
(prokaryotic) ….in the water
Once oxygen appears, eukaryotic organisms
appear
Theory of Endosymbiosis – Eukaryotes arose
from prokaryotes that lived as a community
THEORY OF ENDOSYMBIOSIS

Ex. A prokaryote that does photosynthesis lives
inside another simple cell. Eventually their
DNA merges together ( one genome instead of
2)

A new, more complicated organism results
TIMELINE
1 Fish / simple plants
 2 Amphibians
 3 Reptiles and bush-like plants
 4 Birds / trees
 5 Simple Mammals
 6 Finally Primates

A BRIEF HISTORY OF TIME
Since all organisms have appeared
sequentially, it would seem logical to assume
that each gave rise to the other…..
 This is not quite the case.


Evolution argues that organisms share
ancestors not that one evolved into another.
TURNING INTO A TETRAPOD ( 4 LEGS)
So much to learn, so little time!
 Evolution is a whole course in college all by
itself!
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