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EVOLUTION
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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
1. Sexual Reproduction ( Random Shuffling of
alleles)
2. Mutations
3. 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. Hood
Island tortoise – long neck and curved shell
that is open and allows it reach sparse
vegetation

HOOD ISLAND

Isabela Island(below)
Pinta
Island
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

EVOLUTION BY NATURAL SELECTION
Definition: process by which
individuals that are better
suited to their environment
survive and reproduce most
successfully.
THE PEPPERED
MOTH
3/8
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.

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.
 Examples are:
 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


There are many more adaptations besides
camouflage and mimicry. (Behaviors, sounds,
etc.)
EVIDENCE OF EVOLUTION
1 Fossils
 2 Geographical distribution
 3 Homology
 4. Vestigial Structures
 5 Embryology
 6 Biochemistry (the chemistry of living
organisms)

FOSSILS
1) Fossils:
 Remnants of 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

2) GEOGRAPHIC DISTRIBUTION
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


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
 Tonsils actually DO HAVE A FUNCTION even though
they can be removed.
PICTURE OF VESTIGIAL STRUCTURES
5. EMBRYOLOGY

Of animals with backbones, the embryonic
stages look strikingly similar ; similar genes at
work
WHAT DOES THIS SUGGEST?
Suggests a common ancestor and evolutionary
relationships
 Groups of embryonic cells develop in the same
order and in similar patterns

6. BIOCHEMISTRY
The more closely related organisms are, the
more they will share in common biochemistry
(the chemistry of what makes up their bodies)
 similar DNA sequences and proteins
 Relatively new means of identifying
evolutionary relationships
 has led to the re-organization of the history of
several species * can tell when species
diverged from one another

CHAPTER 17 NOTES: EVOLUTION AND
POPULATIONS
CH. 17 IS ALL EVOLUTION THE SAME?
•
No, it does not happen in the same way across
all populations.

Genetic variation in organisms is studied at the
level of a population not the individual.

A population is a group of individuals of the
same species that live in the same area.
POPULATIONS

Members of a population of species interbreed,
therefore they share a common group of genes
called a gene pool.

Gene Pool: all of the genes that are present in
a population. This includes all the different
alleles.

The relative (allelic) frequency of an allele is the
number of times that the allele occurs in a gene
pool compared to the number of times other
alleles for the same gene occur.
Q: How do new alleles arise?
 Through random mutations.
 Gene shuffling – during meiosis
 Crossing over
 Sexual Reproduction
RECALL FROM SLIDE #2 *

evolution : any change in the relative frequency
of alleles in a population.

if the frequency of the allele changes, then the
population is evolving.
RECALL FROM GENETICS

Inheritable variation can be expressed by either
single-gene traits or by polygenic traits.

The number of phenotypes produced for a
given trait depends on how many genes control
the trait.
EVOLUTION CAN OCCUR IN THREE WAYS

Directional selection

Stabilizing Selection

Disruptive Selection
POPULATIONS
Most phenotypes in generations form a bell –
shaped curve
 The most common variety is represented in the
middle of the curve 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
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

The average beak size increases since more of
the larger beaked finches could survive and
reproduce.
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 – random change in
allelic frequency
If populations get separated and each new
population only has two of the four variations,
you have what is called a FOUNDER EFFECT
 Def: Change in allele frequencies as a result of
migration of a small subgroup


FOUNDER EFFECT
BOTTLENECK EFFECT

Change in allelic frequency after a dramatic
reduction in the size of a population.

Example: a natural disaster such as a tornado or
hurricane wipes out a population but a few
individuals remain. Those individuals may have
very different alleles from the original population.
Therefore, the population that grows will be
different from the original population.
ARE POPULATIONS ALWAYS EVOLVING?
No, but there are 5 conditions which must be
met for a population not to be evolving.
 Requirements to maintain genetic equilbrium:
 1) Random mating
In nature, random mating rarely occurs.
 Example: Lions select their mates based on
size or strength.

2) Large population
 3) No movement into (immigration) or out of
population (emmigration)
 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? 17.3

All of these changes over time can eventually
lead to a new species

This process is called SPECIATION
3 TYPES OF SPECIATION

Caused by 3 isolating mechanisms:
Behavioral
 Geographic
 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
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

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.

ORCHIDS
CH. 19 HISTORY OF LIFE ON EARTH
And, should I
become a
paleontologist
rather than a
dentist?
CH. 19
Geologic evidence shows
that Earth is about 4.6
billion years old.
By the fossil record, scientists have learned
that not all types of animals appeared all at
once.
Fact: more than 99 percent of all species that
have ever lived on Earth have become extinct.
Earliest life forms appeared in rocks more than
3.5 billion years old.
 Paleontologists – scientists who study fossils

FOSSILS… WHAT DO YOU LOOK AT?



1.Anatomical similarities and differences
between the fossil organism and organisms
living today.
2. The fossil’s age.
3. What the environment may have been like
when the organism was alive. This may tell you
what the organism ate and how it lived.
DATING METHODS

1) Relative: The age of the fossil is determined
by comparing its placement in the sedimentary
rock with that of fossils in other layers
 Index fossils are used
WHAT ARE INDEX FOSSILS?
Fossils of a species that are easily recognized.
Existed for only a short period of time so it will
only be found in a few layers of rock.
Had a wide geographic distribution. * meaning
that it can be found in many locations around
the world.
RADIOACTIVE DATING
2) Radioactive: calculate absolute ages of the
fossil based on the amount of remaining
radioactive isotope it contains.
 Different radioactive isotopes have different
half-lives (rates of decay).
 EX: Carbon-14: decays into nitrogen-14 every
5739 years which is called the half-life.
 EX: Potassium-40: decays into argon-40 every
1.26 billion years.

HOW DOES RADIOACTIVE DATING WORK
EXACTLY? (CARBON DATING)





All plants and animals incorporate carbon into their
tissues during their lives for growth and energy.
When an organism dies, it stops incorporating carbon
(all forms of carbon, including C14) into its structure.
The amount of radioactive carbon (C14) that had been
in the organism when it was alive begins to decrease at
death as it loses nuclear particles through radioactive
decay.
C14 is only good for dating fossils younger than 60, 000
years old
the "clock" starts ticking when death occurs.
SEQUENCE OF EVENTS (PER THE GEOLOGIC
RECORD)
Early bacteria-like cells/ prokaryotes
 First Eukaryotes
 Fish and simple plants
 Amphibians
 Reptiles and bush-like plants
 Birds and trees
 Simple mammals (rodents)
 Primates

WHAT WAS THE EARTH LIKE BEFORE
PRECAMBRIAN 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 –
Eukaryotic cells arose from living communities
formed by prokaryotic cells.
THEORY OF ENDOSYMBIOSIS
Mitochondria and chloroplasts contain their
own DNA
 Mitochondria and chloroplasts have ribosomes
that make their own proteins.
 Like bacteria, mitochondria and chloroplasts
have many of the features of free-living bacteria
such as being able to grow and reproduce
independently of the cell.

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!

RATES OF EVOLUTION
Evidence shows that evolution has proceeded
at different rates for different organisms at
different times.
 1.) Gradualism- Gradual change/ slow and
steady change
 2.) Punctuated Equilibrium- equilibrium
interrupted by brief periods of rapid change.
 Rapid can mean a few thousand years in terms
of geologic time.

Rapid evolution occurs most frequently in small
populations.
EX: - founder effect, bottleneck effect

PATTERNS OF EVOLUTION IN POPULATIONS

Adaptive radiation

Convergent evolution

Coevolution

extinction
ADAPTIVE RADIATION/ DIVERGENT EVOLUTION

A single species evolves into more populations
by creating adaptations to different
environments or niches
EX: Darwin’s finches –
 Hawaiian Fruit flies 
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
 RECALL: 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

So much to learn, so little time!
 Evolution is a whole course in college all by
itself!
