The Theory of
Evolution and
Natural Selection
Evolution is neither more nor less than the result of respecting
the reality and consistency of the physical world over time.Renowned Cell Biologist Kenneth Miller
1/20/2015 Warm-Up
• Answer the following questions in your own words:
• 1. What is the difference between a scientific theory and
a belief?
• 2. Define evolution in your own words
• 3. Do you feel that there is an 'either /or' choice
between religious beliefs and evolutionary theory - ie.
that you must reject the idea of evolution because of
your religious beliefs, or that you can't believe in God if
you accept the evidence for evolution? Is it possible to
have both a belief in God and an acceptance of the
evidence supporting evolution?
But It’s Only a Theory,
Right?
• In science, theories are statements or models
that have been tested and confirmed many
times.
• In science, the term "Theory" does not express
doubt.
• They explain a wide variety of data and observations
• They can be used to make predictions
• They are not absolute, can be changed as new
evidence is found
Observations help Explain
• Why do so many different animals
have the same structures, the arm
bones in a human are the same
bones as a flipper in a whale?
• Why is the sequence of DNA very similar in some
groups of organisms but not in others?
• Why do the embryos of animals look very similar
at an early stage?
• As the 19th century dawned, it was generally
believed that species had remained
unchanged since their creation
• However, a few doubts about the
permanence of species were beginning to
arise
Darwin’s Research
• As a boy and into adulthood, Charles Darwin
had a consuming interest in nature
• Darwin’s father sent him to medical school,
but he found medicine to be boring and quit.
• He enrolled at Cambridge University to be
become part of the clergy of the church.
o Most scientists at this time were also clergymen.
• After graduation, he went on a voyage
around the world on a ship called the HMS
Beagle.
The Voyage of the Beagle
• During his travels on the Beagle, Darwin was able to
observe adaptations of plants and animals from
many diverse environments.
o Rainforests of Brazil
o Grasslands of Argentina
o Mountains of Peru
• One of the most important visits he made was to the
Galápagos Islands west of South America
LE 22-5
England
EUROPE
NORTH
AMERICA
PACIFIC
OCEAN
ATLANTIC
OCEAN
AFRICA
Galápagos
Islands
HMS Beagle in port
Equator
SOUTH
AMERICA
Darwin in 1840,
after his return
AUSTRALIA
Cape of
Good Hope
Tasmania
Cape Horn
Tierra del Fuego
New
Zealand
The Galapagos Islands
• Darwin found animals on these islands that weren’t
found anywhere else in the entire world.
• He theorized that the animals had migrated from
South America and then began developing specific
adaptations to their new environment.
The Galapagos Islands
• Darwin also noted that the animals on the
Galapagos islands were amazingly unafraid of
humans.
• After watching a lizard that was partly buried in the
sand, he wrote this:
“I then walked up and pulled it by the
tail; at this it was greatly astonished,
and soon shuffled up to see what was
the matter; and then stared me in the
face, as much as to say, “What made
you pull my tail?”
Darwin’s Focus on
Adaptation
• Darwin noted many adaptations, or characteristics
that enhanced the organisms chances of survival.
• He began to form a theory that as organisms
gradually accumulated new adaptations, they would
form a new species.
o One of the best examples of this theory is the different species
of finches on the islands.
o The birds were all very similar except for their beaks.
LE 22-6
The long, sharp beak
of the cactus ground
finch (Geospiza
scandens) helps it tear
and eat cactus flowers
and pulp.
The large ground finch
(Geospiza magnirostris)
has a large beak adapted
for cracking seeds that fall
from plants to the ground.
The green warbler finch (Certhidea
olivacea) used its narrow, pointed beak
to grasp insects.
• In 1844, Darwin wrote an essay on the
origin of species and natural selection
but did not introduce his theory publicly,
anticipating an uproar.
o His theory suggested that new
species developed over time
naturally, not directly from God.
• In June 1858, Darwin received a
manuscript from Alfred Russell Wallace,
who had developed a theory of natural
selection similar to Darwin’s.
• Darwin quickly finished his book, entitled
The Origin of Species and published it
the next year.
The Origin of Species
• The ideas of Origin of Species can be
summarized with these two main points:
o Evolution explains life’s unity and diversity.
o Natural selection is a cause of evolution.
Descent with Modification
• Darwin did not call his theory “evolution”.
• He used the phrase descent with modification.
o This means that all organisms are related.
o All species came from a common ancestor.
• In the Darwinian view, the history of life is like a tree
with branches representing each new species.
o Each new species is simply a “modified” version of its
ancestor.
LE 22-7
Sirenia
Hyracoidea (Manatees
(Hyraxes) and relatives)
0
10,000
2
5.5
24
34
Elephas Loxodonta Loxodonta
cyclotis
maximus africana
(Africa)
(Africa)
(Asia)
Natural Selection and
Adaptation
• Charles Darwin’s theory can be broken down
into five different observations.
o
Observation #1: For any species, population sizes would
increase exponentially if all individuals that are born
reproduced successfully.
• Observation #2: Populations tend to be stable in size,
except for seasonal fluctuations
• Observation #3: Resources are limited
• Observation #4: Members of a population vary in their
characteristics; no two individuals are exactly alike
• Observation #5: Much of this variation is heritable
Warm-Up 1/21/2015
• (Answer the question, don’t worry about writing it)
Charles Darwin, in his theory on the origin of species,
proposed that characteristics that enhanced the
organisms chances of survival were vital to success
of the organism. What are these characteristics
known as?
• Adaptations
• Conclusion #1: More
individuals are produced
than the environment can
support;
o Frogs lay thousands of eggs at a
time, but only about 1% survive to
adulthood.
Play the Roll for Survival Game!
http://www.torontozoo.com/adoptapond/3games.asp
• Inference #2: Survival depends in part on
inherited traits.
o Individuals with traits that give them an advantage
are more likely to reproduce and have offspring.
• Inference #3: Individuals that reproduce the most will
pass favorable characteristics to their offspring.
o Over generations, these characteristics will accumulate.
Summary of Natural
Selection
• Natural selection is differential success in reproduction
from interaction between individuals that vary in
heritable traits and their environment
• Natural selection produces an increase over time in
adaptation of organisms to their environment
• If an environment changes over time, natural
selection may result in adaptation to these new
conditions
Key Points to Consider
• 1. Variation exists among individuals in a species.
2. Individuals will compete for resources (food, mates,
and space)
3. Competition would lead to the death of some
individuals while others would survive
4. Individuals that had advantageous variations are more
likely to survive and reproduce.
• 5. Evolution is change over time
This process came to be
known as Natural Selection
The favorable variations are
called Adaptations
1/22/2015 Warm-Up
Analyze and evaluate this graph in your own words
1/23/2015 Warm-Up
• During our Avis Origamis exploration, we saw how
small changes, or adaptations, can make an
impact on future generations. Assume that on the
Avis Origamis island, birds that fly long distances are
no longer selected for. How might the bird’s species
change over time?
• Once you write your answer, bring your notebook to
me so that I can check your notebook.
Finish Your Activity
• Raise your hand if you need assistance
• Answer the concept development questions
• Turn your activity in today
Warm-up 1/26/2015
• In a population of 1,000 individuals, the
frequency of fur that is red to fur that is
white is 0.5/0.5
o Answer: How many individuals of each color are present in
the population?
o Answer: What would happen to gene frequency if a
randomized subset of the population broke off that was
not representative of the original population?
1:12
1:13
1:14
1:15
1:16
1:17
1:18
1:19
1:20
1:21
1:22
1:23
1:24
1:25
1:26
1:27
1:28
1:29
1:30
1:31
1:32
1:33
1:34
1:35
1:36
1:37
1:38
1:39
1:40
1:41
1:42
1:43
1:44
1:45
1:46
1:47
1:48
1:49
1:50
1:51
1:52
1:53
1:54
1:55
1:56
1:57
1:58
1:59
0:12
0:13
0:14
0:15
0:16
0:17
0:18
0:19
0:20
0:21
0:22
0:23
0:24
0:25
0:26
0:27
0:28
0:29
0:30
0:31
0:32
0:33
0:34
0:35
0:36
0:37
0:38
0:39
0:40
0:41
0:42
0:43
0:44
0:45
0:46
0:47
0:48
0:49
0:50
0:51
0:52
0:53
0:54
0:55
0:56
0:57
0:58
0:59
1:00
1:01
1:02
1:03
1:04
1:05
1:06
1:07
1:08
1:09
1:10
0:01
0:02
0:03
0:04
0:05
0:06
0:07
0:08
0:09
0:10
2:00
1:11
0:11
End
Mechanisms of Evolution
• Natural Selection
• Genetic Drift
o Population Bottlenecks
o Founder Effect
• Gene Flow
o Immigration
o Emigration
• Mutations
• Mimicry
Genetic Drift
• Changes in gene pool of populations due to random
chance
Genetic Drift
Genetic Drift
Image Credit: UC Museum of Paleontology's Understanding Evolution www.evolution.berkeley.edu
Genetic Drift
• Genetic drift has a bigger effect on small populations.
Bottleneck Effect
• Changes in gene pool of populations due to some event
 drastically reduces population
Bottleneck Effect
• Survival is random
• Whether an organism survives does not depend on any
characteristic (allele)
Example of Bottleneck Effect
• Population of plants on
a mountain side
• An avalanche wipes
out all but a patch of
plants behind the
shelter of a large
outcrop.
Example of Bottleneck Effect
• Plants behind the outcrop survived only because they
were out of the path of the avalanche.
• There was nothing about the plants’ genes that
influenced survival.
• Surviving population has an allele frequency different
from the original population.
Bottleneck Effect
Bottleneck Effect: Cheetahs
• 10,000 years ago,
cheetah populations
worldwide crashed
• Due to climate change
•
Photo Credit: Courtesy of Smithsonian National
Zoo @ nationalzoo.si.edu
Cheetahs
• Only cheetahs in
Africa & Eurasia
survived
• Location, not
genes  Survival
•
Photo Credit: Kevin Walsh, 2006,
Wikimedia Commons
Cheetahs
• Cheetahs today: Genetically, essentially identical
•
Photo Credit: Lukas Kaffer, 2007, courtesy of Wikimedia Commons
Bottleneck Effect:
Northern Elephant Seals
• Once numerous in
the northern Pacific.
• 1800s: Hunted
extensively for
blubber
•
Photo Credit: Michael Baird of bairdphotos.com,
courtesy of Wikimedia Commons
Northern Elephant Seals
• Only 100-1000
animals in a
Mexican colony
survived
•
Photo Credit: Michael Baird of bairdphotos.com,
courtesy of Wikimedia Commons
Northern Elephant Seals
• Today:
>100,000
individuals
• Very little
genetic
diversity
•
Photo Credit: Mila Zinkova, 2008,
courtesy of Wikimedia Commons
Founder Effect
• New population established by very small number of
individuals (“founders”)
• By chance, founder group has a different allele mix than
original population
Example of Founder Effect
• In 1744, 200
German
immigrants
founded the Old
Order Amish of
Pennsylvania
•
Photo credit: : Matthew Trump, 2004,
Wikimedia Commons
Old Order Amish
• One couple
brought allele
polydactyly  Six
fingers and toes
•
Photo credit: G. Baujat and M
LeMerrer, 2007, Wikimedia
Commons
Old Order Amish
• Inbreeding has 
frequency of polydactyly
• Click on this link:
http://www.pbs.org/wgbh/evolution/library/
06/3/l_063_03.html
•
Photo credit: gadjoboy, 2006, Wikimedia
Commons
Warm-Up 1/27/2015
• Evaluate why genetic
drift impacts a small
population in a much
bigger fashion than it
does a large
population
3 minutes
• the effects of genetic
drift on large
populations are minor
compared to the entire
gene pool . Genetic
drift working in small
populations can quickly
result in big changes
because the gene pool
is much smaller and
changes are more
readily identifiable
Characteristics Key
• Yellow-Camouflage
• Black-Precise Vision
• Orange-Accurate sense of
smell
• Pink-Strong claws and
forearms
• Dark Blue-Healthy Jaw
formation
• Green-Agility
• Purple-Acute Hearing
• Red-Healthy reproduction
• White-Immunity to canine
distemper
• For each environmental
condition you select, is
your population adapted
to survive? (5 answers)
• Overall, will your
population survive the 5
environmental changes
• Por favor mantengase
alejad de las puertas
Warm-Up 1-28-2015
• Today there will be no warm-up since
we are having a quiz. Once your quiz
starts, you have 20 minutes to
complete the quiz so that we can then
move on to finish our mechanisms of
evolution. We have 21 slides remaining
to cover!
Missing Vocabulary
• I graded vocabulary last night. This means that it is
now late if it has not been turned in. If I don’t have
your vocab, it’s been recorded as “M” in the
gradebook. Vocab was assigned 1/20/2015 and
had a due date of 1/26/2015.
• 2nd Period: 9/24 are missing the assignment
• Turn it in for -15 pts today.
• Turn it in tomorrow for another -15 pts
Gene Flow
• Movement of alleles between populations
• Immigration: movement of alleles into a
population
• Emigration: movement of alleles out of
population
Example of Gene Flow
• Transfer of pollen from
one population of
sunflowers into another
population of
sunflowers
•
Photo Credit: Sunflower Pollen, Courtesy of
Wikimedia Commons
Example of Gene Flow
• Male juvenile Belding’s
ground squirrels
emigrate from their
birthing population to
new populations.
• 40-70% emigrate as
juveniles. Remaining
males leave by the end
of their first year.
•
Photo Credit: Courtesy of Yathin at FlickR,
http://www.flickr.com/photos/yathin/807378578/i
n/set-72157600812861150/
Mutations
• Mutations can add
new alleles to a
population
• Mutations occur
during the cell
cycle during
interphase, when
DNA is copied.
Can also be
environmental!
Mimicry
• The similarity of one species to another which
protects one or both species
o Can be appearance, behavior, sound, scent, or location
• Mimicry is related to camouflage
• Occurs when a group of organisms, the mimics,
evolve to share common perceived characteristics
with another group---the models
Which is deadly and
which is friendly?
Deadly
Friendly
Populations are the units of
evolution
Figure 13.6
Five agents of microevolution
1. Mutation changes alleles
2. Genetic drift = random changes in allele
frequency
Bottleneck
Founder effect
3.
Gene flow can change a gene pool due to the
movement of genes into or out of a population
ex. Migration
4. Nonrandom mating within a population
5. Natural selection leads to differential
reproductive success
What are sources of
genetic variation?
• Mutation can create new alleles, new genes.
• Sex - Recombination of genes in sexual reproduction
There are three general outcomes of natural
Frequency of
individuals
selection
Original
population
Phenotypes (fur color)
Original
population
Evolved
population
Stabilizing selection
Directional selection
Diversifying selection
Figure 13.19
Types of Natural Selection
• Stabilizing: occurs when natural selection favors the
intermediate states of continuous variation. Over time,
the intermediate states become more common and
each extreme variation will become less common or lost.
• Directional: occurs when natural selection favors one
extreme of continuous variation. Over time, the favored
extreme will become more common and the other
extreme will be less common or lost.
• Diversifying: describes changes in population genetics in
which extreme values for a trait are favored over
intermediate values. In this case, the variance of the trait
increases and the population is divided into two distinct
groups
80
beak depth
1976
Number of individuals
60
40
Average
beak depth,
1976
20
Average
beak depth,
1978
1978
0
5
6
7
8
9
10
11
12
13
Beak depth (mm)
Shift of average beak
depth during drought
14
What is a species?
• appearance alone does not always define a species
– Example: eastern and western meadowlarks
Figure 14.1A
What is a species?
• Naturally interbreeding populations
- potentially interbreeding
- reproductively isolated from other species
What about asexually reproducing organisms?
Extinct species?
Shy species?
When
does
speciation
MECHANISMS OF SPECIATION
occur?
• When geographically isolated, species evolution may
occur
o gene pool then changes to cause reproductive isolation
= allopatric speciation
Figure 14.3
Reproductive barriers
between species
•
•
•
•
•
•
Habitat - different locations
Timing - mating, flowering
Behavioral - mating rituals, no attraction
Mechanical - structural differences
Gametic - fail to unite
Hybrid weak or infertile
• Courtship ritual in blue-footed boobies is an example
of behavioral isolation
• Many plant species have
flower structures that
are adapted to specific
pollinators
– mechanical isolation
Figure 14.2A, B
• Hybrid sterility is one type of postzygotic barrier
– A horse and a
donkey may
produce a hybrid
offspring, a mule
– Mules are sterile
Figure 14.2C
•
•
•
•
Sympatric speciation
No geographical isolation
Mutation creates reproductive isolation
Polyploidization
Hybridization
Cactus
ground finch
Medium
ground finch
Large
ground finch
Small
Large cactus
ground finch ground finch
Small
tree finch
Vegetarian
finch
Medium
tree finch
Large
tree finch
Woodpecker
finch
Mangrove
finch
Green
Gray
warbler finch warbler finch
Sharp-beaked
ground finch
Seed
eaters
Cactus flower
eaters
Ground finches
Bud
eaters
Insect
eaters
Tree finches
Warbler finches
Common ancestor from
South America mainland
When does speciation occur?
When does speciation
occur?
• Specialists - Galapagos finches
• Generalists - horseshoe crabs, cockroaches
• New environments
- ecological niche
Speciation - how much
change is needed?
• Gradual vs. jerky
• Evidence:
o Fossil record
o Genetic differences between species
o Homeotic genes