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Evolution Review
Chapters 21, 22, & 23
Ch. 21
Genes within Populations
#2 5 Mechanisms of evolutionary
change
 1. Natural selection
 traits that improve survival
or reproduction will accumulate
in the population
 adaptive change
 2. Genetic drift
 frequency of traits can change
in a population due to
random chance events
 random change
 More pronounced in small populations
#2 and #9: Genetic Drift
 Chance events changing frequency of traits in a
population
 not adaptation to environmental conditions
 not selection
 founder effect
 small group splinters off & starts a new colony
 it’s random who joins the group
 bottleneck
 a disaster reduces population to
small number & then population
recovers & expands again but
from a limited gene pool
 who survives disaster may be random
Founder effect
 When a new population is started
by only a small group of individuals
 just by chance some rare alleles may
be at high frequency;
others may be missing
 skew the gene pool of
new population
 human populations that
started from small group
of colonists
 example:
colonization of New World
Don’t fence
me in!
albino deer Seneca Army Depot
Out of Africa
Likely migration paths of humans out of Africa
Many patterns of human traits reflect this migration
Bottleneck effect
 When large population is drastically reduced by a
disaster
 famine, natural disaster, loss of habitat…
 loss of variation by chance event
 alleles lost from gene pool
 not due to fitness
 narrows the gene pool
Cheetahs
 All cheetahs share a small number of alleles
 less than 1% diversity
 as if all cheetahs are
identical twins
 2 bottlenecks
 10,000 years ago
 Ice Age
 last 100 years
 poaching & loss of habitat
Peregrine Falcon
Conservation issues
 Bottlenecking is an important concept in
conservation biology of endangered
species
 loss of alleles from gene pool
 reduces variation
 reduces adaptability
Breeding programs must
consciously outcross
Golden Lion
Tamarin
5 Agents of evolutionary
change
Mutation
Gene Flow
Genetic Drift
Non-random mating
Selection
#3: Variation & natural
selection
 Variation is the raw material for natural selection
 there have to be differences within population
 some individuals must be more fit than others
Ch. 22
Evidence for Evolution
LaMarck (1744-1829)
 Organisms adapted to
their environments by
acquiring traits
 change in their life time
 Disuse
organisms lost parts because they did not use them — like
the missing eyes & digestive system of the tapeworm
 Perfection with Use & Need
the constant use of an organ leads that organ to increase
in size — like the muscles of a blacksmith or the large
ears of a night-flying bat
 transmit acquired characteristics to next generation
Then along comes Darwin…
Charles Darwin
 1809-1882
 British naturalist
 Proposed the idea of
Galapagos
evolution by natural
Islands
selection
 Collected clear
evidence to support
his ideas
1831-1836
22 years old!
But Darwin found… a lot of
finches
Darwin was amazed to
find out:
All 14 species of birds
were finches…
But there is only one
Large Ground
species of finch on theFinch?
Finch
mainland!
Small Ground
Sparrow?
Finch
How did
one species
of finches become
so many different
species now?
Warbler Finch
Woodpecker?
Veg. Tree Finch
Warbler?
Correlation of species to food source
Seed
eaters
Flower
eaters
Insect
eaters
Rapid speciation:
new species filling new niche
because they inherited
successful adaptations.
Adaptive radiation
Darwin’s finches
 Differences in beaks
allowed some finches to…
 successfully compete
 successfully feed
 successfully reproduce
 pass successful traits
onto their offspring
More observations…
Correlation of species
to food source
Whoa,
Turtles, too!
Many islands also show
distinct local variations in
tortoise morphology…
…perhaps these are
the first steps in the
splitting of one species
into several?
More observations…
Glyptodont fossils
Sloth fossils
Modern sloth
Modern armadillos
Why should extinct
species & living species
be found on the
same continent?
Essence of Darwin’s ideas
 Evolution by Means of Natural Selection
 variation exists in populations
 over-production of offspring
 more offspring than the environment can support
 competition
 for food, mates, nesting sites, escape predators
 differential survival
 successful traits = adaptations
 differential reproduction
 adaptations become more
common in population
LaMarckian vs. Darwinian
view
 LaMarck
 in reaching higher
vegetation giraffes
stretch their necks & transmits the
acquired longer neck to offspring
 Darwin
 giraffes born with longer necks

survive better & leave more
offspring who inherit their long
necks
What are the 4 lines of evidence that
support Darwin’s ideas?…
Human Macaque Dog Bird
8
32 45
Frog
Lamprey
67
125
0 10 20 30 40 50 60 70 80 90 100 110 120
1. What are the lines of evidence that support Darwin’s ideas?
Fossil record
550
500
Body size (kg)
450
Equus
400
350
300
250
Merychippus
200
150
Mesohippus
Hyracotherium
100
50
Nannippus
60 55 50 45 40 35 30 25 20 15 10
Millions of years ago
5 0
2. What are the lines of evidence that support Darwin’s ideas?
Terminal
bud
Lateral
buds
Cabbage
Brussels
sprouts
Artificial selection
Leaves
Flower cluster
Kale
Cauliflower
Broccoli
Stem
Flower
and
stems
Wild mustard
Kohlrabi
3. What are the lines of evidence that support Darwin’s ideas?
Anatomical evidence
Homologous structures
 Similar structure
 Similar development
 Different functions
 Evidence of close evolutionary
relationship
 recent common ancestor
Analogous structures
Convergent
Don’t
be fooled
by
their looks!
evolution
Those
fins
& tails
Does this
mean
&
sleek
are
they
havebodies
a
recent common
ancestor?
analogous
structures!
Solving a similar problem with a similar solution
Vestigial organs
These are
Why would whales
remnants of
have pelvis & leg bones
structures that were
if they were always
functional in
sea creatures?
ancestral species
4. What are the lines of evidence that support Darwin’s ideas?
Molecular record
 Comparing DNA & protein structure
 universal genetic code!
 DNA & RNA
 compare common genes
 cytochrome C (respiration)
 hemoglobin (gas exchange)
Human/kangaroo
Closely related species have sequences that
are more similar than distantly related
species
 DNA & proteins are a molecular
record of evolutionary relationships
Nucleotide substitutions
100
Dog/
cow
75
Human/
cow
Rabbit/
rodent
50 Horse/
donkey
Llama/
cow
Horse/cow
Sheep/
goat
25
Human/rodent
Pig/
cow
Goat/cow
0
0
25
50
75
100
Millions of years ago
125
Human
Macaque
Dog Bird
Frog
Lamprey
The sequence in
DNA
& proteins
Why compare
is
a molecular
DNA
& proteins
record
of evolutionary
across species?
relationships.
Comparative hemoglobin structure
8
32
45
67
125
Why compare
these genes?
0
10 20 30 40 50 60 70 80 90 100 110 120
Number of amino acid differences between  compare common genes
hemoglobin (146 aa) of vertebrate species and that
of humans C (respiration)
 cytochrome
 hemoglobin (gas exchange)
Convergent evolution
marsupial
mammals
These animals
look very similar but does
that mean they have a
recent common ancestor?
What is this
evidence of?
placental
mammals
Parallel/convergent evolution
Niche
Burrower
Placental Mammals
Mole
Convergent evolution
of analogous
Marsupial mole
burrowing characteristics
Australian Marsupials
Anteater
Anteater
Nocturnal
insectivore
Mouse
Climber
Numbat
Marsupial mouse
Spotted cuscus
Lemur
Glider
Stalking
predator
Chasing
predator
Sugar glider
Flying
squirrel
Ocelot
Tasmanian cat
Wolf
Tasmanian “wolf”
Coevolution
 Two or more species reciprocally
affect each other’s evolution
 predator-prey
 disease & host
 competitive species
 mutualism
 pollinators & flowers
#7. Types of Natural Selection
 Selection acts on any trait that affects survival or
reproduction
 predation selection
 physiological selection
 sexual selection
#8. Effects of Selection
 Changes in the average trait of a population
DIRECTIONAL
SELECTION
STABILIZING
SELECTION
DISRUPTIVE
SELECTION
speciation?
giraffe neck
horse size
human birth weight
rock pocket mice