AP Biology – Chapter 22
Evolution –
Descent with
Modification
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Campbell Chapters 22-24
Science happens within a culture
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Evolution
  Descent with modification
  Change in genetic composition of a
population from generation to
generation
  Pattern and process
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AP Biology – Chapter 22
The Pattern of Evolution
  Revealed by data from a range of
scientific disciplines
  Ex: biology, geology, physics, chemistry
  Data are facts – observations of the natural world
The Process of Evolution
  Consist of the mechanisms that
produce the observed pattern of
change
  Natural causes of the natural phenomena we
observe
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Before Darwin…..
  Plato – idealism or essentialism
Viewed as 2 coexisting worlds:
  Ideal, eternal, real world
  Illusionary, imperfect world perceived by our
senses (the world we live in)
  Allows for NO evolution

  Aristotle (384-322 BC) – viewed species as fixed
Scala Naturae – “Scale of Nature” - Classification of
Species
  Thought species could be arranged on a scale of
increasing complexity  simple to complex
  Allows for no evolution since all organisms are fixed
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in their position

Before Darwin…..
  Linnaeus (1707-1778) – founder of
taxonomy
classified life’s diversity “for the greater glory of
God.”
  Developed a binomial nomenclature (Homo
sapiens)
  Grouped similar species together into general
categories (species, genus, family, etc.) figure
1.14
  Allows for NO evolution since clustering of species
did NOT imply evolutionary relationships

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AP Biology – Chapter 22
Before Darwin…..
  Cuvier (1769-1832)
Studied fossils (paleontology) – remains
or traces of organisms from the past
  Noticed fossil differences in each layer
(strata) of rock as he dug deeper
  Catastrophism – his view of the earth –
changes in species found in each strata
were due to major catastrophes or
extinctions
  Allows for NO evolution

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Before Darwin….
  Hutton and Lyell

Uniformitatianism – geological processes are so
uniform and gradual that their rates and effects
must balance out over time
  Mechanisms of change are constant over time
  Proposed that the same geological processes operating
today as in the past, and at the same rate

Their ideas strongly influenced Darwin’s thinking
  Darwin agreed that if geological change results from
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slow, continuous actions rather than sudden events, then
the earth must be older than originally thought
  Idea of gradual change – slow accumulation of small
changes could ultimately produce profound changes
  Age of the earth was important for Darwin – unless Earth
was very old – he could not envision how their would be
time for evolution to occur
Before Darwin…..
  Lamark (1744-1829)

Developed a comprehensive theory as to
HOW life evolved over time
1.  Use and Disuse – parts of the body that are
used become larger/stronger and those that
are not used will deteriorate
2.  Inheritance of acquired characteristics –
modifications that an organism acquires
during its lifetime can be passed on to its
offspring
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AP Biology – Chapter 22
Then along comes Darwin…
1831-1836
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22 years old!
Charles Darwin (1809-1882)
  Galapagos Islands (540 miles west of
South America)
Fascinated by the unusual organisms he found
there
  Finches and fauna unique to Island but resemble
mainland
  Geographical distribution of species may lead to
development of new species as each population
adapts to local conditions

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Charles Darwin (1809-1882)
  Adaptations – characteristics of organisms that
enhance their survival and reproduction in specific
environments
  The finches’ various beaks and behaviors are
adapted to the specific foods available on their
home islands
  Natural Selection

Darwin’s explanation of how
adaptations arise centered on natural
selection
  A process in which individuals with certain
inherited traits leave more offspring than
individuals with other traits
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AP Biology – Chapter 22
Then along comes Darwin…
& those dang finches!
Descendant
species
Warbler finch
Cactus finch
Ancestral
Woodpecker finch
species
Sharp-beaked finch
ef
Cactus
eater
Insect eaters
Seed eaters
Vegetarian
tree
finch AP
Biology
es
ch
fin
Tr
e
Small ground
finch
r
Warble
finch
nd
ou
Gr
Large
insectivorous
tree finch
in
ch
es
Small insectivorous
tree finch
Medium
ground finch
Large
ground finch
Bud eater
Correlation of species to food source
Rapid speciation:
new species filling niches,
because they inherited
successful adaptations.
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radiation
Adaptive
Beak variation in Galapagos finches
(a)
Cactus eater. The long,
sharp beak of the cactus
ground finch (Geospiza
scandens) helps it tear
and eat cactus flowers
and pulp.
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(c)
Seed eater. The large ground
finch (Geospiza magnirostris)
has a large beak adapted for
cracking seeds that fall from
plants to the ground.
(b) Insect eater. The green warbler
finch (Certhidea olivacea) uses its
narrow, pointed beak to grasp insects.
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AP Biology – Chapter 22
“The Origin of Species”
  Darwin developed 2 main concepts:
1.  Descent with modification – all organisms related
through descent from unknown prototype that lived
in the past


Diverse adaptations accumulated as descendants from
this common ancestor moved into various habitats
over millions of years
Adaptation – inherited variation that increases an
organisms likelihood of surviving to reproduce
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“The Origin of Species”
  Darwin developed 2 main concepts:
2.  Natural Selection – proposed mechanism to explain
the observable patterns of evolution

Darwin described 4 observations of nature from which
he drew 2 inferences:
Observation 1 – Members of a population often vary greatly in
their traits (much of this variation is inherited)
Observation 2 – Traits are inherited from parents to offspring
Observation 3 – All species are capable of producing more
offspring than their environment can support (all species have
the reproduction potential to increase their population size
exponentially if all individuals born reproduce)
Observation 4 – Owing to lack of food or to other resources, many
of these offspring do not survive (natural resources are limited)
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“The Origin of Species”
Inference 1 – individuals whose inherited traits give them a higher
probability of surviving and reproducing in a given environment
tend to leave more offspring than other individuals




More individuals are produced than the environment can support
leading to a struggle for existence with only a portion of
individuals surviving
Not everyone has the same success of reproducing
Those individuals whose inherited variations are better suited to
their environment are more likely to survive and reproduce
(passing on alleles to offspring)
Survival of the fittest – is not random but in based on the
environment
Inference 2 – This unequal ability of individuals to survive and
reproduce will lead to the accumulation of favorable traits in
the population over generations. Gradual change in a
population.
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AP Biology – Chapter 22
Natural Selection
  Variations arise by chance but natural selection is not




random since environmental factions set criteria for
reproductive success
Natural selection is possible due to variations and
over production
Individuals do NOT evolve – Populations evolve
Natural Selection can amplify or diminish only
heritable traits
Environmental factors vary from place to place over
time – the traits that are favored depend on the
environmental context
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Signs of Evolution
1.  Direct observations of Evolutionary Change
Direct observation of natural selection leading to
adaptive evolution in many studies

a.





Research on wild guppy populations – impact of predators
on guppies – guppies have variable color patterns
Color patterns controlled by genes that in the wild, are only
expressed by male guppies
Female guppies are attricated to male guppies with bright
colors
However bright colored guppies also attract predators
Observed that the color patterns of male guppies
corresponded with intensity of predation
Hypothesized that intense predation caused natural selection
to favor drab colors in male guppies
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Signs of Evolution
b.  Evolution of Drug-Resistant HIV





Evolution of drug resistant pathogens. Particular problem
with bacteria and viruses that reproduce rapidly - individuals
resistant to a particular drug can increase rapidly
HIV – numerous drugs to combat HIV, but using these
medications selects for viruses resistant to the drugs
Natural selection is a process of editing rather than a creative
mechanism
A drug does not create resistant pathogens, it selects for
resistant individuals that were already present in the
population
Natural selection depends on time and place – favors
characteristics that provide advantage in the current, local
environment
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AP Biology – Chapter 22
Natural selection
in action
MRSA
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Signs of Evolution
2.  Fossil Record

Sedimentary rock layers




Shows that past organisms differed from living organisms
Shows that many species have become extinct
Shows that species have evolved over time
Documents the origins of major new groups of organisms
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AP Biology
Why should extinct
species & living species
be found on the
same continent?
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AP Biology – Chapter 22
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
Mesohippus
Hyracotherium
150
100
50
Nannippus
60
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55 50
45 40
35
30 25 20 15 10 5 0
Millions of years ago
Signs of Evolution
3.  Homology




Characteristics present in an ancestral organism are
altered (by natural selection) in its decendants over
time  exposed to different environemntal conditions
Realted species can have characterisits with a similarity
even though they have different functions
Similarity resulting from common ancestry
Homologous Structures


Ex: Forelimbs of all mammals, including humans, cats,
whales, bats  show same arrangement of bones
Similar structure but very different function
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3. What are the lines of evidence that support Darwin’s ideas?
Anatomical evidence
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AP Biology – Chapter 22
Homologous structures
spines
leaves
succulent leaves
Don’t forget
our plant friends!
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needles
tendrils
colored leaves
Homology
  Analogous Structures
  Similar functions, NO common ancestor
  Ex: wings of a bird vs. butterfly wings
  Vestigial Structures
  Remnants of features that served important functions in
the organism’s ancestors
  No current use to the organisms (had a function in the
past)
  Ex: appendix (in humans)
  Molecular Biology
  Similarities among organisms at the molecular level
  DNA, RNA
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Analogous structures
Convergent
Don’t
be fooled
byevolution
their looks!
Those
& tails
Does fins
this mean
& sleek
they bodies
have a are
recent
common
ancestor?
analogous
structures
!
Solving a similar problem with a similar solution
AP Biology
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AP Biology – Chapter 22
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
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Evolutionary Tree
  Representation of the pattern of descent from
common ancestors and the resulting homology
  Diagram that reflects evolutionary relationships
among groups of organisms
  Figure 22.19 in your textbook
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Building “family” trees
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AP Biology – Chapter 22
Convergent Evolution
  The independent evolution of similar features in different
lineages
  Natural selection affects independently evolving species in
similar environments in similar ways
  Evolved independently from different ancestors, yet they have
adapted to similar environments in similar ways
  Resemblance is said to be analogous NOT homologous

Species share features but NO common ancestor
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Convergent evolution
These animals
look very similar but does
that mean they have a
recent common ancestor?
marsupial
mammals
What is this
evidence of?
placental
mammals
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Signs of Evolution
4.  Biogeography


Geographical distribution of species
Influenced by many factors:





Continental drift – slow movement of Earth’s
continents over time
About 250 million years ago these movements united
all of Earth’s landmasses into a single large continent,
called Pangea
200 million years ago Pangea began to break about
By 20 million years ago, the continents we know today
were within a few hundred kilometers of their current
locations
Use continental drift - Can predict where fossils of
different groups of organisms might be found
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AP Biology – Chapter 22
Biogeography
  Can also use our understanding of evolution to
explain biogehgraphic data


Endemic – islands generally have many species of
plants and animals that are endemic – they are found
nowhere else in the world
As Darwin explained in his book – most island species
are closely related to species found on the mainland
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Conclusion….
  What is theoretical about Darwin’s view
of life?
Darwin’s theory is supported by a large amount of
evidence
  Effects of natural selection can be seen and tested
in nature
  The word theory is much more than a hypothesis
  Darwin originally thought evolution was a slow
process
  Natural selection is not the only mechanism
responsible for evolution

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“There is grandeur in this view of
life….[in which] endless forms most beautiful and
most wonderful have been, and are being, evolved.”
Charles Darwin
The Origin of Species
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Campbell Chapters 22-24
13
AP Biology – Chapter 22
Review/Wrap Up Slides
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Big Idea 1
  The process of evolution drives the
diversity and unity of life
cells
DNA
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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
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AP Biology – Chapter 22
Evolution of birds
  Archaeopteryx


lived about 150 mya
links reptiles & birds
Smithsonian Museum,
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Washington,
DC
Evolution of land animals
  2006 Fossil Discovery of Early Tetrapod


“Tiktaalik”
“missing link” from sea to land animals
  from swimming (0 legs) to walking (4 legs)
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Evolution of
marine mammals
But then,
they actually
found my fossil!
At first,
I was just
a Biology
joke! AP
Land Mammal
?
?
e
re th
re a
Whe sitional
tran sils?
fos
?
?
Aquatic Mammal
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AP Biology – Chapter 22
2. What are the lines of evidence that support Darwin’s ideas?
Terminal
bud
Lateral
buds
Cabbage
Artificial selection
Brussels
sprouts
Leaves
Flower cluster
Kale
Cauliflower
Stem
Flower
and
stems
Broccoli
Wild mustard
Kohlrabi
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Selective
breeding
the raw genetic
material (variation)
is hidden there
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Parallel/convergent evolution
Niche
Burrower
Placental Mammals
Mole
Anteater
Anteater
Nocturnal
insectivore
Mouse
Climber
Australian Marsupials
Convergent evolution
of analogous
Marsupial mole
burrowing characteristics
Numbat
Marsupial mouse
Spotted cuscus
Lemur
Glider
Stalking
predator
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Chasing
predator
Flying
squirrel
Sugar glider
Ocelot
Tasmanian cat
Wolf
Tasmanian “wolf”
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AP Biology – Chapter 22
4. What are the lines of evidence that support Darwin’s ideas?
Human
Macaque
Dog Bird
Frog
Lamprey
The sequence in
Why&compare
DNA
proteins
is a molecular
DNA
& proteins
across
species?
record
of evolutionary
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
compare common genes
Number of amino acid differences
between
hemoglobin (146 aa) of vertebrate species and that
of humans C (respiration)
  cytochrome
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  hemoglobin (gas exchange)
"Nothing in biology
makes sense except in
the light of evolution."
-- Theodosius Dobzhansky
March 1973
Geneticist, Columbia University
(1900-1975)
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Evolution is "so overwhelmingly
established that it has become
irrational to call it a theory."
-- Ernst Mayr
What Evolution Is
2001
Professor Emeritus, Evolutionary Biology
Harvard University
(1904-2005)
AP Biology
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