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Charles Darwin

• 1859 Origin of Species published
• Argued from evidence that species inhabiting
  Earth today descended from ancestral species
• Proposed a mechanism for evolution ? Natural
  Selection
• Many scientists helped pave the way for Darwins
  Theory

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Fig. 22-2
Linnaeus (classification)
Hutton (gradual geologic change)
Lamarck (species can change)
Malthus (population limits)
Cuvier (fossils, extinction)
Lyell (modern geology)
Darwin (evolution, natural selection)
Wallace (evolution, natural selection)
American Revolution
French Revolution
U.S. Civil War
1900
1850
1800
1750
1795
Hutton proposes his theory of gradualism.
1798
Malthus publishes Essay on the Principle of
Population.
1809
Lamarck publishes his hypothesis of evolution.
1830
Lyell publishes Principles of Geology.
18311836
Darwin travels around the world on HMS Beagle.
1837
1837
Darwin begins his notebooks.
1844
Darwin writes essay on descent with modification.
1858
Wallace sends his hypothesis to Darwin.
1859
The Origin of Species is published.
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Lamarcks Hypothesis of Evolution

• Lamarck hypothesized that species evolve through
  use and disuse of body parts and the inheritance
  of acquired characteristics
• The mechanisms he proposed are unsupported by
  evidence

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• Charles Darwin had a consuming interest in nature
• First studied medicine (unsuccessfully), and then
  theology at Cambridge University
• After graduating, he took an unpaid position as
  naturalist and companion to Captain Robert
  FitzRoy for a 5-year around the world voyage on
  the Beagle

GREAT BRITAIN
EUROPE
NORTH AMERICA
ATLANTIC OCEAN
The Galápagos Islands
AFRICA
Pinta
Genovesa
Equator
Marchena
SOUTH AMERICA
Santiago
Daphne Islands
AUSTRALIA
Pinzón
Fernandina
PACIFIC OCEAN
Cape of Good Hope
Andes
Isabela
Santa Cruz
Santa Fe
San Cristobal
Tasmania
Florenza
Española
Cape Horn
New Zealand
Tierra del Fuego

• During his travels on the Beagle, Darwin
  collected specimens of South American plants and
  animals
• He observed adaptations of plants and animals
  that inhabited many diverse environments

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• The most influential stop on the voyage was to
  the Galápagos Islands
• Darwin noticed that many of the birds and
  reptiles were unique to specific islands in the
  Galápagos archipelago
• These included tortoises

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Fig. 22-6
(a) Cactus-eater
(c) Seed-eater
(b) Insect-eater
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• In the Darwinian view, the history of life is
  like a tree with branches representing lifes
  diversity
• Darwins theory meshed well with the hierarchy of
  Linnaeus

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Artificial Selection, Natural Selection, and
Adaptation

• Darwin noted that humans have modified other
  species by selecting and breeding individuals
  with desired traits, a process called artificial
  selection
• Darwin then described four observations of nature
  and from these drew two inferences

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Fig. 22-9
Terminal bud
Lateral buds
Cabbage
Brussels sprouts
Flower clusters
Leaves
Kale
Cauliflower
Stem
Wild mustard
Flowers and stems
Kohlrabi
Broccoli
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• Observation 1 Members of a population often
  vary greatly in their traits

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• Observation 2 Traits are inherited from parents
  to offspring
• Observation 3 All species are capable of
  producing more offspring than the environment can
  support
• Observation 4 Owing to lack of food or other
  resources, many of these offspring do not survive

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• An example of the process of evolution
• Some populations of head lice wont be killed by
  the chemical permethrin, a common treatment
• Studies have shown that this evolution occurred
  after only about 30 months (40 generations of
  lice)

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The Process of Evolution

• Individuals DO NOT evolve
• One louse did not, all of a sudden, have the
  ability to stay alive when permethrin was in the
  environment
• The resistance that developed was genetic, passed
  on from one generation to the next

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Fig. 22-12
(a) A flower mantid in Malaysia
(b) A stick mantid in Africa
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Direct Observations of Evolutionary Change

• New discoveries continue to fill the gaps
  identified by Darwin in The Origin of Species
• Examples provide evidence for natural selection
• the effect of differential predation on guppy
  populations
• evolution of drug-resistant HIV
• Antibiotic resistance in bacteria
• Pesticide resistance in insects

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Fig. 22-13
EXPERIMENT
Predator Killifish preys mainly on
juvenile guppies (which do not express the color
genes)
Experimental transplant of guppies
Pools with killifish, but no guppies prior to
transplant
Guppies Adult males have brighter colors than
those in pike-cichlid pools
Predator Pike-cichlid preys mainly on adult
guppies
Guppies Adult males are more drab in color than
those in killifish pools
RESULTS
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12
10
10
8
8
Area of colored spots (mm2)
Number of colored spots
6
6
4
4
2
2
0
0
Source population
Transplanted population
Source population
Transplanted population
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Fig. 22-14
100
Patient No. 1
Patient No. 2
75
Percent of HIV resistant to 3TC
50
Patient No. 3
25
0
2
0
4
6
8
10
12
Weeks
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Fig. 22-UN2
Insecticide Resistance
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• Natural selection does not create new traits, but
  edits or selects for traits already present in
  the population
• The local environment determines which traits
  will be selected for or selected against in any
  specific population

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1. The Fossil Record
There are 5 major pieces of evidence that
supports the theory of evolution

• The fossil record provides evidence of the
  extinction of species, the origin of new groups,
  and changes within groups over time

(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
(c) Dorudon (fully aquatic)
(d) Balaena (recent whale ancestor)
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Fig. 22-8
Hyracoidea (Hyraxes)
Sirenia (Manatees and relatives)
Moeritherium
Barytherium
Deinotherium
Mammut
Platybelodon
Stegodon
Mammuthus
Elephas maximus (Asia)
Loxodonta africana (Africa)
Loxodonta cyclotis (Africa)
0
104
5.5
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2
24
Millions of years ago
Years ago
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Fig. 22-17
2. Homologous structures are anatomical
resemblances that represent variations on a
structural theme present in a common ancestor
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Whale
Cat
Bat
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Homologous Structures

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• 3. Biochemical Evidence
• Molecular level ? genes shared among organisms
  inherited from a common ancestor

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Fig. 22-18
Pharyngeal pouches
Post-anal tail
Human embryo
Chick embryo (LM)
4. Comparative embryology reveals anatomical
homologies not visible in adult organisms
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• 5. Vestigial structures are remnants of features
  that served important functions in the organisms
  ancestors

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Convergent Evolution

• Convergent evolution is the evolution of similar,
  or analogous, features in distantly related
  groups
• Analogous traits arise when groups independently
  adapt to similar environments in similar ways
• Convergent evolution does not provide information
  about ancestry

Sugar glider
Flying squirrel
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Fig. 22-19
Branch point (common ancestor)
Lungfishes
Amphibians
1
Tetrapods
Mammals
2
Tetrapod limbs
Amniotes
Lizards and snakes
3
Amnion
4
Crocodiles
Homologous characteristic
5
Ostriches
Birds
6
Feathers
Hawks and other birds
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Population Genetics

• The genetic structure of a population is defined
  by its allele and genotype frequencies
• Hardy Weinberg Theorem describes non-evolving
  populations

• The 5 causes of microevolution are
• Genetic drift
• Gene flow
• Mutation
• Nonrandom mating
• Natural selection

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Genetic drift

• Changes in the gene pool of a small population
  due to chance
• The larger the population less drift

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• 2 situations which result in populations small
  enough for genetic drift to be important are
• Bottleneck effect
• (population is reduced by natural disasters)
  (ex. Cheetah)
• Founder effect
• ( few individuals colonize new habitat) (ex.
  Amish)

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The Bottleneck Effect

• The bottleneck effect is a sudden reduction in
  population size due to a change in the
  environment
• The resulting gene pool may no longer be
  reflective of the original populations gene pool
• If the population remains small, it may be
  further affected by genetic drift

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The Founder Effect

• The founder effect occurs when a few individuals
  become isolated from a larger population
• Allele frequencies in the small founder
  population can be different from those in the
  larger parent population

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Case Study Impact of Genetic Drift on the
Greater Prairie Chicken
Post-bottleneck (Illinois, 1993)
Pre-bottleneck (Illinois, 1820)
Researchers used DNA from museum specimens to
compare genetic variation in the population
before and after the bottleneck The results
showed a loss of alleles at several
loci Researchers introduced greater prairie
chickens from population in other states and were
successful in introducing new alleles and
increasing the egg hatch rate to 90
Loss of prairie habitat caused a severe reduction
in the population of greater prairie chickens in
Illinois The surviving birds had low levels of
genetic variation, and only 50 of their eggs
hatched
Range of greater prairie chicken
(a)
Percentage of eggs hatched
Number of alleles per locus
Population size
Location
Illinois
5.2 3.7
93 lt50
19301960s
1,00025,000
1993
lt50
Kansas, 1998     (no bottleneck)
750,000
5.8
99
Nebraska, 1998     (no bottleneck)
75,000 200,000
5.8
96
Minnesota, 1998     (no bottleneck)
4,000
5.3
85
(b)
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Effects of Genetic Drift A Summary

1. Genetic drift is significant in small populations
2. Genetic drift causes allele frequencies to change
   at random
3. Genetic drift can lead to a loss of genetic
   variation within populations
4. Genetic drift can cause harmful alleles to become
   fixed

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Gene Flow

• Alleles can be transferred through the movement
  of fertile individuals or gametes (for example,
  pollen)
• Gene flow tends to reduce differences between
  populations over time
• Gene flow is more likely than mutation to alter
  allele frequencies directly
• Effects of GMOs on environment?

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• Gene flow can decrease the fitness of a
  population
• In bent grass, alleles for copper tolerance are
  beneficial in populations near copper mines, but
  harmful to populations in other soils
• Windblown pollen moves these alleles between
  populations
• The movement of unfavorable alleles into a
  population results in a decrease in fit between
  organism and environment

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MINE SOIL
NON- MINE SOIL
NON- MINE SOIL
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50
Prevailing wind direction
Index of copper tolerance
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30
20
10
0
20
0
20
0
20
40
60
80
100
120
140
160
Distance from mine edge (meters)
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• Gene flow can increase the fitness of a
  population
• Insecticides have been used to target mosquitoes
  that carry West Nile virus and malaria
• Alleles have evolved in some populations that
  confer insecticide resistance to these mosquitoes
• The flow of insecticide resistance alleles into a
  population can cause an increase in fitness

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Mutations

• A new mutation that is transmitted in gametes can
  change the gene pool by substituting one allele
  for another
• Does not have a quantitative effect
• Is the original source of variation

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Mate Choice
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• Intrasexual selection is competition among
  individuals of one sex (often males) for mates of
  the opposite sex
• Intersexual selection, often called mate choice,
  occurs when individuals of one sex (usually
  females) are choosy in selecting their mates
• Male showiness due to mate choice can increase a
  males chances of attracting a female, while
  decreasing his chances of survival (sexual
  dimorphism)

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Fig. 23-13
Three modes of selection
Original population
Frequency of individuals
Phenotypes (fur color)
Original population
Evolved population
(c) Stabilizing selection
(b) Disruptive selection
(a) Directional selection
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If the Siberian Husky had heavier muscles, it
would sink deeper into the snow, so they would
move slower or would sink and get stuck in the
snow. Yet if the Siberian Husky had lighter
muscles, it would not be strong enough to pull
sleds and equipment, so the dog would have little
value as a working dog
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Peppered Moth Biston betularia

• Industrial melanism study by Kettlewell

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Patterns of Macroevolution
Convergent evolution
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Coevolution

• Mantismimicry http//www.pbs.org/wgbh/evolution/l
  ibrary/01/1/l_011_03.html

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Orchid and Bee coevolution http//www.pbs.org/wgb
h/evolution/library/01/1/l_011_02.html
example of mimicry in which the orchid has
evolved to resemble a female bee
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Crab spider

• coevolution

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Adaptive radiation
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Extinction
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• Gradualism

The interval between speciation events can range
from 4,000 years (some cichlids) to 40,000,000
years (some beetles), with an average of
6,500,000 years
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Why Natural Selection Cannot Fashion Perfect
Organisms

1. Selection can act only on existing variations
2. Evolution is limited by historical constraints
3. Adaptations are often compromises
4. Chance, natural selection, and the environment
   interact

Loud call great for calling females but also
great for calling predators
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The Biological Species Concept

• The biological species concept states that a
  species is a group of populations whose members
  have the potential to interbreed in nature and
  produce viable, fertile offspring they do not
  breed successfully with other populations
• Gene flow between populations holds the phenotype
  of a population together

(a) Similarity between different species
(b) Diversity within a species
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Fig. 24-4a
Prezygotic barriers
Habitat Isolation
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Individuals of different species
Mating attempt
(f)
(e)
(a)
(c)
(d)
(b)
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Fig. 24-4i
Prezygotic barriers
Postzygotic barriers
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown
Gametic Isolation
Viable, fertile offspring
Fertilization
(h)
(g)
(l)
(i)
(j)
(k)
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Limitations of the Biological Species
ConceptWhat is a species?

• The biological species concept
• Reproductively isolated
• cannot be applied to fossils or asexual organisms
  (including all prokaryotes)

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Other Definitions of Species

• Other species concepts emphasize the unity within
  a species rather than the separateness of
  different species
• The morphological species concept defines a
  species by structural features
• It applies to sexual and asexual species but
  relies on subjective criteria

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• The ecological species concept views a species in
  terms of its ecological niche
• It applies to sexual and asexual species and
  emphasizes the role of disruptive selection
• The phylogenetic species concept defines a
  species as the smallest group of individuals on a
  phylogenetic tree (molecular sequences)
• It applies to sexual and asexual species, but it
  can be difficult to determine the degree of
  difference required for separate species

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Fig. 24-5
gene flow is interrupted or reduced when a
population is divided into geographically
isolated subpopulations
speciation takes place in geographically
overlapping populations
(a) Allopatric speciation
(b) Sympatric speciation
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Fig. 24-6
A. harrisi
A. leucurus
Regions with many geographic barriers typically
have more species than do regions with fewer
barriers
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Reproductive isolation between populations
generally increases as the distance between them
increases
2.0
1.5
Degree of reproductive isolation
1.0
0.5
0
0
50
100
150
250
200
300
Geographic distance (km)