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Charles Darwin
•
1859 – “Origin of Species”
published
1. Argued from evidence that species
inhabiting Earth today descended
from ancestral species
2. Proposed a mechanism for
evolution  Natural Selection
•
Many scientists helped pave the way
for Darwin’s Theory
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
1800
1900
1750
1850
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.
1831–1836 Darwin travels around the world on HMS Beagle.
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.
Ideas About Change over Time
• The study of fossils
helped to lay the
groundwork for
Darwin’s ideas
• Fossils are remains or
traces of organisms
from the past, usually
found in sedimentary
rock, which appears in
layers or strata
Lamarck’s 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
•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
Santiago
Fernandina
Isabela
Daphne
Islands
Pinzón
Santa
Santa
Cruz
Fe
Florenza
SOUTH
AMERICA
AUSTRALIA
PACIFIC
OCEAN
San
Cristobal
Cape of
Good Hope
Tasmania
Española
Cape Horn
Tierra del Fuego
New
Zealand
•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
•
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…
Fig. 22-6
(a) Cactus-eater
(c) Seed-eater
(b) Insect-eater
• In 1844, Darwin wrote an essay on the origin of
species and natural selection but did not
introduce his theory publicly, anticipating an
uproar
• 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 The Origin of Species
and published it the next year
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Origin of Species
• Darwin developed two main ideas:
– Descent with modification explains life’s
unity and diversity
• Darwin never used the word evolution in the first
edition of The Origin of Species
• He called it descent with modification  all
organisms are related through descent from an
ancestor that lived in the remote past
– Natural selection is a cause of adaptive
evolution
• In the Darwinian view,
the history of life is like
a tree with branches
representing life’s
diversity
• Darwin’s theory meshed
well with the hierarchy
of Linnaeus
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
Fig. 22-9
Terminal
bud
Lateral
buds
Cabbage
Brussels sprouts
Flower
clusters
Leaves
Kale
Cauliflower
Stem
Wild mustard
Flowers
and stems
Broccoli
Kohlrabi
• Observation #1: Members of a population often
vary greatly in their traits
• 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
• 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
• Inference #2: This unequal ability of individuals
to survive and reproduce will lead to the
accumulation of favorable traits in the
population over generations
An example of the process of evolution:
•
Some populations of head lice won’t 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)
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
Fig. 22-12
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
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
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
12
Number of
colored spots
12
10
8
6
4
2
0
Source
population
Transplanted
population
10
8
6
4
2
0
Source
population
Transplanted
population
Fig. 22-14
100
Patient
No. 1
Patient No. 2
75
50
Patient No. 3
25
0
0
2
4
6
Weeks
8
10
12
Fig. 22-UN2
Insecticide Resistance
• 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
There are 5 major pieces of evidence that
supports the theory of evolution
1. The Fossil Record
(a) Pakicetus (terrestrial)
• The fossil record
provides evidence of
the extinction of
species, the origin of
new groups, and
changes within
groups over time
(b) Rhodocetus (predominantly aquatic)
(c) Dorudon (fully aquatic)
(d) Balaena
(recent whale ancestor)
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)
34
24
Millions of years ago
5.5
2 104 0
Years ago
Fig. 22-17
Homologous structures are anatomical
resemblances that represent variations on a structural
theme present in a common ancestor
2.
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
Homologous Structures
• 3. Biochemical Evidence
– Molecular level  genes
shared among organisms
inherited from a common
ancestor
Fig. 22-18
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
4. Comparative embryology reveals anatomical
homologies not visible in adult organisms
5. Vestigial structures are remnants of features
that served important functions in the organism’s
ancestors
Homologies and “Tree Thinking”
• The Darwinian concept of an evolutionary
tree of life can explain homologies
• Evolutionary trees are hypotheses about the
relationships among different groups
• Evolutionary trees can be made using different
types of data, for example, anatomical and
DNA sequence data
Fig. 22-19
Branch point
(common ancestor)
Lungfishes
Amphibians
1
Mammals
2
Tetrapod limbs
Amnion
Lizards
and snakes
3
4
Homologous
characteristic
Crocodiles
Ostriches
6
Feathers
Hawks and
other birds
Birds
5
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
• Earth’s continents were
formerly united in a
single large continent
called Pangaea, but
have since separated by
continental drift
• An understanding of
continent movement and
modern distribution of
species allows us to
predict when and where
different groups evolved
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
Genetic
drift
•
Changes in the gene pool of a small population due to
chance
•
The larger the population = less drift
• 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)
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 population’s gene pool
•
If the population remains small, it may be
further affected by genetic drift
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
Case Study: Impact of
Genetic Drift on the
Greater Prairie
Chicken
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
Pre-bottleneck Post-bottleneck
(Illinois, 1820) (Illinois, 1993)
Range
of greater
prairie
chicken
(a)
Location
Population
size
Percentage
Number
of alleles of eggs
per locus hatched
Illinois
1,000–25,000
5.2
93
<50
3.7
<50
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
1930–1960s
1993
(b)
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%
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
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 GMO’s on
environment?
•
•
•
•
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
70
60
MINE
SOIL
NONMINE
SOIL
NONMINE
SOIL
50
Prevailing wind direction
40
30
20
10
0
20
0
20
0
20
40
60
80
Distance from mine edge (meters)
100
120
140
160
• 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
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
Nonrandom mating
• Increases # of
homozygous loci in a
population, but does not
alter frequencies of allele’s
in gene pool
• 2 kinds:
–
Inbreeding (results in
higher frequency of homo
rec. individuals)
–
Assortive mating
(individuals prefer similar
phenotypic characters)
(ex. Size, color)
Natural selection
• Due to selection, alleles
are passed on to the next
generation in a
disproportionate numbers
relative to their
frequencies in the
present generation
• The only agent of
microevolution that is
adaptive, since it
accumulates and
maintains favorable
genotypes
Natural selection is the only mechanism that
consistently causes adaptive evolution
• Only natural selection consistently results in
adaptive evolution
• Natural selection brings about adaptive evolution
by acting on an organism’s phenotype
• The phrases “struggle for existence” and “survival
of the fittest” are misleading as they imply direct
competition among individuals
• Reproductive success is generally more subtle
and depends on many factors
Fig. 23-13
Three modes of selection
Original population
Original
Evolved
population population
(a) Directional selection
Phenotypes (fur color)
(b) Disruptive selection
(c) Stabilizing
selection
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
Peppered Moth: Biston betularia
• Industrial melanism study by Kettlewell
Genetic Drift
Convergent evolution
Convergent
evolution
Evolution of Camouflage
• Mantis:mimicry
http://www.pbs.org/wg
bh/evolution/library/01/
1/l_011_03.html
Orchid and Bee: coevolution
http://www.pbs.org/wgbh/evolution/library/01/1/l_011_02.html
exampl
e of
mimicr
y in
which
the
orchid
has
evolve
d to
Crab spider:
Sexual Selection
• Sexual selection is natural selection for
mating success
• It can result in sexual dimorphism, marked
differences between the sexes in secondary
sexual characteristics
• 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 male’s chances of
attracting a female, while
decreasing his chances of
survival
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
The Biological Species Concept
• The biological species
concept states that a
species is a group of
populations whose
(a) Similarity between different species
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
(b) Diversity within a species
Reproductive Isolation
• Reproductive isolation is the existence of
biological factors (barriers) that impede two
species from producing viable, fertile offspring
• Hybrids are the offspring of crosses between
different species
• Reproductive isolation can be classified by
whether factors act before or after fertilization
Fig. 24-4a
Prezygotic barriers
Habitat Isolation
Temporal Isolation
Individuals
of
different
species
(a)
Mating
attempt
(c)
(d)
(b)
Mechanical Isolation
Behavioral Isolation
(e)
(f)
Fig. 24-4i
Prezygotic barriers
Gametic Isolation
Postzygotic barriers
Reduced Hybrid Viability Reduced Hybrid Fertility
Hybrid Breakdown
Viable,
fertile
offspring
Fertilization
(g)
(h)
(i)
(j)
(k)
(l)
Limitations of the Biological Species Concept
• The biological species concept cannot be
applied to fossils or asexual organisms
(including all prokaryotes)
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
• 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
– It applies to sexual and asexual species, but it
can be difficult to determine the degree of
difference required for separate species
Concept 24.2: Speciation can take place with or
without geographic separation
• Speciation can occur in two ways:
– Allopatric speciation
– Sympatric speciation
Fig. 24-5
gene flow is
interrupted or
reduced when a
population is divided
into geographically
isolated
subpopulations
(a) Allopatric speciation
speciation takes
place in
geographically
overlapping
populations
(b) Sympatric speciation
Fig. 24-6
A. harrisi
A. leucurus
Regions with many geographic barriers
typically have more species than do regions
with fewer barriers
Degree of reproductive isolation
Reproductive isolation between populations generally
increases as the distance between them increases
2.0
1.5
1.0
0.5
0
0
50
200
250
100
150
Geographic distance (km)
300
Sexual Selection
• Sexual selection can drive sympatric speciation
• Sexual selection for mates of different colors
has likely contributed to the speciation in cichlid
fish in Lake Victoria
Fig. 24-12
EXPERIMENT
Normal light
P.
pundamilia
P. nyererei
Monochromatic
orange light
Allopatric and Sympatric Speciation: A Review
• In allopatric speciation, geographic isolation
restricts gene flow between populations
• Reproductive isolation may then arise by
natural selection, genetic drift, or sexual
selection in the isolated populations
• Even if contact is restored between
populations, interbreeding is prevented
• In sympatric speciation, a reproductive barrier
isolates a subset of a population without
geographic separation from the parent species
• Sympatric speciation can result from
polyploidy, natural selection, or sexual
selection
Concept 24.4: Speciation can occur rapidly or slowly
and can result from changes in few or many genes
• Many questions remain concerning how long it
takes for new species to form, or how many
genes need to differ between species
The Time Course of Speciation
• Broad patterns in speciation can be studied
using the fossil record, morphological data, or
molecular data
Patterns in the Fossil Record
• The fossil record includes examples of species
that appear suddenly, persist essentially
unchanged for some time, and then apparently
disappear
• Niles Eldredge and Stephen Jay Gould coined
the term punctuated equilibrium to describe
periods of apparent stasis punctuated by
sudden change
• The punctuated equilibrium model contrasts
with a model of gradual change in a species’
existence
Fig. 24-17
(a) Punctuated pattern
Time
(b) Gradual pattern
Speciation Rates
• The punctuated pattern in the fossil record and
evidence from lab studies suggests that
speciation can be rapid
• 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