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Basic Evolutionary Concepts
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Clown, Fool, or Simply Well Adapted?
• All organisms have evolutionary adaptations
– Inherited characteristics that enhance their
ability to survive and reproduce
• The blue-footed booby of the
Galápagos Islands has features
that help it succeed in its
environment
– Large, webbed feet help
propel the bird through
water at high speeds
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– A streamlined shape, large tail, and nostrils that
close are useful for diving
– Specialized salt-secreting glands manage salt
intake while at sea
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EVIDENCE OF EVOLUTION
13.1 A sea voyage helped Darwin frame his theory
of evolution
• Aristotle and the Judeo-Christian culture
believed that species are fixed
• Fossils suggested that life forms change
– This idea was embraced by Lamarck in the early
1800s
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• While on the voyage of the HMS Beagle in the
1830s, Charles Darwin observed
– similarities between living and fossil organisms
– the diversity of life on the Galápagos Islands,
such as blue-footed boobies and giant tortoises
Figure 13.1A
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• The voyage of the Beagle
Great
Britain
Europe
North
America
Pacific
Ocean
Atlantic
Ocean
Africa
Galápagos
Islands
Equator
South
America
Australia
Cape of
Good Hope
Tasmania
Cape Horn
Tierra del Fuego
New
Zealand
Figure 13.1B
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• Darwin became convinced that the Earth was
old and continually changing
– He concluded that living things also change, or
evolve over generations
– He also stated that living species descended
from earlier life-forms: descent with
modification
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13.2 The study of fossils provides strong evidence
for evolution
• Fossils and the fossil record
strongly support the theory of
evolution. Incomplete but
valuable, preserves only hard
tissues
– Hominid skull
– Petrified trees
Figure 13.2A, B
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– Ammonite casts
– Fossilized organic
matter in a leaf
Figure 13.2C, D
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– Scorpion in amber
– “Ice Man”
Figure 13.2E, F
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• The fossil record shows that
organisms have appeared in a
historical sequence
• Many fossils link
early extinct species
with species living
today
– These fossilized
hind leg bones link
living whales with
their land-dwelling
ancestors
Figure 13.2G, H
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13.3 A mass of evidence validates the evolutionary
view of life
• Other evidence for evolution comes from
– Biogeography:
impact of geographic
barriers and continental drift
– Comparative
anatomy and
embryology
– analogous and
vestigal structures
Human
Cat
Whale
Bat
Figure 13.3A
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– Molecular biology: examines similarities
between molecules, estimates divergence
Human
Rhesus monkey
Last common
ancestor lived
26 million years
ago (MYA),
based on
fossil evidence
Mouse
Chicken
Frog
Lamprey
80 MYA
275 MYA
330 MYA
450 MYA
Figure 13.3B
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DARWIN’S THEORY AND THE MODERN
SYNTHESIS
13.4 Darwin proposed natural selection as the
mechanism of evolution through differential
reproduction
• Darwin observed that
– Reproduction: organisms produce more
offspring than the environment can support
– Variation: organisms vary in many
characteristics
– Inheritance: these variations can be inherited
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• Darwin concluded that individuals best suited
for a particular environment are more likely to
survive and reproduce than those less well
adapted
• Darwin saw natural selection as the basic
mechanism of evolution
– As a result, the proportion of individuals with
favorable characteristics increases
– Populations gradually change in response to the
environment
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• Darwin also saw that when
humans choose organisms
with specific characteristics as
breeding stock, they are
performing the role of the
environment
– This is called artificial
selection
– Example of artificial
selection in plants: five
vegetables derived from one
species: wild mustard
Figure 13.4A
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– Example of artificial selection in animals: dog
breeding
German shepherd
Yorkshire terrier
English springer
spaniel
Mini-dachshund
Golden retriever
Hundreds to
thousands of years
of breeding
(artificial selection)
Ancestral dog
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Figure 13.4B
• These five canine species evolved from a
common ancestor through natural selection
African wild
dog
Coyote
Fox
Wolf
Jackal
Thousands to
millions of years
of natural selection
Ancestral canine
Figure 13.4C
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13.5 Connection: Scientists can observe natural
selection in action
• Evolutionary adaptations have been observed
in populations of birds, insects, and many other
organisms
– Example: camouflage adaptations of mantids
that live in different environments
Figure 13.5A
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• The evolution of insecticide resistance is an
example of natural selection in action
Insecticide
application
Chromosome with gene
conferring resistance
to insecticide
Additional
applications of the
same insecticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Survivor
Figure 13.5B
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13.7 Microevolution is change in a population’s
gene pool over time
• A gene pool is the total collection of genes in a
population at any one time
• Microevolution is a change in the relative
frequencies of alleles in a gene pool
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13.11 There are several potential causes of
microevolution
• Genetic drift
is a change in a
gene pool due
to chance
– Genetic drift
can result in
the
bottleneck
effect
Original
population
Bottlenecking
event
Surviving
population
Figure 13.11A
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– or the founder effect
Figure 13.11B, C
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• Gene flow can change a gene pool due to the
movement of genes into or out of a population
• Mutation changes alleles
• Natural selection leads to differential
reproductive success
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13.12 Adaptive change results when natural
selection upsets genetic equilibrium
• Natural selection results in the accumulation of
traits that adapt a population to its environment
– If the environment should change, natural
selection would favor traits adapted to the new
conditions
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13.16 Not all genetic variation may be subject to
natural selection
• Some variations may be neutral, providing no
apparent advantage or disadvantage
– Example: human fingerprints
Figure 13.16
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13.17 Connection: Endangered species often have
reduced variation
• Low genetic variability may reduce the
capacity of endangered species to survive as
humans continue to alter the environment
– Studies have shown that cheetah populations
exhibit extreme genetic uniformity
– Thus they may have a
reduced capacity to
adapt to environmental
challenges
Figure 13.17
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13.18 The perpetuation of genes defines
evolutionary fitness
• An individual’s Darwinian fitness is the
contribution it makes to the gene pool
of the next generation relative to the
contribution made by other individuals
• Production of fertile offspring is the
only score that counts in natural
selection
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13.20 Sexual selection may produce sexual
dimorphism
• Sexual selection leads to the evolution of
secondary sexual characteristics
– These may give individuals an advantage in
mating
Figure 13.20A, B
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13.22 Connection: The evolution of antibiotic
resistance in bacteria is a serious public
M
health concern
• The excessive use of antibiotics is leading to the
evolution of antibiotic-resistant bacteria
– Example:
Mycobacterium
tuberculosis
Figure 13.22
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• One example of rapid evolution occurred
among mosquitoes who migrated into the
London underground
• In less than 150
years, Culex pipiens
evolved into a new
mosquito species,
Culex molestus
• The origin of new
species is called
speciation
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• The isolated mosquitoes adapted to their new
underground environment
– They altered their prey, mating habits, and
breeding patterns
• Environmental barriers that isolate
populations are just one of many mechanisms
in the evolution of species
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MECHANISMS OF SPECIATION
14.3 Geographic isolation can lead to speciation
• When a population is cut off from its parent
stock, species evolution may occur
– An isolated population may become genetically
unique as its gene pool is changed by natural
selection, genetic drift, or mutation
– This is called allopatric speciation
Figure 14.3
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14.4 Islands are living laboratories of speciation
• On the
Galápagos
Islands,
repeated
isolation and
adaptation
have resulted
in adaptive
radiation of
14 species of
Darwin’s
finches
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Figure 14.4A
14.5 New species can also arise within the same
geographic area as the parent species
• In sympatric speciation, a new species may
arise without geographic isolation
– A failure in meiosis can produce diploid gametes
– Self-fertilization can then produce a tetraploid
zygote
Parent species
Zygote
Meiotic
error
Selffertilization
2n = 6
Diploid
Offspring may
be viable and
self-fertile
4n = 12
Tetraploid
Unreduced diploid gametes
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Figure 14.5A
14.6 Connection: Polyploid plants clothe and
feed us
• Many plants are polyploid
– They are the products of
hybridization
– The modern bread wheat
is an example
Figure 14.6A
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Evolutionary Tree
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Historical Time Line
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One Possible Human Genealogy
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Ancestors
• Australopithecus afarensis: upright primate, vegetarian,
sexual dimorphism, 4-5 million years ago
• Homo habilis: first tool maker, enlarged brain, omnivore,
decline in sexual dimorphism, 2.6 million years ago
• Homo erectus: more brain enlargement, longer infancy,
continued decline in sexual dimorphism, continued tool
development, continued social development, spread out of
Africa to Europe and Asia, 2 million years ago
• Homo neanderthalensis: may be an extinct branch
• Homo sapien: only surviving Homo species, 100,000 to
140,000 years ago
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Racial Differences
• Racial differences are slight differences in
phenotypes between subgroups of a common
species
• Advantages
– Dark skin: protection from ultraviolet (UV)
damage in intensive sunlight
– Light skin: allows adequate UV radiation for
Vitamin D production in less intense sunlight
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings