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Chapter 14
Darwin and Evolution
14.1 Darwin’s Theory of Evolution
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Charles Darwin was 22 in 1831.
Naturalist aboard the HMS Beagle
5 year voyage through Southern Hemisphere
Mission to expand navy’s knowledge of natural
resources (water and food) in foreign lands
Observation led Darwin to conclude that
biological evolution occurs
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Contrary to current beliefs of his time
Figure 14.1 Voyage of the HMS Beagle.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Charles Darwin
HMS Beagle
marine iguana
Galápagos
Islands
rhea
(ship): © Mary Evans Picture Library/The Image Works; (iguana): © FAN Travelstock/Alamy RF;
(rhea): © Nicole Duplaix/National Geographic/Getty Images;
(Darwin): © American Museum of Natural History, photo courtesy Geoffrey West. Neg. #326697
• Before Darwin
 People had an entirely different way of viewing
the world.
• Earth only a few thousand years old
• Species remained the same since creation.
 Explorers brought back fossils (remains of
once-living organisms) found in strata (layers of
rock or sedimentary material).
 Georges Cuvier founded paleontology.
• Study of fossils
• He believed in fixity of species yet strata showed a
succession of different forms over time.
• Catastrophism—explains appearance of new forms
as replacing old forms due to local catastrophe
Figure 14.2 Strata in rock.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Visible strata
© Doug Sherman
 Jean-Baptiste de Lamarck
• Evolution occurred and that adaptation was the cause of
diversity
• Concluded more complex forms descended from less
complex forms
• Inheritance of acquired characteristics
 Use and disuse of a structure can bring about inherited change
 Long neck in giraffes developed from stretching to reach food
 Not supported—people who were blinded in an accident would
have blind children
 Modern genetics—phenotypic changes acquired during the
lifetime do not result in genetic changes that can be passed to
offspring
 Darwin’s ideas close to Lamarck BUT
• Species are suited to the environment through no will of their
own
• Natural selection is the means for speciation
• Darwin’s conclusions based on
 Study of geology, fossils, and biogeography
• Charles Lyell’s book Principles of Geology
 Evidence that the Earth was subject to slow but
continuous cycles of erosion and uplift
 Uniformitarianism—these slow changes occurred at a
uniform rate
• Darwin concluded the Earth must be very old
Figure 14.3a Formation of strata.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
rain
weathering
and erosion
runoff
sedimentation
ocean
geologic uplift
settling
• Darwin’s conclusions based on
 Study of geology and fossils
• Darwin collected fossils during his voyage that
differed from modern forms.
• Once he accepted that the Earth must be very old,
he began to think there was time for descent with
modification (evolution) to occur.
• Species are not fixed but change over time.
• Darwin’s conclusions based on
 Study of biogeography
• Study of the distribution of life-forms on Earth
• Compared animals of South America to England
• Did the Patagonian hare resemble a rabbit
because the 2 types of animals were adapted to
the same environment?
 Convergent evolution
Figure 14.5 The Patagonian hare and European rabbit.
 Study of biogeography (cont.)
• Galápagos Islands—off the coast of South America
 Too far from mainland for most terrestrial plants and
animals to colonize
 Species there slightly different from mainland forms
 Where did they come from? Why are they different?
• Finches
 Some were like mainland finches, others quite different
 Ground-dwelling finch beak size dependent on seed they
eat
 Tree-dwelling finch beak size and shape dependent on
their insect prey
 Could have descended from a mainland finch
 Speciation—formation of a new species—occurred
because the isolated population evolved independently
of the mainland population.
Figure 14.6 Galápagos finches.
 Study of biogeography (cont.)
• Galápagos Islands tortoises
 Each island also had its own type of tortoise.
 Long-necked tortoises in dry areas where food
scarce
 Short-necked tortoises in moist regions with
abundant food
 Adaptation—any characteristic that makes an
organism more suited to its environment
• Natural selection and adaptation
 Natural selection
• Mechanism for evolution
• Process that results in the evolution of organisms
well adapted to their environment
• Requires:
 Members of a population to have heritable variation
 More offspring produced than can be supported
 Individuals with favorable traits survive and reproduce
more than those lacking the traits
 Across generations, a larger proportion of the population
possesses the favorable traits and become adapted to
the environment
• Uses only variations resulting from genetic
changes
 No direction or anticipation of future needs
• Ongoing process—as environment changes,
suitability of adaptations changes
Figure 14.7 Variation in shells of
a marine snail, Liguus fascitus.
• Organisms vary in their traits
 Prior to Darwin, variations were considered
imperfections and ignored.
 Variations are essential to Darwin’s natural selection
process.
 Genes, together with the environment, determine
phenotype.
 Mutations, chromosomal rearrangements, and
assortment of chromosomes during meiosis and
fertilization can cause new variations to arise.
• Organisms struggle to exist
 Thomas Malthus said death and famine are inevitable
because the human population increases faster than
the food supply.
 Darwin applied this to all organisms.
• Organisms differ in fitness
 Fitness—reproductive success of an individual
relative to other members of the population
• Determined by comparing the number of surviving fertile
offspring produced by each member of a population
 Most-fit individuals capture the most resources and
convert into a larger number of viable offspring
 What determines fitness varies for different
populations.
 Artificial selection—humans choose particular traits
 In nature, interaction with the environment determines
fitness.
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Figure 14.9
Mechanism of
evolution.
Lamarck’s proposal
Originally, giraffes had
short necks.
Giraffes stretched their
necks in order to reach
food.
Darwin’s proposal
Originally, giraffe neck
length varied.
Struggle to exist causes
long-necked giraffes to
have the most offspring.
•Inheritance of
acquired
characteristics
NOT supported by
modern genetics
•Natural selection
With continual stretching, Due to natural selection,
most giraffes now have
most giraffes now have
long necks.
long necks.
• Organisms become adapted
 An adaptation may take many generations to
evolve.
 Manatees, penguins and sea turtles all have
flippers to move through the water.
• Convergent evolution
 Natural selection causes adaptive traits to be
increasingly represented in succeeding
generations.
 Other process for evolution (chapter 15)
 Only natural selection results in adaptation to
the environment.
Figure 14.10 Adaptations of the vampire bat.
• Darwin and Wallace
 After the HMS Beagle retuned to England in 1836,
Darwin waited 20 years to publish On the Origin of
Species.
• Gathered evidence to support his hypothesis
• Prompted to publish after reading similar hypothesis by
Wallace
 Alfred Russel Wallace
• Also an English naturalist and collector at home and abroad
• Conceived idea of “survival of the fittest”
• Sent essay to Darwin for comment
 Joint paper presented to Linnean Society
• Darwin presented an abstract of On the Origin of Species
• Wallace presented “On the Tendency of Varieties to Depart
Indefinitely from the Original Type”
• Announced to the world that species evolve through natural
selection with common descent
14.2 Evidence of Evolutionary Change
• Theory of evolution states that all living things
have a common ancestor but each is adapted to
a particular way of life
• Hypotheses become a scientific theory only
when a variety of evidence from independent
investigators supports the hypothesis.
• Theory of evolution is a unifying theme in
biology because it can explain so many different
observations in various fields of biology
• Fossil evidence
 Fossils trapped in rock strata are the fossil
record that tell us about the history of life.
 Succession of life-forms from the simple to
the more complex
 Find transitional links between groups
 Archaeopteryx fossils intermediate
between reptiles and birds
 Evolution of whales
Figure 14.12 Re-creation Archaeopteryx.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
wing
feathers
teeth
tail with
vertebrae
claws
© Joe Tucciarone/Interstellar Illustrations
Figure 14.14 Evolution of whales.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Present
10 MYA
Modern toothed whales
20 MYA
30 MYA
The reduced hind limbs of
Rodhocetus kasrani could not
have aided it in walking or
swimming. Rodhocetus swam with an
up-and-down motion, as do modern whales.
40 MYA
Ambulocetus natans
Probably walked on land (as do
modern sea lions) and swam by
flexing its backbone and paddling with
its hind limbs (as do modern otters).
50 MYA
60 MYA
Hypothetical
mesonychid
skeleton
• Biogeographical evidence
 Study of distribution of organisms throughout the
world
 Distribution consistent with hypothesis that, when
forms are related, they evolved in one locale and then
spread to accessible regions
 Darwin noted that South America lacks rabbits even
though environment is suitable
• Rabbits evolved elsewhere and had no means of reaching
South America.
 South America, Antarctica, and Australia connected
long ago
• Marsupials and placental mammals arose at that time.
• Marsupials only plentiful in Australia because it drifted away
separating them from competition with placental mammals
• Opossum only marsupial in the
Americas
• In some cases marsupial and
placental mammals resemble
each other.
 Supports hypothesis that evolution
is influenced by environment
Figure 14.15 Marsupials of Australia.
• Anatomical evidence
 Vestigial structures
• Anatomical features that are fully developed in one group of
organisms but reduced and nonfunctional in other similar
groups
• Most birds have well-developed wings; ostriches do not
• Whales and snakes have remnants of hip bones and legs.
• Humans have a tailbone.
• Presence explained by common descent hypothesis
 Homologous structures
• Anatomically similar structures are explainable by inheritance
from a common ancestor.
• All vertebrate forelimbs contain the same set of bones
organized in similar ways despite dissimilar functions.
• Analogous structures—structures serve the same function but
are not constructed similarly—bird and insect wings
Figure 14.16 Significance of structural similarities.
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bird
bat
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
whale
cat
Figure 14.16 Significance of
structural similarities,
continued.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
horse
human
Figure 14.15 Significance of
structural similarities,
continued.
• Homology shared by vertebrates extends
to their embryological development
 At some time during development, all
vertebrates have a postanal tail and paired
pharyngeal pouches.
• In fishes and amphibian larvae, pouches develop
into functioning gills.
• In humans, first pair of pouches becomes cavity of
middle ear and auditory tube, second pair
becomes tonsils, and third and fourth pair become
thymus and parathyroid glands
 New structures originate by modifying
preexisting structures of one’s ancestors.
Figure 14.17 Significance of developmental similarities.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chick embryo
Pig embryo
eye
pharyngeal
pouches
postanal
tail
(both): © CBS/Phototake
• Molecular evidence
 All living organisms use the same biochemical
molecules, including DNA, ATP, and many
nearly identical enzymes.
 Many developmental genes (Hox) are shared
in animals ranging from worms to humans.
 Life’s vast diversity has come about from only
slight differences in the same genes.
 Cytochrome c is a molecule used in the
electron transport chain of all organisms.
• Data on the amino acid sequence show that the
sequence varies consistent with other data
regarding anatomical similarities, and therefore
relatedness.
Figure 14.18 Significance of biochemical differences.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Types of Organisms
monkey
pig
duck
turtle
fish
moth
yeast (Candida)
0
10
20
30
40
50
Number of Amino Acid Differences Compared to Human Cytochrome c
human
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