Concepts of Biology 2nd Edition

1. Chapter 13
Darwin and
Evolution
Lecture Outline
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2. 13-2
Darwin Developed a Natural
Selection Hypothesis

3. Darwin made a trip around the world
Georges Cuvier knew that fossils showed a
succession of different life-forms through time
 Paleontology – the study of fossils
Jean-Baptiste de Lamarck concluded on the
basis of fossil evidence that more complex
organisms are descended from less complex
organisms
13-3

4. 13-4
Figure 13.1A One of the animals that Cuvier reconstructed from
fossils was the mastodon

5. 13-5
Figure 13.1B Lamarck thought the long neck of a giraffe was due
to continued stretching in each generation

6.  December 1831 a 22-year-old naturalist named
Charles Darwin (1809–1882) set sail on the
British naval vessel HMS Beagle
 Primary mission to expand navy’s knowledge of
natural resources in foreign lands
 Darwin made many observations about
similarities and differences among animals in
different parts of the world
13-6

7.  Darwin also collected fossils
 Sediments deposited in strata
 Darwin was convinced that the Earth’s massive
geologic changes are the result of slow
processes and that, therefore, in contrast to
thought at that time, the Earth was old enough to
have allowed evolution to occur
13-7

8. 13-8
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ATLANTIC
OCEAN
Europe
Africa
Australia
HMS Beagle
Tropical rain forest
Rhea
Charles Darwin, age 31
Marine iguanaWoodpecker finch
Patagonian desert Earth’s strata contain fossils
INDIAN
OCEAN
South
America
Great
Britain
North
America
PACIFIC
OCEAN
Galápagos
Islands
(rhea): © Nicole Duplaix/National Geographic/Getty Images; (desert): © C. Luiz Claudio Marigo/Peter Arnold/Photolibrary; (rain forest): © Chad Ehlers/Getty Images; (Darwin): © Carolina
Biological/Visuals Unlimited; (iguana): © Sami Sarkis/Getty RF; (finch): © D. Parer & E. Parer-Cook/Ardea; (strata): © Anthony L. Solis/Getty RF

9. Artificial selection mimics natural selection
 Darwin made a study of artificial selection
 Process by which humans choose, on the basis of
certain traits, the animals and plants that will
reproduce
 Example: Foxes are very shy and normally shun
people, but Russian scientists have produced silver
foxes that are pets
 Example: Several varieties of vegetables can be
traced to a single ancestor that exhibits various
characteristics
13-9

10. 13-10
Figure 13.2A Artificial selection has produced domesticated
foxes

11. 13-11
Figure 13.2B These three plants came from the wild mustard plant
through artificial selection
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(cabbage, brussel sprouts, kohlrabi): Courtesy W. Atlee Burpee Company; (wild mustard): © Medioimages/Punchstock
Chinese cabbage Brussels sprouts
Wild mustard
Kohlrabi

12. Darwin formulated natural selection as a
mechanism for evolution
 Thomas Malthus who had proposed that death
and famine are inevitable because the human
population tends to increase faster than the
supply of food
 Darwin hypothesized there is a constant struggle for
existence, and only certain members of a population
survive and reproduce in each generation
 Those members that have some advantage are best
able to compete successfully for limited resources
13-12

13.  Darwin called the process by which organisms
with an advantage reproduce more than others
of their kind natural selection
 Some aspect of the environment acts as a
selective agent and chooses the members of
the population with the advantageous phenotype
to reproduce more than the other members
13-13

14.  Essential components of Natural Selection
 The members of a population have inheritable
variations
 A population is able to produce more offspring than
the environment can support
 Only certain members of the population survive and
reproduce
 Natural selection results in a population adapted to
the local environment
 Evolution
 Changes in a population over time due to the
accumulation of inherited differences
13-14

15. 13-15
FIGURE 13.3 The brightly colored tree frog can hide among tropical
plants where the large red eyes confuse predators. The frog climbs
trees and other plants assisted by toes with suction cups

16. 13.4 Wallace independently formulated a
natural selection hypothesis
 Alfred Russel Wallace (1823–1913) was also a
British naturalist
 Wallace’s travels took him to the Amazon and Malay
Archipeligo
 He too had read Malthus’s essay, and in 1858 had the
idea of “survival of the fittest” as well
 Darwin suggested that Wallace’s paper be
published immediately
 Lyell and others suggested that a joint paper be read
to the Linnean Society
13-16

17. HOW SCIENCE PROGRESSES
13A Natural selection can be witnessed
 Darwin formed his idea of natural selection by
observing tortoises and finches on the
Galápagos Islands
 Example: Finches
 Heavy beak of large, ground-dwelling finch suited to seeds
 Beak of warbler-finch suited to feeding on insects
 Longer, de-curved beak and split tongue of cactus-finch
suited for probing cactus flowers for nectar
 Peter and Rosemary Grant are actually watching
natural selection as it occurs in the finches
13-17

18. 13-18
Figure 13A.1 Finches on the Galápagos Islands
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A ground-dwelling finch
feeds on seeds.
A cactus-finch probes flowers
for nectar.
A warbber-finch feeds on insects.
(ground finch, cactus finch): © Laura L. Fellows; (warbler finch): © Greg W. Lasley

19. 13-19
Figure 13A.2 The beak depth of a ground finch varies from
generation to generation, according to the weather
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
dry year dry year dry year
wet year
1984198219801977
BeakDepth
medium
ground finch

20. 13-20
The Evidence for Evolution Is Strong

21. 13.5 Fossils provide a
record of the past
 Best evidence for evolution comes from fossils
 Traces of past life, such as trails, footprints, burrows,
worm casts, or preserved droppings
 Sedimentation
 Weathering and erosion of rocks produces an
accumulation of particles that vary in size and nature
 Sediment becomes a stratum, a recognizable layer in
several layers
 Fossil record
 History of life recorded by fossils and the most direct
evidence we have that evolution has occurred
13-21

22. 13-22
Figure 13.5A
a. Paleontologists carefully remove and study fossils
b. The deeper the stratum, the older are the fossils found there

23. 13-23
Figure 13.5B Fossils are carefully cleaned, and organisms
are reconstructed

24. 13.6 Fossils are evidence for
common descent
 Darwin used the phrase “descent with
modification” to explain evolution
 You and your cousins have a common ancestor in
your grandparents, so one couple can give rise to
many descendants
 Transitional fossil is either the common
ancestor for the two different groups or is closely
related to the common ancestor
 Allow us to trace the descent of organisms
 Ex: Archaeopteryx lithographica
13-24

25. 13-25
Figure 13.6A Fossil of
Archaeopteryx and an artist’s
representation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(fossil): © Jason Edwards/Getty RF; (art): © Joe Tucciarone
reptile characteristics
bird characteristics
wing
wing
tail
feet
head
claws
teeth
feathers
tail with vertebrae
Archaeopteryx fossil

26. 13-26
Figure 13.6B Ambulocetus natans, an ancestor of the
modern toothed whale, and its fossil remains

27. 13.7 Anatomic evidence
supports common descent
 Anatomic similarities exist between fossils and
between living organisms
 Homologous structures – those that are
anatomically similar because they are inherited from a
recent common ancestor
 Analogous structures – those that serve the same
function, but they are not constructed similarly, nor do
they share a recent common ancestry
13-27

28. 13.7 Anatomic evidence
supports common descent
 Comparative anatomy
 Vertebrate forelimbs are used for flight, orientation
during swimming, running, climbing, or swinging from
tree branches
 Yet all vertebrate forelimbs contain the same sets of
bones organized in similar ways despite their
dissimilar functions
 Vestigial structures
 Fully developed in one group of organisms but
reduced and possibly nonfunctional in similar groups
 Pelvic girdle in whales and snakes
13-28

29. 13-29
Figure 13.7A
Despite differences in
function, vertebrate
forelimbs have the
same bones
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whale cat horse human
bat
bird humerus
ulna
radius
metacarpals
phalanges

30. 13.7 Anatomic evidence
supports common descent
 Embryological evidence
 Homology shared by vertebrates extends to their
embryologic development
 At some time during development, all vertebrates
have a postanal tail and paired pharyngeal pouches
 Terrestrial vertebrates can trace their ancestry to
amphibians and then to fishes
13-30

31. 13-31
Figure 13.7B
Vertebrate embryos
have features in
common, despite
different appearances
as adults
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(both): © Carolina Biological Supply/Phototake
Pig embryo
Chick embryo
postanal
tail
pharyngeal
pouches

32. 13.8 Biogeographic evidence
supports common descent
 Biogeography is the study of the distribution of
plants and animals in different places throughout
the world
 Such distributions are consistent with the hypothesis
that life-forms evolved in a particular locale
 Example: Both cactuses and euphorbia are succulent,
spiny, flowering plants adapted to a hot, dry
environment, but cactuses grow in North American
deserts and euphorbia grow in African deserts
 It seems they just happened to evolve on their respective
continents
13-32

33. 13.9 Molecular evidence
supports common descent
 Almost all organisms use the same basic
biochemical molecules, including DNA, ATP,
and many enzymes
 All organisms use the same DNA triplet code and the
same 20 amino acids in their proteins
 Humans share a large number of genes with much
simpler organisms
 Life’s vast diversity has come about by only a slight
difference in the regulation of genes
13-33

34. 13-34
Figure 13.9 Biochemical
differences indicate
degrees of relatedness
among organisms
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18
turtle
Species
0 5 10 15 20 25 30 35 40 45 50 55
51
yeast
30
moth
20
fish
11
duck
9
monkey
2
60
pig
Cytochrome c is a small protein
that plays an important role in
the electron transport chain
within mitochondria of all cells.
Number of amino acid differences
compared to human cytochrome c.

35. 13-35
Population Genetics Tells Us When
Microevolution Occurs

36. 13.10 The human population
is diverse
 Population
 Members of a single species occupying a particular
area at the same time
 All humans are the same species
 Much of the genomic diversity of humans is due to
microvariations such as single nucleotide
polymorphisms (differences) or SNPs
 Humans inherit patterns of base-pair differences now
called haplotypes
13-36

37. 13-37
FIGURE 13.10 The HapMap project compares DNA sequences
among African, Asian, and European populations
to discover unique base-pair differences

38. A Hardy-Weinberg equilibrium is not expected
 Gene pool of a population is composed of all
the alleles in all the individuals making up the
population
 When the allele frequencies for a population
change, microevolution has occurred
 Peppered moth example
13-38
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genotypes
0.04
0.04 + 0.16 0.16 + 0.64
0.20 D 0.80 d
0.32 0.64
DD Dd dd
frequency of genotypes
in the population
frequency of alleles and
gametes in the population

39. 13-39Figure 13.11 Calculating gene pool frequencies for F1 and F2
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eggs
sperm
Offspring
0.20 D 0.80 d
0.20
D
0.80
d
DD
0.04 DD 0.16 Dd
0.16 Dd 0.64 dd
Genotypes:
0.04
D = 0.20 d = 0.80
0.32 0.64
= 0.04
= 0.32
= 0.64
1.00
Genotype frequencies: 0.04 DD + 0.32 Dd + 0.64 dd = 1
Dd dd
F1 generation
Genotype frequencies:
Allele and gamete frequencies:
F2 generation
p2
+ 2pq + q 2 = 1
p2
= frequency of DD genotype (dark-colored) = (0.20)2
2pq = frequency of Dd genotype (dark-colored) = 2(0.20)(0.80)
q2
= frequency of dd genotype (light-colored) = (0.80)2

40. The Hardy-Weinberg Principle
 Potential constancy, or equilibrium state, of gene
pool frequencies was independently recognized
by G. H. Hardy and W. Weinberg
 Binomial equation (p2 + 2pq + q2 = 1) to
calculate the genotype and allele frequencies of
a population
 Formulated Hardy-Weinberg principle
13-40

41.  5 conditions for Hardy-Weinberg
equilibrium
1. No mutations
2. No gene flow
3. Random mating
4. No genetic drift
5. No natural selection
13-41

42. Mutations & sexual recombination produce
variations
 Mutations – permanent genetic changes
 Without mutations, there could be no inheritable
phenotypic variations
13-42

43.  Mutations are the primary source of
genetic differences among asexual
prokaryotes
 In sexually reproducing organisms, sexual
recombination is as important as mutation
in creating phenotypic differences
 Sexual recombination creates new
combinations of alleles
13-43

44.  Nonrandom mating occurs when only certain
genotypes or phenotypes mate with one another
 Gene flow (gene migration) – the movement of
alleles between populations
 Continued gene flow tends to make the gene pools
similar and reduce the possibility of allele frequency
differences between populations
13-44

45. 13-45
Figure 13.13A The anatomy of
the garden pea (Pisum sativum)
ensures self-pollination and
nonrandom mating
Figure 13.13B Occasional cross-
pollination between a population of
Pisum sativum and a population of
Pisum arvense is an example of
gene flow
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Pisum sativam
stamen
stigma
self-
pollination
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Pisum sativum
Pisum arvense
gene flow

46. 13.14 The effects of genetic drift
are unpredictable
 Genetic drift – changes in the allele
frequencies of a gene pool due to chance
rather than selection by the environment
 2 mechanisms
1. Bottleneck effect
2. Founder effect
13-46

47.  Small Versus Large Populations
 Although genetic drift occurs in populations of all
sizes, a smaller population is more likely to show the
effects of drift
 Bottleneck and Founder Effects
 Bottleneck effect prevents the majority of genotypes
from participating in the next generation
 Founder effect is an example of genetic drift in which
rare alleles, or combinations of alleles, occur at a
higher frequency in a population isolated from the
general population
13-47

48. 13-48
Figure 13.14A Chance events can cause allele frequency
changes and genetic drift
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10% of
population
20% of
population
natural disaster kills
five green frogs

49. 13-49
Figure 13.14B A rare form of dwarfism that is linked to polydactylism is
seen among the Amish in Pennsylvania (1/1,000 in general population,
1/14 in Amish community)

50. 13.15 Natural selection can be
stabilizing, directional, or disruptive
 Stabilizing selection
 Occurs when an intermediate phenotype is favored
 Improves adaptation of the population to those
aspects of the environment that remain constant
13-50
Figure 13.15B Stabilizing
selection as exemplified by
human birth weight
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PercentofBirthsinPopulation
PercentInfantMortality
20
15
10
5
10
20
30
50
70
100
5
7
3
2
2 3 4 5 6 7 8 9 10
Birth Weight (in pounds)

51. Figure 13.15C Directional selection in guppies
 Directional selection
 Occurs when an extreme phenotype is favored, and
the distribution curve shifts in that direction
 Such a shift can occur when a population is adapting
to a changing environment
13-51
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(a): © Helen Rodd
AmountofColor
Low
predation
No
predation
High
predation
0 1284
Months
a. Experimental site b. Result
All guppies
are drab
and small
above waterfall
below waterfall

52.  Disruptive selection
 Two or more extreme phenotypes are favored over
any intermediate phenotype
13-52
Figure 13.15D Disruptive selection in snails
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Forested
areas
Low-lying
vegetation
© Bob Evans/Peter Arnold/Photolibrary

53. 13-53
Figure 13.15A Phenotype ranges before and after three types of selection
Blue represents favored phenotype(s)
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NumberofIndividualsNumberofIndividuals
a. stabilizing selection
Peak narrows.
c. disruptive selection
Two peaks result.
b. directional selection
Peak shifts.
Phenotype Range Phenotype Range
Phenotype Range Phenotype Range Phenotype Range
Phenotype Range

54. 13.16 Stabilizing selection can
help maintain the heterozygote
 Variations are maintained in a population for any
number of reasons
 Mutations, gene flow, genetic drift and disruptive
selection can maintain or increase variations in a
population
 Cystic Fibrosis
 Recessive allele codes for defective membrane
protein
 Northwestern European descent
 Typhoid fever agent can use normal version of this
protein, but not the defective one to enter cells
 Heterozygote superiority
13-54

55.  Sickle-Cell Disease
 Condition due to abnormal form of hemoglobin (Hb)
 People who are heterozygous (HbA
HbS
) have an
advantage because they don’t die from sickle-cell
disease and they don’t die from malaria
 Frequency of the HbS
allele is declining among African
Americans because the heterozygote has no
particular advantage in US with low to no malaria
13-55

56. 13-56
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Genotype Phenotype Result
Normal
Sickle-cell trait
Dies due to
malarial infection
Lives due to
protection from both
Dies due to
sickle-cell disease
Sickle-cell
disease
HbA
HbA
HbA
Hbs
Hbs
Hbs

57. 13-57
Figure 13.16 Sickle-cell disease is more prevalent in areas of Africa
where malaria is more common
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
sickle-cell
overlap of both
malaria

58. Connecting the Concepts:
Chapter 13
 Darwin developed theory of natural selection
based on his own observations and the work of
others
 Evolution explains the unity and diversity of life
 Life is unified because of common descent, and it is
diverse because of adaptations to particular
environments
 Application of principles of genetics to evolution
 Hardy-Weinberg equilibrium
 Natural selection is the only agent of evolution that
results in adaptation to the environment
13-58