R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
CHAPTER 7
EVOLUTION—THE THEORY AND
ITS SUPPORTING EVIDENCE
OUTLINE
INTRODUCTION
EVOLUTION: WHAT DOES IT MEAN?
Jean-Baptiste de Lamarck and His Ideas on Evolution
The Contributions of Charles Darwin and Alfred Wallace
Natural Selection—What is Its Significance?
PERSPECTIVE The Tragic Lysenko Affair
MENDEL AND THE BIRTH OF GENETICS
Mendel’s Experiments
Genes and Chromosomes
THE MODERN VIEW OF EVOLUTION
What Brings About Variation?
Speciation and the Rate of Evolution
Divergent, Convergent, and Parallel Evolution
Microevolution and Macroevolution
Cladistics and Cladograms
Mosaic Evolution and Evolutionary Trends
Extinctions
WHAT KINDS OF EVIDENCE SUPPORT EVOLUTIONARY THEORY?
Classification—A Nested Pattern of Similarities
How Does Biological Evidence Support Evolution?
Fossils: What Do We Learn from Them?
Missing Links—Are They Really Missing?
The Evidence—A Summary
SUMMARY
CHAPTER OBJECTIVES
The following content objectives are presented in Chapter 7:
 The central claim of the theory of evolution is that today’s organisms descended, with
modification, from ancestors that lived in the past.
 Jean-Baptiste de Lamarck in 1809 proposed the first widely accepted mechanism—
inheritance of acquired characteristics—to account for evolution.
 In 1859, Charles Darwin and Alfred Wallace simultaneously published their views on
evolution and proposed natural selection as a mechanism to bring about change.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
 Experiments carried out by Gregor Mendel during the 1860s demonstrated that
variations in populations are maintained rather than blended during inheritance, as
previously thought.
 In the modern view of evolution, variation is accounted for mostly by sexual
reproduction and by mutations in sex cells.
 The fossil record provides many examples of macroevolution—that is, changes that
result in the origin of new species, genera, and so on—but these changes are simply
the cumulative effect of microevolution, which involves changes within a species.
 Fossils showing the transition from ancestor to descendant groups, as in fish to
amphibians and reptiles to mammals, are well known.
 A number of evolutionary trends, such as size increase or changing configuration of
shells, teeth, or limbs, are well known for organisms for which sufficient fossil
material is available.
 The theory of evolution is truly scientific, because we can think of observations or
experiments that would support it or render it incorrect.
 Fossils are important as evidence for evolution, but additional evidence comes from
classification, biochemistry, molecular biology, genetics, and geographic distribution.
LEARNING OBJECTIVES
To exhibit mastery of this chapter, students should be able to demonstrate comprehension
of the following:
 the central claim and historical development of the theory of evolution
 Darwin's and Wallace's theory of natural selection as a mechanism for evolution
 Mendel’s concept of inheritance
 variation sources within populations as well as natural selection’s effects on variation
 the models for speciation
 the modern view of evolution, including rates of evolutionary change
 the types of evolutionary trends
 the use of cladograms, and the insight into evolutionary relationships between groups
of organisms that is provided by cladistics
 the evidence for evolution provided by classification, modern biological studies, and
the fossil record
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
CHAPTER SUMMARY
1. Darwin’s observations on the Galapagos Islands provided him with the raw data
that eventually led to the theory of evolution. The central claim of the theory of
evolution is that all organisms have descended with modification from ancestors
that lived during the past.
Figure 7.1
The Galapagos Islands
Figure 7.2
Charles Robert Darwin in 1840
Figure 7.3
Darwin’s Finches of the Galapagos Islands
2. The idea of evolution is not new, but the first widely accepted mechanism to
account for evolution—inheritance of acquired characteristics—was proposed in
1809 by Jean-Baptiste de Lamarck.
3. Charles Darwin’s observations of variation in populations and artificial selection, as
well as his reading of Thomas Malthus’ essay on population, helped him formulate
his idea of natural selection as a mechanism for evolution.
Figure 7.4
Artificial Selection
4. In 1859 Charles Darwin and Alfred Wallace published their ideas of natural
selection, which hold that in populations of organisms, some have favorable traits
that make it more likely that they will survive and reproduce and pass on these
variations.
Enrichment Topic 1. Alfred Russel Wallace
Although students may have heard that Wallace independently developed a theory of
evolution by natural selection, most do not know about the life of the “other”
evolutionist. As a young naturalist, Wallace did fieldwork in the Malay Archipelago in
the late 1850s and early 1860s. He described two great faunal regions separated by a
deepwater gap. Whereas marsupials dominated to the east, carnivores and primates
dominated to the west. This line still bears his name. He was also a prolific collector, a
“ruthless harvester of natural wonders.” Read more about Alfred Wallace in National
Geographic, 214(6), 113-131.
5. Natural selection holds that (a) organisms in all populations possess heritable
variations; (b) some variations are more favorable than others; (c) not all young
survive; and (d) those with favorable variations are more likely to survive and pass
on their favorable variations.
6. Gregor Mendel’s breeding experiments with garden peas provided some of the
answers regarding variation and how it is maintained in populations. Mendel’s
work is the basis for present-day genetics.
Figure 7.5
Mendel's Experiments with Flower Color
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
7. Genes that are specific segments of chromosomes are the hereditary units in all
organisms. Only the genes in sex cells are inheritable. Meiosis yields cells with only
one half the chromosome number of the parent cell—the sex cells. After
fertilization, the fertilized egg develops via a different type of cell division, mitosis.
Figure 7.6
The Double-Stranded, Helical DNA Molecule
Figure 7.7
Meiosis and Mitosis
8. Sexual reproduction and mutations, changes in chromosomes or genes, account for
most variation in populations.
Enrichment Topic 2. How Genetic Engineering Can Further Evolution
Evolution via natural selection operates without consideration of an outcome. Some
variations are favorable, and others are not. However, genetic engineering proceeds with
an end goal in mind. Should technology be used to cure diseases, and alter the
responsible genes so that harmful, disease-causing mutations cannot be passed to the next
generation? Should parents be able to genetically engineer their future child with respect
to physical appearance? There are numerous current sources of information, many on the
Internet, about genetic engineering—including scientific, philosophical, religious, and
political points of view.
9. Evolution by natural selection is a two-step process. First, variation must exist or
arise and be maintained in interbreeding populations, and second, favorable
variants must be selected for survival so that they reproduce.
10. Many species evolve by allopatric speciation, which involves isolation of a small
population from its parent population that is then subjected to different selection
pressures.
Figure 7.8
Allopatric Speciation
Figure 7.9
Speciation in Songbirds
Enrichment Topic 3. Adaptive Radiation of Darwin’s Finches
Peter and Rosemary Grant have been studying Darwin’s finches in the Galapagos for
more than 30 years, far longer than Darwin! They have identified 14 or 15 species that
evolved from the same common ancestor, a seed eater from South America. While
Darwin’s finches present a beautiful example of adaptive radiation, the model is not one
of a tree that branches out into smaller and smaller branches and twigs. In this instance,
the tree is lopsided, with the main trunk splitting into three main branches, only one of
which breaks into several branches and many twigs. The other trunk produces only some
thin twigs. For the adaptive radiation of Darwin’s finches, the Grants describe a model of
allopatric speciation, in which a small population separates from the main population (in
this case by colonizing a new island) and evolves to meet the demands of its new
environment, eventually to become a new species. If the two species later come into
contact, they may coexist if they have diverged sufficiently and are not in competition.
American Scientist, March-April 2002 v.90 n.2 p.130.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
11. When diverse species arise from a common ancestor, it is called divergent
evolution. The development of similar adaptive features in different groups of
organisms results from convergent evolution and parallel evolution.
Figure 7.10
Figure 7.11
Divergent Evolution
Convergent and Parallel Evolution
12. Microevolution involves changes within a species, whereas macroevolution
encompasses all changes above the species level. Macroevolution is simply the
outcome of microevolution over time.
13. Scientists have traditionally used phylogenetic trees to depict evolutionary
relationships, but now they more commonly use cladistic analyses and cladograms
to show these relationships.
Figure 7.12
Phylogenetic Tree and Cladogram
Figure 7.13
Cladograms for Dogs, Birds, and Bats
14. Mosaic evolution means that organisms have recently evolved characteristics as
well as some features of their ancestral group. Size increase is a common
evolutionary trend, but trends are usually complex and subject to reversal.
Evolutionary trends are a series of adaptations to a changing environment or
adaptations that occur in response to exploitation of new habitats. Some organisms,
however, show little evidence of any evolutionary trends for long periods.
Figure 7.14
Evolutionary Trends in Titanotheres
Figure 7.15
Two Examples of So-Called Living Fossils
15. Background extinction occurs continually, but several mass extinctions have also
taken place, during which Earth’s biotic diversity has been decreased markedly.
16. The theory of evolution is truly scientific because we can think ob observations that
would falsify it, that is prove it wrong.
Table 7.1
Some Predictions from the Theory of Evolution
17. Much of the evidence supporting evolutionary theory comes from classification,
comparative anatomy, embryology, genetics, biochemistry, molecular biology, and
present-day examples of microevolution.
Table 7.2
Expanded Linnaen Classification Scheme
Figure 7.16
Classification of Organisms Based on Shared
Characteristics
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
18. Studies in biochemistry provide evidence for evolutionary relationships.
Homologous structures are variations in organs derived from a common ancestor.
Conversely, analogous structures serve a common function, but are dissimilar in
structure and development. Vestigial structures are remnants of structures that were
fully functional in ancestors but serve no function or a reduced function in modern
organisms.
Figure 7.17
Homologous Structures
Figure 7.18
Analogous Structures
Figure 7.19
Vestigial Structures
Enrichment Topic 4. Vestigial Structures in Humans?
Are there vestigial structures in humans? Scientists consider the small muscles around the
ear, as well as the coccyx (tail bone), vestigial structures that are no longer necessary in
modern humans. Students can investigate other proposed vestigial structures (including
the appendix, wisdom teeth), and determine whether features are actual vestigial
structures. Although more than 100 vestigial structures were once proposed for Homo
sapiens, scientists have discerned uses for these once-proposed “useless” features.
19. The fossil record also provides evidence for evolution in that it shows a sequence
of different groups appearing through time, and some fossils show features we
would expect in the ancestors of birds, mammals, horses, whales, and so on.
Figure 7.20 The Fossil Record and Evolution
Figure 7.21 Cladogram Showing the Relationships among Horses,
Rhinoceroses, and Tapirs (Order Perissodactyla)
LECTURE SUGGESTIONS
Evolution as a Theory via the Mechanism of Natural Selection
1. Briefly review “What Kinds of Evidence Support Evolutionary Theory?" (p. 145150) and place it in the context of the scientific method. Emphasize that a theory in
science is a hypothesis that has withstood repeated testing and, as such, is a
powerful tool that offers a good explanation, and is predictive. It has a very
different connotation that our common, everyday use of the word “theory” or
“theoretical.”
2. It is important to provide beginning students (particularly non-majors) with
adequate information concerning the vast amount of accumulated evidence in favor
of modern evolutionary theory. However, most students acknowledge evolution, at
least on some basic level.
A. Ask students if any are involved in breeding animals. Ask these
students and the class in general what procedure you should follow if
you have a champion German Shepherd and wish to make money
breeding your dog and selling the puppies.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
When students acknowledge that a championship dog results from
favorable characteristics from both parents (and not from a champion dog
and a mutt on the street!), question why favorable genes from both parents
are required. If organisms do not change, would it be important to search
for a favorable mate for your dog?
B. Ask students to think of special features of animals (a giraffe’s long neck,
a shark’s streamlined form, camouflage in some moths), and how these
features imparted an evolutionary advantage to the species.
C. Note that the DNA testing techniques that are used to establish
evolutionary relationships among different organisms are also used to
determine whether an individual’s DNA is at a crime scene. Are DNA
techniques effective in the criminal court system? Is it possible that DNA
techniques would not be effective when establishing relationships among
organisms?
D. It may be necessary to emphasize that natural selection and evolutionary
theory make no mention of a higher power or a spiritual realm. (The
theory does not rely on—nor does it deny—the existence of a higher
power.) Emphasize that evolutionary theory is science where religious
beliefs are not scientific because they rely on faith and cannot be tested.
3. Prepared skeletons of various vertebrates (e.g., salamander, frog, cat, bird, and
human) can be used to demonstrate homologies.
4. Some well-studied fossils suites such as the horse or ammonoids can be used to
illustrate how stratigraphic and paleontological studies support evolution.
5. Have students identify and design a “mystery organism” based upon a given set of
parameters. For example, students are told that there is an unseen pollinator of a
giant flower in the rainforest. The flower is 50 cm long from the flower opening to
the location of the pollen—in a very curved, very narrow flower. Students can
design an insect “mystery pollinator.” Change the flower’s parameters, or ask
students to redesign the pollinator as a bird, or a mammal. What are the important
features that the organism must possess in order to reach the pollen? Do any
students’ designs mimic convergent evolution?
6. Within the parameters of scientific theory, students can investigate why
“creationism” and “intelligent design” are not acceptable topics within science
classrooms. It is not possible to design experiments to support or disprove a
spiritual realm.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
CONSIDER THIS
1. Discuss the difference between a scientific theory and a belief, with an emphasis on
the origin and evolution of life. How are they different from each other?
2. What is some of the abundant evidence against the mechanism of acquired
characteristics? For example, what if a baby is born to parents who originally had
large noses before plastic surgery? Will the baby have a small nose?
3. Is there enough evidence for organic evolution on Earth to make it a respectable
theory?
4. How might Darwin's conclusions about evolution have been different if he had
known about the cellular basis of heredity?
5. How effective do you think mutations would be in a single-celled organism?
IMPORTANT TERMS
allele
allopatric speciation
analogous structure
artificial selection
chromosome
cladistics
cladogram
convergent evolution
deoxyribonucleic acid
divergent evolution
gene
homologous structure
inheritance of acquired
characteristics
living fossil
macroevolution
mass extinction
meiosis
microevolution
mitosis
modern synthesis
mosaic evolution
mutation
natural selection
paleontology
parallel evolution
phyletic gradualism
punctuated equilibrium
species
theory of evolution
vestigial structure
SUGGESTED MEDIA
Videos
1. American Experience: The Monkey Trial, PBS Home Video
2. Evolution (boxed set), WGBH Boston Video
3. Evolution: Darwin’s Dangerous Idea, WGBH Boston Video
4. Evolution: Extinction, WGBH Boston Video
5. Evolution: Evolutionary Arms Race, WGBH Boston Video
6. Evolution: Why Sex?, WGBH Boston
7. NOVA. Cracking the Code of Life, WGBH Boston Video
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
8. Scientific American Frontiers Season X. Voyage to the Galapagos, PBS Home
Video
9. Evolution Through Time, Earth Revealed #11, Annenberg/CPB
10. PaleoWorld: Mysteries of Evolution, The Learning Channel
11. Biography: Charles Darwin: Evolution’s Voice, A & E Video
12. Keys to Scientific Literacy: The Story of Evolution, Hawkhill Video
13. The Shape of Life, National Geographic
14. Earth Time: Evolution and Human Memory, BBC
15. Evolution Video Library (17 video clips), Discovery Channel/FFH&S
16. Why Humans Have Legs: The Missing Link, BBCW
17. Galapagos: The Islands that Changed the World, BBC
18. Judgment Day: Intelligent Design on Trial, NOVA, WGBH Boston
19. Natural Selection, VEA
Software and Demonstration Aids
1. Natural Selection, EME Corporation
2. Mendelian Inheritance, slide set, Educational Images, Ltd.
3. The Origins of Life, slide set, Educational Images, Ltd.
CHAPTER 7 – ANSWERS TO QUESTIONS IN TEXT
Multiple Choice Review Questions
1.
2.
3.
4.
b
c
e
c
5.
6.
7.
8.
a
d
e
a
9. c
10. b
Short Answer Essay Review Questions
11. In natural selection, the better an organism is adapted to its environment, the longer
it will survive and the more offspring it will produce relative to other members of
its species. Fitness is measured, not in terms of how big or strong you are, but how
well you elude danger and prosper. So if you’re a small mammal, it’s good to be
well camouflaged and able to build a good burrow. If you’re a lion, a good roar and
sharp claws will serve you well.
12. In allopatric speciation, new species arise when a small part of a population is
isolated from the larger gene pool by some kind of barrier. Isolation may result
from a marine transgression that effectively separates a once-interbreeding species.
Another example would be if land animals are rafted from one area to another
across open water.
13. A vestigial structure is a remnant structure that was fully functional in an ancestor.
The vestigial structure need not be totally functionless, but can have a reduced
function. Examples include dogs’ dewclaws, whales and some snakes’ pelvis
bones.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
14. In divergent evolution, an ancestral species gives rise to diverse descendants
adapted to various aspects of the environment. An example would be an ancestral
mammal of the Late Mesozoic that gave rise to platypuses, armadillos, rodents,
bats, primates, whales, and rhinoceroses. In convergent evolution, similar
characteristics develop in distantly related evolution. An example would be the
similarities of the mammals of North and South America which developed
independently.
15. In punctuated equilibrium, species are stable for extended time periods, and then
evolution occurs rapidly, giving rise to a new species. Proponents of punctuated
equilibrium argue that there are few examples of gradual transition in the fossil
record. In phyletic gradualism, gradual accumulation of minor changes eventually
brings about the origin of a new species. Phyletic gradualism does appear in the
fossil record as well (horse, ammonoids).
16. See Table 7.1. If evolution has taken place, the oldest fossil-bearing rocks should
have remains of organisms very different from those existing now, and more recent
rocks should have fossils more similar to today’s organisms. If today’s organisms
descended with modification from ones in the past, there should be fossils showing
characteristics connecting orders, classes, and so on. If evolution is true, closely
related species should be similar not only in details of their anatomy, but also in
their biochemistry, genetics, and embryonic development, whereas distantly related
species should show fewer similarities.
17. Macroevolution involves changes such as the origin of a new species, or the origin
of new genera, families, orders, and classes. Good examples would include the
origin of birds from reptiles, the origin of mammals from mammal-like reptiles,
and the evolution of whales from land-dwelling ancestors.
18. Students will produce a variety of cladograms. The best-drawn cladograms will
exhibit patterns based on derived characteristics (Sharks do not have a completely
bony skeleton, so their skeleton is more “primitive” than the others. While whales
can swim, they are examples of mammals who returned to the sea; their skeletons
show vestigial structures—pelvis, hind limbs. Bears are mammals, and more
closely related to whales—both have mammary glands, bony skeletons, etc.)
19. Evolution just means change through time, so we would find changes from one
organism to another and we would find terminal extinctions of organisms.
20. Mendel’s experiments showed that the factors (genes) that control traits do not
blend during inheritance, and even though these traits may not be expressed in each
generation, they are not lost. Therefore, some variation in populations is accounted
for by alternate expressions of genes. Mendelian genetics explains much about
heredity and explains the origin of variations in populations, and how variations in
populations are maintained.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
Apply Your Knowledge
1. The group in Congress is operating under the premise of Lamarckian evolution,
which holds that new traits arise in organisms because of their needs. These new
traits could supposedly be passed on to descendants. This mechanism is incorrect,
and has been rejected by the scientific community. Natural selection is the
mechanism for evolution accepted by the scientific community. Variation in
populations is accounted for by genetics and sexual reproduction. Mutations may
arise spontaneously, but only those in sex cells can be passed on to future
generations.
2. If present-day tapirs, horses, and rhinoceroses are more closely related to one
another than they are to any other living hoofed mammal, then as we trace these
animals back through the fossil record, it should become increasingly difficult to
differentiate between them. Also, their anatomies should be similar, as well as their
blood chemistries, and their embryological development.
3. The first statement is irrelevant to theories in general, because the person is not
using the word in the scientific sense. In science, a theory is supported by a
multitude of data, it offers a good explanation for observable phenomena, and it is
predictive. The second statement—that fossils are arranged in a sequence of
density, shape, and habitat—can be refuted with several examples. The fossil record
shows a sequence of the first appearances of various organisms through time, with
one-celled organisms appearing before multicelled organisms, invertebrates
appearing before vertebrates, etc. We can also see in the fossil record that
organisms arising from a common ancestor are more and more similar and difficult
to tell apart as we trace these animals back.
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