CHAPTER 21: THE EVIDENCE FOR EVOLUTION
WHERE DOES IT ALL FIT IN?
Chapter 21 builds on the population genetics information covered in Chapter 20 to provide a
rationale for evolution. Students need to recall gene expression, heredity, and gene distribution to
fully understand the information in this chapter. A complete knowledge of Chapter 21 is essential for
understanding the principles of organic evolution covered in Chapter 22. In addition, any coverage of
organismic diversity and adaptations relies on the concepts expounded in this chapter.
SYNOPSIS
There is solid scientific evidence and it exists in multiple lines of evidence other than just the
fossil record. Many students upon hearing the term “evolution” even though they may be biology
majors feel that this means that humans evolved from apes. Unfortunately, this is only a very
small part of the theory, but because it challenges various religious beliefs, evolution is
frequently rejected as heresy.
His studies of fossils, geological strata, knowledge of artificial selection, plus the five year
voyage on the Beagle helped Darwin to formulate his theory of evolution by natural selection. As
a result of more accurate radioactive dating methods the fossil record today is much more
complete and the strata that contain those fossils can be aged more accurately. The fossil record
for horses is quite complete and clearly shows how they evolved over a long period of time. The
primary physical changes from Hyracotherium to Equus involved increase in body size, toe
reduction, and changes in dentition. In many ways this evolution parallels that of humans, most
notably in the present lack of species diversity. The initial examination of the Galápagos finches
aided Darwin in his development of the theory of evolution by natural selection. Peter and
Rosemary Grant’s conducted a reexamination of several of the species in 1973 and reaffirmed
Darwin’s original work. It further supported the impact that the environment has on the nature
of an organism. Peppered moths and industrial melanism show how natural selection favors new
traits as the environment changes. Coal burning by heavy industry is attributed to causing these
changes by darkening tree surfaces, which resulted in a predominance of dark colored moths.
The white moths stood out against the darker background allowing the birds to selectively forage
on them versus the darker colored moths.
Artificial selection occurs when humans favor certain genetically based phenotypic traits in
plants or animals resulting in the development of new forms. Evolution at this level has occurred
in the laboratory and has been operational through centuries of agricultural development and
domestication. Examining anatomical homology (forelimbs of vertebrates), developmental
processes (similarities of embryo development), imperfect structures (neck vertebrae in giraffes)
and vestigial structures (vermiform appendix in humans) provides further evidence for evolution.
Most recently, the molecular record has provided a wealth of support to help determine
evolutionary relationships among species. One would expect organisms with similar appearance
to have similar expressed DNA. Non-coding regions of junk DNA are equally similar
unequivocally and thus provide strong supporting evidence for evolution. Studies in
biogeography reveal that convergent evolution can result in similar appearing communities that
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are only distantly related. Natural selection actually favors such parallel evolution. The similarity
in the organisms is a result of analogous rather than homologous evolution. A classic example of
convergent evolution is the comparison of placental and marsupial mammal communities
between North America and Australia. Although there is little dissention in the scientific world
with regard to Darwin’s theory of evolution by natural selection, there is still great controversy
among the general public. Darwin’s critics raise seven arguments, all without scientific merit, as
to why evolution should not be taught in schools.
LEARNING OUTCOMES
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Describe of evolutionary information the fossil record provides and how we know that it is
reliable.
Explain how horses evolved from dog-size browsers to present fleet-footed grazers.
Explain why beak size in Darwin’s finches provides a classic example of evolution by natural
selection.
Explain how industrial melanism can shift phenotypes within a population as a result of
natural selection.
Recognize how artificial selection by humans results in evolutionary change.
Understand why studies of homology, development, imperfect structures and vestigial
structures provide important information supporting evolution.
Explain how the molecular record provides evidence for evolution.
Describe and give examples of convergent evolution.
Understand why there is still public controversy regarding the teaching of evolution.
Understand the lines of scientific evidence that support evolution to be able to refute the
arguments why evolution should not be taught in schools.
COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 21 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.
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Students believe that all genes program for visible traits
Students are unfamiliar with the exact nature of regulatory gene in determining traits
Students believe that only the observable phenotype is subject to selection
Students do not fully understand the role of genetic drift in variation
Students believe that vestigial traits disappear over time because of disuse
Students believe that acquired traits are inherited
Student believe evolution is driven to make “better” organisms
Students believe that organisms adapt to change rather than being selected
Students do not take into account mutation in determining population genetics
Students believe selection only kills off weaker individuals
Students believe “fitness” is an absolute set of characteristics
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Students believe that species are genetically distinct and fixed
Students are not familiar with the similarity of embryological development between
different groups of organisms
Student are unaware that plants undergo embryological development
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
Stress that the environment doesn’t cause changes in characteristics of an individual; instead it
causes changes in the species itself. The changing environment opens up new habitats for
individuals possessing different alleles combinations to thrive and be successful which increase
their fitness. Species that are unable to change with the environment will eventually die out due
to decreased fitness. There are advantages to
possessing genes that enable flexibility – being a “jack of all trades” as opposed to being a
specialist. Consider the human types that are most likely to survive catastrophes – those that can
adjust to all circumstances, are inventive, creative, and generally able to make something
workable out of string and sealing wax.
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with the
tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 21.
Application
Analysis
Synthesis
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Have students describe examples of artificial selection at the grocery
store.
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Have students why the body size of coyotes living in urban areas is
smaller than those in the wilderness.
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Ask students to explain how the disappearance of alleles from a
population can lead to speciation.
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Have students explain why mosquitoes do not develop resistance to being
killed by a chemical called DDT.
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Ask students to analyze the role of genetic drift in explaining speciation.
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Ask students to hypothesize about the cockroaches remained virtually
unchanged for millions of years.
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Ask students to explain what conditions must be necessary for humans to
speciate.
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Ask students to explain if a complete reliance on computers to calculate
everyday tasks would lead to populations of people with smaller brains.
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Evaluation
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Ask students to describe how a plant can speciate in one generation
without undergoing changes in chromosome number.
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Ask students debate the value of selective breeding in agricultural
animals.
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Ask students to evaluate the biological consequences of extinctions
caused by human activity in an environment.
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Ask student assess the accuracy of using protein differences to distinguish
the differences and similarities between two related species.
VISUAL RESOURCES
Prepare slides or transparencies showing additional evidence for evolution: fossils,
homologies, vestigial structures (including hip bones in python pelvis), development and so
forth. Pass around during class actual fossils for students to examine while you describe them,
their age, and where they were found around the world. Have a paleontologist visit your class
and present a short lecturer on the fossil record of plants and animals. Introduce students to
some of the writings of Stephen J. Gould, such as “The Panda’s Thumb.”
Bring several different types of onions, carrots, potatoes, tomatoes, squash or apples to class for
discussion of artificial selection.
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. Darwin’s Voyage
Introduction
Misconceptions and a lack of knowledge about Darwin’s voyage on the HMS Beagle are
major hindrances to developing student understanding of evolution. This activity provides a
visual time-line of Darwin’s memorable journey.
Materials
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Computer with live access to Internet
LCD projector attached to computer
Web browser with bookmark for About Darwin Voyage Page at
http://www.aboutdarwin.com/voyage/voyage01.html
Procedure & Inquiry
1. Review the principles of evolution proposed by Darwin.
2. Tell students they will be viewing a history of the Beagle’s voyage.
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3. Go through the history and click on the detailed note pages.
4. Have the class answer questions related to particular parts of the journey and have
students hypothesize on Darwin’s observations as if they were not yet familiar with the
theory of natural selection.
B. Extrapolation Concept Map
Introduction
This fun and fast way to engage students in developing a sense of evolution is to link
evolution to observations seen today. Have the students select relevant examples of natural and
artificial selection in everyday life. The simple click and drag animated concept mapping tool
should be practiced before using in class.
Materials
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Computer with live access to Internet
LCD projector attached to computer
Web browser with bookmark to Michigan State University C-Tool:
http://ctools.msu.edu/ctools/index.html
Chapter outline of book for Chapters 1 through 19 projected on overhead
Procedure & Inquiry
1. Tell students that you would like to do a quick survey of everyday examples of natural
and artificial selection.
2. Then go to the Michigan State University C-Tool and add the concept map terms
“Natural Selection” and “Artificial Selection”. Space out the terms to permit branching.
3. Ask the students to find examples of each. Also ask them to think of any overlapping
examples.
4. Use the “Add” and “Concept Word” feature to place the terms on the map for “Natural
Selection” or “Artificial Selection”.
5. Then ask the students to justify the concept linking lines. Use the “Add” and “Linking
Word” feature to place student comments on the map.
6. Continue the activity until you feel the students made a comprehensive map.
USEFUL INTERNET RESOURCES
1. Artificial selection is a fundamental principle in breeding animals for agriculture. Student
understanding in artificial selection can be reinforced by showing modern applications of
genomic information related to artificial selection of agriculture. The National Institutes
of Health has an informative website demonstrating how artificial selection is used in the
breeding of chickens. The website can be found at
http://www.ncbi.nlm.nih.gov/genome/guide/chicken/.
2. The University of California at Berkeley provides a valuable website on natural selection
called Understanding Evolution. It provides resources that can be shared with students
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that supplement the information covered in Chapter 21. The website is available at
http://evolution.berkeley.edu/evolibrary/home.php.
3. Photographs and stories of Darwin’s observations of birds the Galapagos Islands are ideal
for supplementing a lecture on evolution. Rochester Institute of Technology has a
websites detailing the birds Darwin encountered on the Galapagos Islands. This site is
available at http://www.rit.edu/~rhrsbi/GalapagosPages/DarwinFinch.html.
4. Cases studies are an effective tool for reinforcing the concepts related to population
dynamics. The University of Buffalo provides a teaching case study called “The
Evolution of Creationism: Critically Appraising ‘Intelligent Design’. It encourages
students investigate the ideas behind the evolution and creationism debate. The website is
available at http://www.sciencecases.org/id/id.pdf.
LABORATORY IDEAS
This quick laboratory activity encourages students to artificially select for yeast that live
at alcohol concentrations. Artificial selection with this goal is used to develop yeast that can be
used in the brewing and backing industries.
a. Students should be provided with the following materials to perform this open-ended
experiment on producing yeast that can survive in high glucose environments.
a. Sterile Petri plates containing solid Yeast Growth Media or nutrient agar
supplemented with glucose at 1 g/l
b. Packet of bakers or brewer yeast dissolved in 250 ml of sterile nutrient broth
supplemented with glucose at 1 g/l
c. 100% ethanol
d. Sterile water in screw-top container
e. Sterile test tubes covered with culture caps or cotton
f. Clean graduated cylinders
g. Droppers
h. Sterile 1ml pipettes
i. Microbiology laboratory references
b. Discuss how yeast can be grown in liquid medium and transferred to Petri plates as a way
of counting yeast concentration
c. Ask students to design an experiment to see if they can select for yeast that grow at high
alcohol concentrations
d. Have the students set up the experiment and check the progress of yeast growth over the
term of the experiment.
e. Students should be able to compare yeast grown at various alcohol concentrations to a
control
LEARNING THROUGH SERVICE
Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
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and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
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Have students design do a poster for a library on Darwin’s voyage on the Beagle.
Have students tutor high school students covering natural selection in a biology class.
Have students do a presentation about artificial selection for a FFA or 4H group.
Have design educational materials on the artificial selection of antibiotic resistant
bacterial for distribution in the community.
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