Download II. The Discovery of Evolution

Chapter 2
Genetics and Evolution
Learning Objectives
After studying this material, students should be able to:
1.
Describe the history related to the classification of living things.
2.
Describe the classification system used by Linnaeus and how it differed from other systems.
3.
Describe how taxonomy uses comparisons to classify organisms.
4.
Distinguish between analogies and homologies and provide examples of each.
5.
List the occurrences in Europe that lead to the discovery of evolution.
6.
Describe the basic findings of Darwin that contributed to his theory of evolution.
7.
Describe the basic fundamental unit of heredity.
8.
Describe the process of cell division.
9.
Distinguish between dominance, recessive and co-dominance.
10.
List and define the four evolutionary forces that produce genetic change.
11.
Describe the process of natural selection.
12.
Summarize the case of sickle-cell anemia and describe how it serves as an example of
evolutionary forces at work.
13.
Determine the reasons that studying the evolution of continuous traits is more difficult than the
evolution of a trait controlled by a single gene.
14.
Provide examples of the traits that anthropologists analyzing clines might study.
Lecture Outline
I. The Classification of Living Things
1. The authors begin this chapter by distinguishing the scientific theory of evolution from the
creation stories that are a part of the mythology of all peoples.
2. They then turn to a discussion of the background to and development of evolutionary theory.
Prior to the “Age of Discovery,” Europeans arranged both living things and inanimate objects
into a “Great Chain of Being,” with humans at the top.
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3. In the 18th century, Carl von Linné, or Carolus Linnaeus, classified humans, monkeys, and
apes together as primates, one of several kind of mammal.
4. Linnaeus devised a system of progressively more inclusive categories of living things. The
species is the smallest unit of this system; species are subdivisions of the more inclusive unit,
the genus (plural is genera).
5. Taxonomy, the science of classification, now is based on various types of evidence, including
molecular comparisons. Comparisons across species can help identify analogies—anatomical
features with similar function, and homologies—those features that evolved from a common
ancestral feature.
6. A table illustrates the taxonomic system by showing the classification of humans, pointing out
also that humans are chordates with a notochord running along the back of our body during the
embryonic stage of our life cycle.
7. The text then uses the classification to illustrate how the taxonomy is continually redrawn by
explaining what is included within the groups hominoids, hominids, and hominins.
8. In current usage, the first refers to humans and all apes; the second to humans and their
ancestors, as well as, in some newer formulations, the African apes; the last, now gaining more
use, to humans and their ancestors.
II. The Discovery of Evolution
1. The construction and mining that came with the industrialization of Europe brought with it
the discovery of all sorts of fossils of past life forms.
2. By the beginning of the 19th century, many naturalists had accepted the idea that life had
evolved, but they were unsure of the mechanism.
3. Charles Darwin formulated a theory of that mechanism. Darwin’s observations during the 5year voyage of the HMS Beagle and other observation, reading, and discussion led him to the
theory of natural selection.
4. Alfred Russel Wallace came up with a similar theory at the same time.
5. Other naturalists of the period further expanded the theory.
6. One problem, however, was that Darwin did not understand the mechanism of heredity.
7. The work of Gregor Mendel, being done at about the same time, would have provided this
understanding, but Darwin had not read Mendel’s major paper and Mendel’s work was hardly
known until 1900.
III. Heredity
A. The Transmission of Genes
1. The fundamental unit of heredity is the gene.
2. Mendel deduced the gene’s existence during his work with peas, and worked out several laws
of gene behavior, including the law of segregation and the law of independent assortment.
3. Work in the 20th century established the cellular and molecular basis for these inferences.
4. Chromosomes are the structures in cells that contain genetic information. They are formed of
DNA, a complex molecule whose chemical bases are the recipes for making proteins.
5. They do this in steps. Each codon, or base sequence of a gene, specifies the production of an
amino acid, the building blocks of proteins.
6. The directions for a protein are converted to RNA by transcription.
7. RNA then travels to ribosomes, where translation of the codon’s directions into proteins
occurs.
8. The 20 amino acids are strung together in different amounts and sequences to produce a very
large number of proteins. This is the genetic code, common to all forms of life.
B. Genes and Alleles
1. The text then focuses more narrowly on genes. These units specify production of an enzyme,
or a kind of protein that produces a chemical reaction.
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Genetics and Evolution
2. Genes have alternate forms, or alleles. Blood types are an example.
3. The human genome contains 3 billion bases and about 30,000 functioning genes.
C. Cell Division
1. An organism’s body is maintained as cells divide and produce new cells.
2. To do this, the DNA divides and reforms to constitute a new cell nucleus.
3. This is mitosis and it produces a new cell with exactly the same genes as the parent cell.
4. In sexual reproduction, however, cells divide by meiosis. Here, different types of new cells
are formed.
5. If the original cells were homozygous, with identical alleles, then the new cells will have the
same allele.
6. If they were heterozygous, with different alleles, then the new cell will have one or the other.
7. An individual’s genotype, or genetic composition, results from this process.
8. Heterozygous and homozygous individuals will show the same phenotype, or expressed
physical condition.
9. Some alleles mask another and are dominant, while the other is recessive.
10. Co-dominance is also possible.
11. The A-B-O blood type system provides examples for this discussion, with hemoglobin cited
an example of a protein with over a hundred alleles.
D. Polygenetic Inheritance
1. Many physical traits are determined by more than one gene. This is polygenetic inheritance.
IV. Evolution, Individuals, and Populations
1. Turning from the individual to the group, a key genetic concept is the population, or group
within which breeding takes place.
2. It is within populations that natural selection occurs and evolution, defined as changes in
allele frequencies, takes place.
3. The characteristics of the population should remain stable as its gene pool, or available
genetic variants, remains stable.
4. The Hardy-Weinberg principle algebraically shows how this occurs, provided certain
conditions are met.
5. These conditions, however, are rarely met, so changes occur within the gene pool and
evolution can take place.
V. Evolutionary Forces
1. Mutation
1. Mutation of genes is the ultimate source of evolutionary change.
2. Mutations occur when copying mistakes are made during cell division.
3. These are purely chance events. What happens once they occur depends on actions at the
population level.
2. Genetic Drift
1. Various random events within a population can change the frequencies of gene variants. This
is genetic drift.
2. One kind of genetic drift, the founder effect, occurs when a population splits.
3. Especially if a new population contains a small number of individuals, it is unlikely that its
gene frequencies will be representative of the larger population.
3. Gene Flow
1. Gene flow, the introduction of new alleles from another population also changes a
population’s gene pool.
2. Interbreeding allows this, but can be affected by geographic and social factors.
4. Natural Selection
1. Adaptation is a series of beneficial adjustments to the environment.
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2. Natural selection is the evolutionary process through which genetic variation in a population
is shaped to fit environmental conditions.
3. Selection works on behavioral as well as physical traits.
4. Altruism—concern for the welfare of others—is discussed to show how selection can
promote beneficial cooperative behavior.
5. Natural selection may also promote stability through stabilizing selection.
VI. The Case of Sickle-Cell Anemia
1. A detailed discussion of the well-known case of sickle-cell anemia serves as an example of a
number of these evolutionary forces at work.
VII. Adaptation and Physical Variation
1. Studying continuous traits controlled by multiple genes adapting to a specific environment
can be complex.
2. Anthropologists study diversity in terms of clines, or the continuous gradation in the
frequency of a trait or allele over space.
3. Clinical analysis allows anthropologists to study traits to interpret human global variation in
response to adaptation.
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Genetics and Evolution
Features with Discussion Topics and Homework Assignments
A. Biocultural Connection—The Social Impact of Genetics on Reproduction: The genetics
revolution has raised new questions for the biocultural study of reproduction. Anthropologist Rayna
Rapp has studied amniocentesis in America. Her research has traced the development of this
procedure and illustrated the complex interplay of biological knowledge and cultural practices.
1. Homework assignment: Have students further research the controversy regarding
amniocentesis in America. Have them answer the questions posed in the text: What do you
think about prenatal genetic testing for diseases? Would you like to know if you carry the
recessive allele for a harmful condition? Once they have considered these questions, have
them discuss their findings and opinions in class.
B. Original Study—Jonathan Marks. 98% Alike: What Our Similarity to Apes Tells Us about Our
Understanding of Genetics: Humans and chimpanzees have obvious physical differences, but yet
are over 98 percent alike genetically. Marks examines this paradox, showing how difficult it is to
quantify a three-dimensional anatomical comparison. He then explains how the raw number that
results from the one-dimensional genetic comparison can be misleading, but concludes that the two
patterns (anatomical and genetic) actually are quite close.
1. Homework assignment: As homework have students research the similarities and
differences between humans and chimpanzees. Allow students to determine their method of
reporting this information back to you. Suggestions include report form, poster, drawing,
collage, or other acceptable method.
C. Anthropology Applied- What it Means to Be a Woman: How Women Around the World Cope
with Infertility: This article describes anthropologists who study the social consequences of
infertility throughout the world. In some cultures being infertile causes extreme suffering for
women making it a human-rights issue. As a result researches are working to prevent causes of
infertility, such as reducing the incidence of STDs.
1. Homework assignment: Ask students to compare and contrast world views on the topic of
infertility. Assign members of the class to research different parts of the world and then
report back on their findings. Discuss in class the different views that they discovered.
In-Class Projects and Activities
A. Gummy Bear Genetics: Do an online search for “Gummy Bear Genetics” to download a lesson
plan for investigating Mendelian and non-Mendelian genetics through the use of gummy bear
traits (written by William P. Baker and Cynthia L. Thomas). Students enjoy this activity as it
concretely illustrates these concepts as well as provides a colorful snack.
B. Constructing a Cladogram: This activity addresses one of the most challenging statements
regarding human evolution—“I didn’t come from a monkey”—by having the students compare
and contrast the characteristics of primates and non-primates. For this activity, the instructor will
need to present several samples of animal skulls for the students to compare. Examples may
include: Human, Gorilla, Chimpanzee, Spider Monkey, Cat, Raccoon, Dog, etc. Directions for
this activity can be obtained from the Smithsonian National Museum of Natural History
Anthropology Teaching Resources or via the link:
http://anthropology.si.edu/outreach/Teaching_Activities/pdf/Human%20Evolution%20and%20D
arwin.pdf
C. Beanbag Population Genetics: Another activity from the Smithsonian demonstrates the forces
of mutation, migration, random genetic drift, and natural selection—which all act on populationsby using beans of two different colors. This is a fairly simplistic demonstration that does not take
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into account dominance, linkage, or other complexities of genetics, but its simplicity will give
students an appreciation for how the genetic makeup of a population can be altered over time by
seemingly minor forces. This activity can be obtained via the link:
http://anthropology.si.edu/outreach/Teaching_Activities/edpopula.html
Key Terms
Adaptation (p. 45)
Alleles (p. 35)
Analogies (p. 29)
Chromatid (p. 34)
Chromosomes (p. 33)
Clines (p. 50)
Codon (p. 34)
DNA (p. 34)
Dominance (p. 39)
Enzyme (p. 35)
Evolution (p. 41)
Founder effects (p. 43)
Gene (p. 33)
Gene flow (p. 43)
Gene pool (p. 41)
Genetic code (p. 35)
Genetic drift (p. 43)
Genome (p. 35)
Genotype (p. 38)
Genus (p. 29)
Hardy-Weinberg principle (p. 41)
Hemoglobin (p. 39)
Heterozygous (p. 38)
Homologies (p. 29)
Homozygous (p. 38)
Law of independent assortment (p. 33)
Law of segregation (p. 33)
Mammal (p. 28)
Meiosis (p. 37)
Mitosis (p. 37)
Mutation (p. 42)
Natural selection (p. 32)
Notochord (p. 31)
Phenotype (p. 39)
Polygenetic Inheritance (p. 39)
Population (p. 41)
Primate (p. 28)
Recessive (p. 39)
Reproductive success (p. 46)
Ribosomes (p. 35)
RNA (p. 35)
Sickle-cell anemia (p. 48)
Species (p. 29)
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Genetics and Evolution
Stabilizing selection (p. 47)
Taxonomy (p. 29)
Transcription (p. 35)
Translation (p. 35)
Applying Anthropology
Politics and Science: All search for knowledge takes place in a political context; laboratories may be
“ivory towers,” but they don’t exist in a vacuum. The history of investigation into evolution and genetics
has been particularly tied up with political issues; some examples of this are the role of the church in the
initial reception of Darwin’s thought, the pursuit of Lamarckian notions of inheritance by Soviet
geneticists in the 1930-1960 period, and the current issues surrounding federal funding for the Human
Genome Project in the U.S. Choose one of these or find another example of the interaction of science and
politics to examine.
Genetics and Disease: The textbook examines the genetic basis of sickle-cell anemia in some detail, as it
is particularly instructive for our understanding of human evolution. Choose another disease that appears
to have a genetic basis and prepare a brief research report on it. With what other factors is the disease
connected? How does modern medicine approach its treatment?
Creationism: What are the basic claims of creationists? Why do they feel that creationism can be called
“scientific” and why do most scientists disagree with this formulation? What are the legal issues
surrounding the creation/evolution controversy in the United States? (Some places to start: Did the Devil
Make Darwin Do It? [Iowa State University Press, 1983]; Is God a Creationist? The Religious Case
Against Creation Science [Scribner's, 1983]; Science and Creationism: A View From the National
Academy of Sciences [National Academy Press, 1987]; The Creationists [Knopf, 1992]; Evolution vs.
Creationism: An Introduction [California, 2004].)
Other Resources
Films:
“Creation versus Evolution: Battle in the Classroom” (1982, 58 min.) is a bit out of date but
brings out clearly the different perspectives on the creation/evolution issue.
“Evolution: Learning & Teaching Evolution” (2001, 95 minutes) Seven short segments combine
storytelling and science to explore evolution and spark students' interest. The videos stand alone, or
can be used with the companion teacher's guide. Segment 1- Isn't Evolution Just a Thoery?, Segment
2- Who Was Charles Darwin?, Segment 3- How Do We Know Evolution Happens?, Segment 4- How
Does Evolution Really Work?, Segment 5- Did Humans Evolve?, Segment 6- Why Does Evolution
Matter Now?, Segment 7- Why Is Evolution Controversial Anyway? Teaching Evolution Case
Studies- Four additional segments highlight strategies for teaching evolution, including ways to
address the controversy that can arise. The Evolution project offers a groundbreaking and definitive
view of the extraordinary impact the evolutionary process has had on our understanding of the world
around us. Look for additional Evolution resources-online student lessons, a multimedia library, and
an interactive Web site at www.pbs.org/evolution. The eight-hour Evolution broadcast series is also
available on video.
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“Inherit the Wind” is the classic feature film on the Scopes trial (1960, 127 min.).
For films relating to biological aspects of the study of human evolution, see the heading “Physical
Anthropology” in Films for Anthropological Teaching.
Additional Readings:
Genetics:
Michael R. Cummings, Human Heredity (West, 1994).
Daniel L. Hartl, A Primer on Population Genetics, 3rd ed. (Sinauer, 2000).
Arthur Mange and Elaine Mange, Genetics: Human Aspects, 2nd ed. (Sinauer, 1990).
DNA, Human Genome Project, and Public Policy:
John Gribbin, In Search of the Double Helix (Bantam, 1993).
Daniel J. Kevles and Leroy Hood, eds, The Code of Codes: Scientists and Social Issues in the
Human Genome Project (Harvard, 1992).
Richard Lewontin, Biology as Ideology (Harper Perennial, 1992).
Matt Ridley, Genome: The Autobiography of a Species in 23 Chapters (HarperCollins, 1999).
Val Woodward, Human Heredity and Society (West, 1992).
History of Evolutionary Theory:
E. Janet Browne, Charles Darwin: Voyaging and Charles Darwin: The Power of Place
(Princeton, 1995 and 2002)
Stephen J. Gould, Full House: The Spread of Excellence from Plato to Darwin (Harmony) and
Time’s Arrow, Time’s Cycle: Myth and Metaphor in the Discovery of Geological Time
(Harvard, 1987).
David Young, The Discovery of Evolution (Cambridge, 1992).
Ernst Mayr, The Growth of Biological Thought (Harvard, 1982)
Models:
Check with the Carolina Biological Supply Company (Burlington, NC 27215) for 3-D models of
DNA, cells, and so on. They also have kits that can be used to demonstrate genetic traits such as PTC
tasting.
Complementary Perspectives:
Depending on the student body at your institution, the creation/evolution issue can be an important
one. Like most introductory text books, this one does not devote much coverage to the issue. If this
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Genetics and Evolution
question is likely to be a personal one for your students, discussion of the concept of cognitive
dissonance can be helpful at this point in recognizing the conflicts that some may be experiencing.
Likewise, providing students with a bibliography of books on the creation/evolution controversy at
your library can allay the suspicion that you are simply being one-sided. Campus and local clergy
from Judaic, Christian, and Islamic communities can also be helpful.
The intellectual history of the idea of evolution can place it in a useful perspective. Ideas of the
“Great Chain of Being,” Enlightenment notions of progress, and evolutionary ideas in the realm of
social thought accompanied and impacted the rise of evolutionism in biology. The fact that Darwin,
Mendel, Linnaeus and others were working in different spheres but nevertheless came up with highly
complementary ideas speaks persuasively to the reality of evolutionary change, now also backed up
by advances in biochemistry.
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