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CHAPTER 1
Science of Zoology
and
Evolution of Animal Diversity
CHAPTER OUTLINE
1.1
1.2
A Legacy of Change
A. Major feature of life’s history is a legacy of perpetual change.
1. Fossil record is imperfect, but records the broken history of evolution.
2. Organic evolution is the major feature of life.
B. Theory of perpetual change is evolution.
1. Zoology is the scientific study of animals.
2. Life’s multicellular animal history began more than 540 million years ago.
3. Phylogeny is the branching sequence of evolution.
4. Newly formed species gain their characteristics and modifications from previous species.
5. Two major goals: 1) Reconstruct phylogeny of animal life, and 2) Understand historical processes
that generate and maintain diverse species and adaptations throughout evolutionary history.
6. Significant steps in evolutionary origins include multicellularity, a coelom, spiral cleavage,
vertebra, and homeothermy.
A. Principles of Science
1. Science is a way of asking about the natural world to obtain precise answers.
2. On Jan 5,1982, Judge Overton prohibited Arkansas from enforcing Act 590.
3. Science is separate from activities such as art and religion.
4. The trial over creation science provided a definition of science.
a. Science is guided by natural law.
b. Science has to be explanatory by reference to natural law.
c. Science is testable against the observable world.
d. Science conclusions are tentative; they are not necessarily the final word.
e. Science is falsifiable.
5. Science is neutral regarding religion and does not favor one religious position over another.
B. Scientific Method
1. Criteria for science form a hypothetico-deductive method.
2. Hypotheses are based on prior observations of nature or derived from theories based on nature.
3. Testable predictions are made based on hypotheses.
4. A hypothesis powerful in explaining a wide variety of related phenomena becomes a theory.
5. The null hypothesis cannot be proved correct.
6. The most useful theories explain the largest array of different natural phenomena.
7. Scientific meaning of “theory” is not the same as common usage of theory as “mere speculation.”
C. Experimental Versus Comparative Methods
1. Questions can be divided into those that seek to understand proximate versus ultimate causes.
2. Studies that explore proximate causes are experimental sciences using experimental methods
that:
a. Predict how a system being studied will respond to disturbance or treatment,
b. Make the disturbance, and then
c. Compare the observed results with predicted ones.
3. Controls are repetitions of an experiment that lack disturbance or treatment.
4. The sub-fields of molecular biology, cell biology, endocrinology, immunology, physiology,
developmental biology and community ecology rely heavily on experimental scientific methods.
5. Ultimate causes are addressed by questions involving long-term time spans.
a. Comparative Methods are used to address ultimate causes.
b. Patterns of modern similarities are used to establish hypotheses on evolutionary origins.
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c.
1.3
Sub-fields include comparative methods in the following areas: comparative biochemistry,
molecular evolution, comparative cell biology, comparative anatomy, comparative physiology
and behavior, and phylogenetic systematics.
Origins of Darwinian Evolutionary Theory (Figure 1.3)
A. Darwin’s theory helps us understand both the genetics of populations and long term trends in the fossil
record.
B. Darwin and Wallace were the first to establish evolution as a powerful scientific theory.
A. Pre-Darwinian Evolutionary Ideas
1. Before the 18th century, speculation on origin of species was not scientific.
2. Early Greek philosophers considered some ideas of evolutionary change.
a. Xenophanes, Empedocles and Aristotle developed early ideas about evolution.
b. Fossils were recognized as former life destroyed by natural catastrophe.
c. Lacking a full evolutionary concept, the idea faded before the rise of Christianity.
3. Biblical account of creation became a tenet of faith.
a. Evolutionary views were heretical.
b. Archbishop Ussher calculated 4004 BC as date of life’s creation.
4. French naturalist Georges Louis Buffon suggested that environment modified animal types; set
age of earth at 70,000 years.
B. Lamarckism: The First Scientific Hypothesis of Evolution
1. French biologist Jean Baptiste de Lamarck offered first complete explanation in 1809
(Figure1.4).
a. He convincingly argued that fossils were remains of extinct animals.
b. Lamarck’s mechanism was inheritance of acquired characteristics.
c. He explained long necks of giraffes to stretching efforts of ancestral giraffes.
d. Lamarck’s concept is transformational; individuals transform their own traits to evolve.
e. In contrast, Darwin’s theory is variational or due to differential survival among offspring.
C. Charles Lyell and Uniformitarianism
1. Geologist Sir Charles Lyell established the principle of uniformitarianism (Figure 1.5).
a. Uniformitarianism consists of two important principles:
1) Laws of physics and chemistry remain the same throughout earth’s history.
2) Past geological events occurred by natural processes similar to those observed today.
b. Natural forces acting over long periods could explain formation of fossil-bearing rocks.
c. Earth’s age must be measured in millions of years.
d. Geological changes are natural and without direction; both concepts underpinned Darwin.
D. Darwin’s Great Voyage of Discovery (1831-1836)
1. In 1831, Charles Darwin (almost 23) sailed aboard the small survey ship HMS Beagle.
2. Darwin made extensive observations in the five-year voyage (Figure 1.6, Figure,1.7).
a. Darwin collected the fauna and flora of South America and adjacent regions.
b. He unearthed long extinct fossils and associated fossils of South and North America.
c. He saw fossil seashells embedded in the Andes rocks at 13,000 feet altitude.
d. Observing earthquakes and severe erosion confirmed his views of geological ages.
3. The Galápagos Islands provided unique observations.
a. These volcanic islands are on the equator 600 miles west of Ecuador (Figure 1.8).
b. Galápagos means “tortoise”; the giant reptiles were exploited for food.
c. Each island varied in tortoises, iguanas, mockingbirds and ground finches.
d. The islands had similar climate but varied vegetation.
e. Island species therefore originated from South America and were modified under the varying
conditions of different islands.
f. He wrote that these unique animals and plants were the “origin of all my views.”
4. Darwin conducted the remainder of his work at home in England (Figure 1.9).
a. His collections and notebooks had been sent back before his return in October 2, 1836.
b. His popular travel journal, The Voyage of the Beagle, was published three years later.
c. In 1838, Darwin read an essay on population by Thomas R. Malthus.
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d.
e.
f.
g.
h.
i.
j.
1.4
1.5
Having studied artificial selection, a “struggle for existence” because of overpopulation, gave
him a mechanism for evolution of wild species by natural selection.
He presented his ideas in a private, trial essay in 1844 and began work on a larger volume in
1856.
In 1858, he received a manuscript from a young naturalist, Alfred Russel Wallace,
summarizing the main points of natural selection.
Geologist Lyell and botanist Hooker persuaded Darwin to publish a paper jointly with
Wallace’s paper.
Darwin published a book in 1859: On the Origin of Species by Means of Natural Selection.
1250 copies of first printing sold in one day.
Darwin wrote a series of important additional books in the next 23 years.
Darwin’s Theory of Evolution
A. Darwin’s Theory of Evolution is over 150 years old.
B. Darwinism is now considered as five theories that have somewhat different origins and fates and
cannot be discussed accurately as only a single hypothesis: 1) perpetual change, 2) common descent,
3) multiplication of species, 4) gradualism, and 5) natural selection.
1. Perpetual change is the basic theory of evolution on which the others are based—the world is
constantly changing, as documented by the fossil record that refutes Creationists’ claims.
2. Common descent—all forms of life descended from a common ancestor (Figure 1.10).
3. Multiplication of Species—Species divide and split into different species, which are generally
termed to be reproductively separated populations no longer capable of interbreeding.
4. Gradualism—large differences in anatomical traits that characterize different species originate by
accumulation of many small incremental changes over very long periods of time.
5. Natural selection—explains the selective processes of the environment, through a phenomenon
called adaptation.
C. Darwin’s Explanatory Model of Evolution by Natural Selection (BOX)
1. Observation 1: Organisms have great potential fertility
2. Observation 2—Natural populations normally remain constant in size, except for minor
fluctuations
3. Observation 3—Natural resources are limited
a. Inference 1—A continuing struggle for existence occurs among members of a population.
4. Observation 4—All organisms show organismal variation.
5. Observation 5—Variation is heritable.
a. Inference 2— Varying organisms show Differential survival and reproduction favoring
advantageous traits.
b. Inference 3—Over many generations, natural selection gradually produces new adaptations
and new species.
Evidence for Darwin’s Five Theories of Evolution
A. Perpetual Change
1. The living world is constantly changing in form and diversity.
2. Change in animal life is directly seen in the 540 million-year animal fossil history.
3. A fossil is a remnant of past life (Figure 1.11).
a. Insects in amber and frozen mammoths are actual remains.
b. Teeth and bones can petrify or become infiltrated with silica and other minerals.
c. Molds, casts, impressions and fossil excrement are also fossils.
4. Most organisms leave no fossils; the record is always incomplete and requires interpretation.
B. Interpreting the Fossil Record
1. The fossil record is biased because preservation is selective.
2. Vertebrate skeletons and invertebrates with shells provide more records (Figure 1.11).
3. Soft-bodied animals leave fossils only in exceptional conditions such as the Burgess Shale
(Figure 1.12).
4. Fine fossil sites also include South Australia, Rancho La Brea, the Olduvai Gorge of Tanzania
and dinosaur beds in Alberta, Canada and Jensen, Utah (Figure 1.13).
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5.
6.
7.
8.
9.
C.
D.
E.
F.
Fossils occur in stratified layers; new deposits are on top of older material.
“Index” or “guide” fossils are “indicators” of specific geological periods.
Layers often tilt and crack, and can erode or be covered with new deposits.
Under heat and pressure, rock becomes metamorphic and fossils are destroyed.
The stratification record and inferred evolutionary relationships for two major groups of
African antelopes is given. (Figure 1.14)
Geological Time
1. Sedimentary Rock Layers
a. The “law of stratigraphy” dates oldest layers at the bottom and youngest at the top.
b. Time is divided into eons, eras, periods and epochs. (See inside back cover.)
2. Radiometric Dating
a. In the late 1940s, this dating method was developed that determines age of rocks.
b. Radioactive decay of naturally occurring elements is independent of heat and pressure.
c. Potassium-Argon Dating
1) Potassium-40 (40K) decays to Argon-40 (40Ar) and Calcium-40 (40Ca).
2) Half-life of potassium-40 is 1.3 billion years; half of remainder will be gone at end of
next 1.3 billion years, etc.
3) Calculating the ratio of remaining potassium-40 to amount originally there provides
mathematically close estimate of age of deposit.
d. Rate of decay of uranium into lead can date age of earth itself; error is less than 1% over 2
billion years.
3. Fossil Record of Macroscopic Organisms
a. The Cambrian period of Paleozoic era began about 540 million years ago.
b. Previous Precambrian era occupies 85% of geological time on earth.
c. Little research occurred on Precambrian rocks because they have few oil deposits.
d. Precambrian contains well-preserved fossils of bacteria and algae, casts of lower invertebrates
and many microscopic fossils.
Evolutionary Trends
1. Fossil record allows observation of evolutionary change over broad periods of time.
2. Animals species arise and go extinct repeatedly.
3. Animal species typically survive 1-10 million years; there is much variability.
4. Trends are directional changes in features and diversity of organisms.
5. Horse Evolution Shows Clear Trend (Figure 1.15).
a. From Eocene to Recent periods, genera and species of horses were replaced.
b. Earlier horses had smaller sized and fewer grinding teeth, and more toes.
c. Change occurred in both features of horses and numbers of species.
6. Trends in fossil diversity are due to different rates of species formation and extinction (Figure
1.16).
7. Lineages vary in producing new species or suffering extinction; Darwin provided explanations for
this phenomenon.
Common Descent
1. Darwin proposed that all plants and animals descended from a common ancestor.
2. A history of life forms a branching tree called a phylogeny.
3. This theory allows us to trace backward to determine converging lineages.
4. All forms of life, including extinct branches, connect to this tree somewhere.
6. Phylogenetic research is successful at reconstructing this history of life.
7. Diversity profiles can be reconstructed from fossil record.
Homology and Phylogenetic Reconstruction
1. Darwin saw homology as major evidence for common descent.
2. Richard Owen described homology as “the same organ in different organisms under every variety
of form and function.”
3. Vertebrate limbs show the same basic structures modified for different functions (Figure 1.17).
4. Darwin’s central idea that apes and humans have a common ancestor was explained by anatomical
homologies which was often ridiculed by the media (Figure 1.18).
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5.
Ground-dwelling birds illustrate homologies (Figure 1.19)
a. A new skeletal homology arises on each lineage shown.
b. Different groups located at tips of branches contain homologies that reflect ancestry.
c. Branches of the tree combine species into nested hierarchies of groups within groups.
d. Analysis of the living species alone can reconstruct the branching pattern.
e. The pattern of nested hierarchies forms the basis for classification of all forms of life.
f. Structural, molecular, and chromosomal homologies are all combined to reconstruct
evolutionary trees.
g. Older theories that life arose many times forming unbranched lineages fails to predict the
nested hierarchies of lineages; creationism fails to provide testable predictions; all fail as
scientific hypotheses.
G. Ontogeny, Phylogeny and Recapitulation
1. Ontogeny is the history of development of an organism throughout its lifetime.
2. Evolutionary alteration of developmental timing generates new traits allowing divergence among
lineages.
3. “Ontogeny recapitulates phylogeny” also became known as recapitulation or the biogenetic law.
4. Homoeotic genes guide development of anterior versus posterior body segments.
5. Homebox genes encode a protein sequence that bonds to other genes and alters their expression.
6. German zoologist Ernst Haeckel stated stages of development represented adult forms from
evolutionary history.
7. Haeckel, Darwin’s contemporary, thought that this change was caused by adding new features onto
the end of ancestral ontogeny; but this idea is Lamarckian.
8. Embryologist K.E. von Baer showed early developmental features were simply more widely
shared among different animals groups (Figure 1.20).
9. However, early development can undergo divergence among lineages too.
10. An evolutionary change in timing of development is called heterochrony.
11. Characteristics can be added late in development.
12. Ontogeny can be shortened in evolution; terminal stages may be deleted causing adults of
descendants to resemble youthful ancestors.
13. Organisms are a mosaic of both; ontogeny rarely completely recapitulates phylogeny.
H. Multiplication of Species
1. Evolution as a Branching Process
a. A branch point occurs where an ancestral species splits into two different species.
b. Darwin’s theory is based on genetic variation.
c. Total number of species increases in time; most species eventually become extinct.
d. Much evolutionary research centers on mechanisms causing branching.
2. Definition of species varies and may include several criteria.
a. Members descend from a common ancestral population.
b. Interbreeding occurs within a species but not among different species.
c. Genotype and phenotype within a species is similar; abrupt differences occur between species.
d. Formation of new species is called speciation.
3. Reproductive Barriers
a. Reproductive barriers are central to forming new species.
b. If diverging populations reunite, before they are isolated, interbreeding maintains one species.
c. Evolution of diverging populations requires they be kept physically separate a long time.
d. Geographical isolation with gradual divergence provides the best chance for reproductive
barriers to form (Figure 1.21).
4. Allopatric Speciation (Figure 1.22)
a. Allopatric populations occupy separate geographical areas.
b. They cannot interbreed because they are separated, but could do so if barriers were removed.
c. Separated populations evolve independently and adapt to different environments.
d. Eventually they are distinct enough that they cannot interbreed when reunited.
e. “Sympatric speciation” denotes species formation not involving geographic isolation.
5. Adaptive Radiation (Figure 1.23, 1.24)
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a.
b.
c.
I.
1.6
Adaptive radiation produces diverse species from common ancestral stock.
The Galápagos Islands provided excellent isolation from the mainland and each other.
Darwin’s finches are an example of adaptive radiation from an ancestral finch; finches varied
to assume characteristics of missing warblers, woodpeckers, etc (figure 1.24B).
Gradualism
1. Darwin’s theory of gradualism opposed arguments for a sudden origin or species.
2. He agreed with Lyell; past changes do not depend on catastrophes not seen today.
3. We observe small, continuous changes; major differences therefore require thousands of years.
4. Accumulation of quantitative changes leads to qualitative change.
5. Phenotypic Gradualism
a. This theory states that strikingly different traits are produced in a series of small steps.
b. It remains controversial ever since Darwin proposed it.
c. Mutations that cause substantial phenotypic change are called “sports” (Figure 1.25).
d. Animal breeding has used sports to produce short-legged sheep, etc.
e. Opponents of phenotypic gradualism contend such mutations would be selected against.
6. Phyletic gradualism (Figure 1.26)
a. Predicts that fossils would show a long series of intermediate forms.
b. Fossil record does not show the predicted continuous series of fossils.
c. Some Darwinists contend that fossilization is haphazard and slow compared to speciation.
7. Punctuated Equilibrium
a. Niles Eldredge and Stephen Jay Gould proposed punctuated equilibrium.
b. This theory contends phenotypic evolution is concentrated in brief events of speciation
followed by long intervals of evolutionary stasis.
c. Speciation is episodic with a duration of 10,000 to 100,000 years.
d. Species survive for 5-10 million years; speciation may be less than 1% of species life span.
J. Natural Selection (Figure 1.2)
1. Natural selection gives a natural explanation for origins of adaptation.
2. Rapid evolution by natural selection is found in pepper moths affected by industrial melanism.
3. Birds are able to locate and eat moths that do not match their surroundings.
4. With increasing industrialization, white pepper moths were conspicuous against dark
backgrounds.
5. Birds foraged selectively on white pepper moths, black pepper moths thrived and reproduced.
6. Evolutionists proposed that many structures evolved initially for purposes different from the uses
they have today such as feathers and thermoregulation; exaptation contrasts with adaptation.
Revisions of Darwinian Evolutionary Theory
A. Neo-Darwinism
1. Darwin did not know the mechanism of inheritance.
a. Darwin saw inheritance as a blending of parental traits.
b. He also considered an organism could alter its heredity through use and disuse of parts.
2. August Weismann’s experiments showed an organism could not modify its heredity.
3. Neo-Darwinism is Darwin’s theory as revised by Weismann
4. Mendel’s work provided linkage through inheritance that Darwin’s theory required.
5. The genetic basis of neo-Darwinism is termed the chromosomal theory of inheritance.
B. Emergence of Modern Darwinism: The Synthetic Theory
1. In 1930s, a synthesis occurred that tied together population genetics, paleontology, biogeography,
embryology, systematics and animal behavior.
2. Population genetics studies evolution as change in gene frequencies in populations.
3. Microevolution is change of gene frequency over a short time within a population.
4. Macroevolution is evolution on a grand scale, originating new structures and designs, trends,
mass extinctions, etc.
5. The synthesis combines micro- and macroevolution and expands Darwinian theory.
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1.7
Microevolution: Genetic Variation and Change within Species
A. Definitions
1. Different allelic forms of a gene constitute polymorphism.
2. All alleles of all genes that exist in a population are collectively the gene pool.
3. Allelic frequency is the frequency of a particular allelic form in a population (Figure 1.28)
a. Blood types are coded at codominant alleles IA (type A) and IB (type B) and recessive type i
(O).
b. Since each person carries two alleles; the total numbers of alleles is twice the population size.
c. Dominance describes the phenotypic effect of an allele only, not its relative abundance.
BOX: Hardy-Weinberg Equilibrium: Why Mendelian Heredity Does Not Change Allelic
Frequencies.
B. Protein Polymorphism
1. Protein polymorphism occurs when different allelic forms of a genes encode proteins that often
differ slightly in their amino acid sequences (Figure 1.29).
2. Over the past 45 years, geneticists have discovered far more variation than was previously expected
which is evidence that most species have an enormous potential for further evolutionary change.
C. Genetic Equilibrium
1. In large two-parent populations, genotypic ratios remain in balance unless disturbed.
2. This is called the Hardy-Weinberg equilibrium.
3. It accounts for the persistence of rare traits such as albinism and cystic fibrosis caused by recessive
alleles.
4. Genotype frequency can be calculated by expanding the binomial (p - q)2 where p and q are allele
frequencies.
5. For example, an albino is homozygous recessive and the trait is represented by q 2 in the formula:
p2 + 2pq + q2 = 1.
6. Albinos (homozygous recessive) occur in one in 20,000; therefore q 2 = 1/20,000 and q = 1/141.
7. Non-albino (p) is 1 - q = 140/141.
8. Carriers would be 2pq or 2 x 140/141 x 1/141 = 1/70; one person in 70 is a carrier.
9. Eliminating a “disadvantageous” recessive allele is nearly impossible.
10. Selection can only act when it is expressed; it will continue through heterozygous carriers.
D. Process of Evolution: How Genetic Equilibrium is Upset
1. In natural populations, Hardy-Weinberg equilibrium is disturbed by one or more of five factors.
2. Genetic Drift
a. A small population does not contain much genetic variation (Figure 1.31).
b. Each individual contains at most two alleles at a single locus; a mating pair has a maximum of
four alleles to contribute for a trait.
c. By chance alone, one or two of the alleles may not be passed on.
d. Chance fluctuation from generation to generation, including loss of alleles, is genetic drift.
e. There is no force causing perfect constancy in allelic frequencies.
f. The smaller the population, the greater the effect of drift.
g. If a population is small for a long time, alleles are lost and response to change is restricted.
h. A bottleneck is a large reduction in the size of a population. It is a form of genetic drift that
increases the rate of evolutionary change.
3. Nonrandom Mating
a. If two alleles are equally frequent, one half of the population will be heterozygous and one
quarter will be homozygous for each allele.
b. In positive assortative mating, individuals mate with others of the same genotype.
1) This increases homozygous and decreases heterozygous genotypes.
2) It does not change allelic frequencies.
c. Inbreeding is preferential mating among close relatives.
1) Inbreeding increases homozygosity.
2) While positive assortative mating affects one or a few traits, inbreeding affects all
variable traits.
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4.
5.
6.
1.8
1.8
3) Inbreeding increases the chance that recessive alleles will become homozygous and
expressed.
Migration
a. Migration prevents different populations from diverging.
b. Continued migration between Russia and France keeps the ABO allele frequencies from
becoming completely distinct.
Natural Selection
a. Natural selection changes both allelic frequencies and genotypic frequencies.
b. An organism that possesses a superior combination of traits has a higher relative fitness.
c. Some traits are advantageous for certain aspects of survival or reproduction and
disadvantageous for others.
d. Sexual selection is selection for traits that obtain a mate but may be harmful for survival
(Figure 1.32).
e. Changes in environment alter selective value of traits making fitness a complex problem.
f. Quantitative traits show continuous variation with no Mendelian segregation pattern.
1. Such traits are influenced by variation at many genes.
2. Such traits show a bell-shaped frequency distribution.
g. Stabilizing selection favors the average and trims the extreme. (Figure 1.33B)
h. Directional selection favors an extreme value to one side. (Figure 1.33C)
i. Disruptive selection favors the extremes to both sides and disfavors the average. (Figure
1.33D)
Interactions of Selection, Drift and Migration
a. Subdivision of a species into small populations that exchange migrants promotes rapid
evolution.
b. Genetic drift and selection allow many combinations of many genes to be tested.
c. Migration allows favorable new combinations to spread.
d. Interactions of all factors produce change different from what would result from one alone.
e. Perpetual stability almost never occurs across any significant amount of evolutionary time.
Macroevolution: Major Evolutionary Events and Processes
A. Speciation and Extinction through Geological Time
1. A species has two possible fates: become extinct or give rise to new species.
2. Rates of speciation and extinction vary among species.
3. Lineages with high speciation and low extinction produce the greatest diversity.
4. Lineages whose characteristics increase probability of speciation and confer resistance to
extinction should come to dominate.
5. Species selection is differential survival and multiplication of species based on variation among
lineages.
6. Species-level properties include mating rituals, social structuring, migration patterns, geographic
distribution, etc.
7. Some mammalian lineages have a “harem” system, others do not.
B. Mass Extinctions
1. Periodic events where huge numbers of taxa go extinct simultaneously are mass extinctions
(Figure 1.34).
2. The Permian extinction occurred 250 million years ago; half of the families of shallow water
invertebrates and 90% of marine invertebrates disappeared.
3. The Cretaceous extinction occurred 65 million years ago and marked the end of the dinosaurs
and many other taxa.
4. Mass extinctions appear to occur at intervals of 26 million years.
a. Some consider them artifacts of statistical or taxonomic analysis.
b. Walter Alvarez proposed that asteroids periodically bombard the earth (Figure 1.35).
c. Catastrophic species selection would result from selection by these events; for instance,
mammals were able to use resources due to dinosaur extinction.
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Lecture Enrichment
1. Almost continuously throughout this course, students can be asked to design an experiment to test a particular
hypothesis being discussed.
2. Ask students for examples of the scientific method in their everyday lives, such as fixing dinner, determining
how to dress for the day's weather and activities, or handling problems with a car that doesn't work.
3. Students can search local newspapers for examples using the scientific method (e.g., testing consumer products,
recalls, reports on medical research, jury decisions based on forensic evidence, etc.). Bring in a tabloid
newspaper making fabulous claims and ask why it does not meet science standards.
4. Discuss the difference between scientific observations of the natural world and superstitions such as those
associated with Friday the thirteenth and black cats. Examples involving Bigfoot, the Loch Ness monster,
spontaneous human combustion, living dinosaurs in remote areas, and other modern misbeliefs related to
animals are given in the Skeptic and Skeptical Inquirer magazines.
5. Discuss why it is possible to prove a hypothesis or theory false but not prove it true. Be careful not to fall into
the postmodernist or constructivist view of science knowledge being merely a mental construct, no better or
worse than tribal beliefs, etc., or being tentative to the point of merely awaiting falsification.
6. Most students believe the world is spherical. Only students who have flown in the Concorde jetliner have direct
observational evidence for this. Yet they believe the photos by astronauts, and phoning a person in China
awakes them in a time zone 12 hours different from us. Such indirect evidence fortifies the model of a spherical
earth. This illustrates science relies on reasoning to make sense of observational data.
7. Clarify the fact that Lamarck was the first to try to develop a possible mechanism for evolution. He should be
considered among the great biologists of history, rather than just the “one who got evolution wrong.”
8. Speculate how Darwin would have reacted to Mendel's work if he had read it; Darwin had a copy of the
publication of Mendel's paper, but the pages had never been cut so that it could be read.
9. Note that both Darwin and Wallace had extensive travel experiences where they saw a wide range of organisms
before they formulated their theory of evolution by natural selection. Biology is so complex and laden with
emergent properties that it is not possible to discover one underlying law, as in physics and chemistry, and then
extrapolate to all cases. The need for a wide range of observational experiences in biology is therefore a
difference in philosophy of science between the life and physical sciences that many students will not perceive.
10. In a modern age of public relations, few students will comprehend why Darwin waited over twenty years from
his seminal trip on the HMS Beagle to publish his theory. One of the topics to consider is Darwin's feelings for
his wife, who was a very religious woman, and the impact that the theory of natural selection and evolution had
on those who considered the theory of special creation to be absolute truth, which students should understand.
11. Students do not immediately internalize the meaning of terms such as “allopatric” and “sympatric.” Since you
will not be using these terms across the course, the concept is most efficiently taught using examples and
referring to the cases rather than generalizing.
12. Students who have already completed a course in botany will have an understanding of the ability of plants to
speciate sympatrically via polyploidy. Other students will be puzzled why animals and plants vary so greatly on
this issue.
Commentary
Background: Professors that are new to a college or university may consult with veteran professors about the state’s
high school biology and other science requirements. In addition, the proportion of students that come from farm or
urban backgrounds will provide a major indicator of student experiences. Most high school science texts discuss the
“scientific method” as a very cookbook or lock-step method. And most college undergraduates do not have genuine
experience with open-ended and purposeful science research, nor the breadth of experience to place limited research
experience in a full perspective.
Misconceptions: Many students see science as a body of encyclopedic knowledge and authority, and do not
recognize an underlying scientific attitude or process. Some students have been told that science is only process,
and have no appreciation for the role of the general public recognizing germ theory, for instance. Most citizens view
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science as done only by scientists and do not consider the trouble-shooting done by a medical doctor or auto
mechanic to be in any way “scientific.” Most consider scientists always “open minded” and do not recognize that
experiments often close the door to hypotheses that don’t work out. In many states, physics classes are not
commonly taken in high school; this may be their first exposure to physics and many students will misunderstand
the laws of physics as preventing evolution. A large portion of college students believe that dinosaurs and humans
were on earth at the same time, and a similar proportion question the validity of the theory of evolution but without
much depth of knowledge about it. A large proportion view evolution as “survival of the fittest” without
recognizing that survival is only useful if it promotes more reproduction.
Schedule: Students may lack the book assignment the first day of class but this is the point where an instructor
establishes ground rules of quizzes, testing, whether notes will be given in outline form, etc. If you use in-class
questioning, you might consider beginning with something like “Why is life on earth so diverse?”
Background: The concepts of multiple alleles and recombination are not explained in many secondary biology
texts. Algebra skills are necessary for students to understand the Hardy-Weinberg formula and high school math
requirements vary by state. Some African-American students will be very aware of the sickle-cell gene. The comet
and meteorite impact theories have gone from speculative to fairly well accepted in the last few decades and the
instructor will probably face students who were taught previous uncertainties. Breaking news on recent major fossil
finds in China and Africa make evolution a timely topic to cover. And new discoveries requiring reinterpretation of
our phylogeny will cause this chapter to present new or different concepts from what students may have learned in
high school biology. Visuals of fossils will help students see the distinctions described in this chapter. Some
students will have some concerns with this chapter based on religious background but an honest and clear
explanation of the current status of our scientific knowledge should help.
Misconceptions: Most students view mutations as rare and the only source of genetic variation. Dinosaurs are a
hot topic now covered heavily in K-12 science curricula; however, new developments make many textbooks
obsolete; therefore the college instructor will have to deal with many misconceptions. Some students and even
molecular biologists will not understand why classifications change. Why can’t systematists just settle on one set of
higher taxa and stick with it? While ongoing changes may seem casual and arbitrary, there is a complex rationale
for the evolutionary schema that students can understand.
Schedule: An instructor may vary considerably in how much background history, philosophical setting, etc., to
provide before introducing Darwin’s voyage, etc. Speed of coverage of population genetics concepts will also vary
greatly depending on students’ previous coursework.
ADVANCED CLASS QUESTIONS:
1. Scientists use the scientific method to gather information about the natural world. Can this include the past?
Does how a forensics expert reconstructs a crime scene differ in substance from how an evolutionary biologist
reconstructs ancient ecology from fossil evidence?
2. When utilizing the scientific method, hypotheses can be proven false, but not true. Does this mean all science is
conjecture until disproved? Can anyone explain the “uncertainty principle” and the ability of scientists to
calculate the tolerance limits of their knowledge?
3. What evidence exists that all living things evolved from a common ancestor? How does this concept explain
the unity of life forms?
4. Animal ecology experiments can be classified in two general categories. Ecologists can bring an animal into
the laboratory, isolate it in a chamber where they can determine all the environmental conditions affecting it and
then alter one variable. Or they can study the animal in the wild and attempt to determine why it occurs in
certain natural habitats. Using terms given in the text for science methodology, explain the benefits of both
systems.
5. Will evolution occur if there is no variation in a population, if the only variation is acquired and not inherited or
if all progeny survive and equally reproduce?
6. Could bacteria and humans possibly share a common ancestor; and what evidence do we have?
7. Why are an insect wing and a bird wing not considered evidence of relatedness?
8. The presence of vestigial structures suggests that the process of adaptation is not necessarily purposeful. Why?
9. How can the scientific method be used to test the concept of evolutionary descent if no one was present in the
past to witness it?
10. Why is adaptive radiation more prevalent when there is less competition, as in the case of the finches on the
Galápagos or the mammals following the dinosaur extinction?
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