Download Self-study Problems #1: Evolution

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Self-study Problems #1: Evolution - Answers
1. Give a brief definition of evolution (in the sense of an observable fact).
Change in the frequency or magnitude of heritable characteristics of a population of organisms
over generations.
2. Give an example of evolution that has actually been observed.
Change in frequency of dark and mottled moths in Manchester before to after the Industrial
Revolution. OR Change in beak depth of Galapagos Island finches during a drought. OR Change
in frequency of drug resistance among bacteria that infect humans. OR… etc.
3. Define catastrophism.
The view that geological strata and fossils are explicable by a series of huge events unlike any in
known history, like world-covering floods that killed and buried all living things, which then
started anew.
4. Define uniformitarianism.
The view that geological strata and fossils are explicable by the action of the same processes we
observe today, like deposition of sand by a river, accumulating their effects over a very long
period of time.
5. Is Darwin’s theory of evolution catastrophist, or uniformitarian? Why?
Uniformitarian, because it involves only processes that we observe today (reproduction of
offspring that imperfectly resemble their parents, many not surviving or reproducing, etc.), but
acting over a long time.
6. List the three conditions (“postulates”) that underlie Darwin’s theory of evolution.
1. More organisms are born than survive and reproduce.
2. Individuals vary in ways that affect how well they survive and reproduce.
3. Some of that variability is heritable. OR Offspring tend to resemble their parents.
7. If Darwin’s three conditions or postulates are true, what happens?
Natural selection, which may or may not cause evolution
8. Imagine a study of a population of a certain species of flea living in a container in a lab. The
researchers make every measurement and observation imaginable of every individual flea
over 500 generations, and absolutely nothing about the population of fleas changes over time.
a. Did evolution occur?
No. OR None that could be detected
b. Did natural selection occur? Explain.
Yes. The most successful type was already the most common type, so no change occurred.
This is called stabilizing selection.
Intro to Biological Anthro F 2008 / Owen: Self-study problems #1
p. 2
9. If living things reproduced only by making exact clones of themselves, would they evolve?
Explain.
No. There would be no variation in fitness, as required by the second postulate. Since all
individuals would be the same, no selection could occur, and no change could accumulate.
10. If we find a watch, we can justifiably infer a watchmaker. What is so different about living
things that we don’t necessarily have to infer a designer? Explain briefly.
Living things reproduce themselves imperfectly, making all three postulates possible, and thus
making the process of evolution possible. Watches do not reproduce, so there can be no
variation in how well they survive and reproduce, so there can be no natural selection, so they
cannot evolve; they must be made by a watchmaker.
11. Imagine that while studying mythical Malawi marsh mice, Dr. Smith observes that adult
mice with longer-than-average tails have twice as many babies as do mice with average or
shorter tails. On the other hand, their principle predator usually catches the mice by their
tails, so mice with shorter-than-average tails are 10% more likely to survive to adulthood. Dr.
Smith is planning to collect detailed census data of these mice for the next twenty years.
a. Assuming that no other factors come into play, should Dr. Smith expect the average
length of the mice’s tails to stay the same, get longer, or get shorter?
The tails should get longer.
b. Why?
The longer-tailed mice leave many more offspring, but have only a slightly
lower rate of survival. Even though slightly fewer longer-tailed mice survive to
adulthood, those that do survive leave many more offspring each than do the average
and shorter-tailed mice. These additional offspring of the survivors more than make up
for the fact that each long-tailed mouse was a bit less likely to survive long enough to
breed.
c. Assuming that no other factors come into play, by the end of the project, should Dr.
Smith expect the mice to be better adapted to avoid predation, or less well adapted?
They will be worse adapted to avoid predation – but better adapted to leave offspring.
12. Complete this sentence: Natural selection acts on ____individuals_____________________,
potentially causing changes in _____the frequency or magnitude of traits in the population__
__________________________________________________________________________.