Terms to know: natural selection, fitness, adaptation, genetic (heritable) variation, population, species, mutation.

Questions:

1. What are the four conditions (Darwin's four postulates) that are necessary and sufficient for evolution through natural selection to occur?  Have these conditions been studied in nature?  If so, do these conditions typically occur in populations? What results in these conditions being present?  Clearly explain why each condition is necessary if natural selection is to occur.
2. Each of the following describes a real situation.  Apply the theory of natural selection to explain how each situation has evolved.  Consider the four things that must initially (before the situation described evolved) have been true in each population for natural selection to have had this effect. Explain why each of these is necessary if natural selection is to occur.  Correctly apply the terms "fitness" and "adaptation" to each situation.  Since these are real examples, you may be expected to know them, and the terminology that applies to them, on exams.
1.   In North America, within many endothermic ("warm-blooded") species, body size is larger in northern populations than it is in southern populations.  This phenomenon is called "Bergman's Rule." For geometric reasons, animals with larger bodies have higher volume relative to surface area.  Heat is stored in an animal's volume, but gained or lost across the surface area.  Given these facts, explain why natural selection is expected to cause the observed latitudinal trend in body size.
2.  Many species that are poisonous (eating these organisms causes sickness or death) or venomous (these organisms produce a poison which they can inject into another organism) are also brightly colored.  It is thought that predators learn or evolve to avoid these brightly colored, poisonous or venomous species.  Such bright coloration in a poisonous or venomous species is called warning or "aposematic" coloration. Explain how bright coloration would have evolved in poisonous or venomous species through natural selection.
3.  Some species of prey animals, eaten by predators, have bright coloration that is very similar to the bright coloration of a poisonous or venomous species.  For example, viceroy butterflies (which are non-toxic) strongly resemble monarch butterflies (which cause birds that eat them to become extremely sick.)  This phenomenon of a non-poisonous species resembling a poisonous species is called Batesian mimicry.  Explain how bright coloration that mimics the bright coloration of a poisonous or venomous species would have evolved in a non-poisonous, non-venomous species through natural selection.
4.  Plant leaves are susceptible to environmental moisture; if there is too much moisture, they can mold, while if there is not enough, water is lost through the leaves through the process of transpiration and the plant can wilt.  Leaf size and shape affect the rate at which water is lost.  Small leaves have a larger layer of dead air space around them and lose water at a lower rate, per leaf area, than do large leaves.   In tropical rainforests, plants tend to have large flat leaves.  In deserts, they have small leaves.  Explain how leaf size in each environment would have evolved through natural selection.
5.  Fish and salamanders that live in caves where it is completely dark do not have eyes, although it is thought that they evolved from ancestors that had eyes.  Explain how a lack of eyes would have evolved through natural selection (HINT: it is energetically costly to produce and maintain body structures such as eyes.)
6. The shells of turtles are thought to be an adaptation that protects turtles from predation. Explain how the presence of shells would have evolved (from a shell-less ancestor) through natural selection.
7. The long necks of giraffes allow them to eat leaves from tall trees that cannot be reached by other mammals.  Clearly explain how long necks would have evolved through natural selection, assuming that the ancestral species to giraffes had short necks.
3. Based on the lecture material and the material in Chapters 1 and 3 of your textbook, explain how natural selection has occurred in each of the situations described below.  State the four postulates of natural selection and explain how each has been evaluated for each situation.  Then state whether the result in the population is as predicted by natural selection.
1.  Bill size in Darwinís finches
2.  AZT resistance in HIV
4. What causes mutations to occur?  Do the causes of a mutation relate to whether or not the mutation is adaptive?
5. What is the ultimate source of genetic variation in populations?
6. One population of spruce trees occurs in a bog, an environment with acidic soil.  Another population of spruce trees occurs in an environment with basic soil.  In which population do you think a mutation for acid tolerance would be most likely to occur?  Why?
7. Evolution through mutation alone is usually a very slow process; its effects are hardly detectable.  Given this fact, what is the main reason evolutionary biologists are interested in mutation?
8. At what rate do mutations typically occur?  Is it the same for all genes and all organisms?
9. How could the rate of mutation be an adaptation, evolved through natural selection, even if the specific mutations that occur may or may not be adaptive?
10. In general, are most mutations that occur adaptive? Why/why not?