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1. Discuss organic variation and environmental changes as causes of change in living population.

2. Explain the theory that reduction of the canine teeth is related to tool-making.

3. The theory of recapitulation is often stated: "ontogeny recapitulates phylogeny."  Does this statement accurately describe the facts?  Explain.

4. Frogs (Eleutherodactylus) were not found in Bermuda before being introduced by humans in 1880 but were prevalent in the islands of the West Indies.  Can you explain why they were found in one location and not the other?

5. The evolutionary history of mollusks and reptiles is known much better than that of flatworms.  Why?

6. The Kaibab squirrel has long ears and a white belly and lives on the north rim of the Grand Canyon.  The Abert squirrel, which lives on the south rim, is quite similar in appearance although it has a black belly.

     (a) How can you account for the presence of these two similar, but distinguishable, populations?

     (b) What possible futures might await these squirrels if the canyon should be obliterated?

7. Fossil evidence indicates that evolutionary changes in honeybees have taken place unusually slowly.  Can you think of a possible reason why natural selection might operate particularly slowly in this group?

8. Most of the so-called "living fossils" are found in the sea.  Can you think of a reason for this?

9. Considering the strong selection pressure against the gene for hemophilia, what reasons can you give for the continuing presence of the gene in the human population?

10. How can the Darwinian theory of evolution account for the long neck of the giraffe?  How does this differ from Lamarck's explanation?

11. Under what circumstances is hybridization between species selected against?

12. There are polyploid animals in some groups, but they are far less frequent than they are among plants, particularly perennial plants. Why do you think this might be so?

13. Could artificial selection by human beings (as for dogs) eventually lead to the production of new species? Outline the basis for your answer.

14. Can species ever originate in a single step? If so, what are some of the ways in which this could occur?

15. How can you tell if a new species will give rise to a whole new group of organisms? Under what circumstances is it most likely to do so?

16. Why do you think that at least 2 billion years of evolution preceded the origin of multicellularity, and more than 3 billion years preceded the invasion of the land? What kinds of information would you need to test your ideas?

17. There seems to be on iridium layer preserved in the rocks from four of the five major periods when mass extinction occurred. How could one account for these four events?

18. In Central Africa there is a low frequency of a third hemoglobin allele called C, in addition to the A and S alleles found in sickle cell anemia among the Bantu people. Individuals that  are heterozygous for C and the normal allele A are susceptible to malaria just as AA homozygotes are, but CC individuals are resistant to malaria – and do not develop anemia! Assuming that the Bantu people entered Central Africa relatively recently from a land where malaria is not common (we think this is what happened), and that among the original settlers both C and S alleles were rare, can you suggest a reason that CC individuals have not become predominant?

19. In Fred Hoyle’s science fiction novel, The Black Cloud, the earth is approached by a large interstellar cloud of gas. The cloud orients itself around the sun. Scientists soon discover that the cloud is feeding, absorbing the sun’s energy though the excitation of electrons in the outer energy levels of cloud molecules, a process similar to photosynthesis that occurs on earth. Different portions of the cloud are isolated from one another by associations of ions created by this excitation. Electrons currents pass between these sectors, much as they do on the surface of the human brain, endowing the cloud with self-awareness, memory, and the ability to think. Using static electricity produced by static discharges, the cloud is able to communicate with humans and describe its history, as well as to maintain a protective barrier around itself. It tells human scientists that it once was smaller, having originated as a small extrusion from an ancestral cloud, but has grown by the adsorption of molecules and energy from stars like our sun, on which it has been grazing. Soon the cloud moves off in search of other stars? Is it alive? Defend your position.

20. While the first organisms may have subsisted on organic molecules in the primordial soup, it seems clear that photosynthesis evolved very early in the history of life. Since light provides an inexhaustible source of energy, why do you suppose that heterotrophs and food chains ever evolved? Why aren’t all organisms autotrophs?