1. The allele is maintained at high levels because the incidence of malaria is high in these regions, against which the sickle cell allele confers resistance. An individual homozygous for sickle cell anemia will die of sickle cell anemia; an individual homozygous for no sickle cell anemia at all runs the risk of dying of malaria. The heterozygote, while perhaps exhibiting some traits of sickle cell anemia, isn't likely to die of sickle cell anemia or malaria.
2. The frequency is lower among African Americans because malaria does not exist as a selective pressure in North America.
3. Soot-darkened trees and pollution killed light-colored lichens, so light-colored moths stood out on the dark background and were eaten. Therefore, fewer light-colored moths survived to reproduce and a greater number of dark-colored moths reproduced and passed on their dark-color genes. Industrial melanism refers to the increase of melanin production by organisms to blend into the sootier atmosphere generated by industry.
4. The fossil record, molecular record, homology, development, vestigial structures, parallel adaptation, and patterns of distribution support macroevolution.
5. In Darwin's day they age-dated rocks by the position of various strata and could only give ages in relation to one another. Now radioactive dating is based on the half-life decay of certain radioisotopes, a definite quantity.
6. More closely related species have a greater number of DNA sequences in common and more distant relations have a greater number of differences, based on a progressive accumulation of DNA change.
7. Homology is the development of seemingly different structures from the same ancestral source (wings in birds and fins on fish). It shows that change has taken place slowly and very demonstrably from earlier forms.
8. Whales are mammals, which have pelvic bones. Despite no apparent function, homology would dictate the presence of the structures somewhere in some form. "Useless" structures such as these are referred to as vestigial structures.
9. Convergent evolution is seen in organisms which are vastly different yet seem to have evolved the same mechanisms to deal with specific environmental pressures (such as albinism and blindness in cave organisms).
10. Darwin showed that an isolated population of organisms rapidly adapts and evolves to fit their habitat-with their closest relatives being those encountered in the closest continental region.
11. The gradualists believe that all change was gradual, with many transitional forms. The punctuated view is that little change occurred over long periods of time with occasional sudden large evolutionary changes.
12. Scientific creationism is not truly scientific because it is based on beliefs rather than observations and it does not infer its principles from observations.