A. Gene pools can be compared in terms of the frequencies of alleles at polymorphic loci, although for complex traits, such as skin color and body form, we cannot analyze specific loci and alleles readily as yet.

B. Large populations are specified in the definition of race as a matter of practicality. There are many very small populations that are quite deviant because of genetic drift and founder effect.

C. The number of races is arbitrary. The "splitters" can name several dozen. The "lumpers" may see only three (African, Caucasian, Asian). The urge to classify is a human trait; the results at best are an approximation to biological reality.

D. In any list of races, some races will be closer genetically to each other than they are to other races. E.g. Amerinds came from Asia and have many of the same alleles found in present-day Asians but rare or absent in Europeans and Africans.

E. Each of these races consists of local races or local populations.

F. Races are separated from each other more by our system of classification than by major genetic differences. A few, such as Polynesians and Australians, have been separated from other groups for tens of thousands of years. However, most have had some gene exchange, and often there are smaller populations that are intermediate genetically between major races.

A. A special form of genetic drift is founder effect, in which a population is founded by a small group that may be unrepresentative of the parent population.

B. During the tens of thousands of years that Homo sapiens has existed, the population lived in small tribes, where genetic drift and founder effect were strong forces.

C. As our ancestors spread over the continents, natural selection undoubtedly favored different gene pools in different environments.

 

1. Dark skin was favored in tropical areas because it protects against ultraviolet light. Light skin is favored elsewhere because some ultraviolet is necessary for synthesis of vitamin D.

2. A high ratio of body surface to volume is favored in hot areas so that body heat can be dispersed. A low ratio is favored in cold areas so that heat is conserved.

3. Most Africans and their descendants have an allele at the Duffy blood group locus that makes them resistant to vivax malaria.


D. Cultural practices also can alter fitness of different genotypes: e.g. lactase persistence.

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