|Themes > Science > Life Sciences > Human Races > Origns of Human Populations|
Races and other groups
A race can be defined as a large population that has a gene pool that is substantially different from that of other large populations.
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.
Races arise by the same mechanisms as species: geographic and reproductive isolation, adaptation (natural selection) and genetic drift.
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.
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.