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Mechanisms of Human Differentiation
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Mechanisms of Differentiation
The mechanisms of human differentiation are driven by five principal elements: migration, isolation, environment, genetic variation, and time. Migration contributes to differentiation when it exposes a population to novel environments. Racial differentiation results from sustained reproductive isolation of populations exposed to differing environments. Genetic variation occurs randomly in individuals and is significant if it results in an inheritable advantage that is propagated over time throughout a population. Racial differentiation is determined by inheritable characteristics, genetic polymorphisms, regulated by genes in different areas of the human genome.
The passage of time is necessary for significant differentiation to take hold. If a chance mutation in an isolated population results in an individual having purple hair and her distinctive curls attract suitors, in time her novel hair color could appear significantly in her population. If the mutation was accompanied by enhanced color vision and an increase in the size of the telencephalon, the beneficial changes could be the start of a new smart, sharp-eyed, purple haired race.
Ancestors in Isolated Populations
A person's genetic makeup is determined by his ancestors: 2 parents, 4 grandparents, 8 great-grandparents, etc. The potential number of ancestors for one individual is 2 to the nth power, where n is the number of past generations. This works for the first few generations, but the total number of ancestors by the 33rd generation, at about 1,200 A.D., reaches 8.5 billion. This is absurd, since it exceeds the total world population at the time, about 400 million, and would make everyone alive today related to everyone else. The 2 to the nth power formula is ultimately incorrect because it ignores multiple roles in the lineage, as when cousins marry cousins, making a line of potential ancestors vanish. Two ancestors in the same generation could have had the same grandparents, so their ancestral lines converge. Also, following death of a spouse, or divorce, an ancestor can remarry and create an additional line of ancestry. Restrictions on the number of available suitable mates can lead to situations such as a great-great-grandfather also being an individual's great-great uncle.
Effects of Population Size
The number of potential ancestors is limited by the size of isolated populations. When the Pilgrims landed in Plymouth in 1620, they numbered 102. Only 53 survived the first winter. A generation later, in 1645, the population of Plymouth Colony had grown to about 1,600, mostly through subsequent migrations, but partly involving the original settlers. Although Pilgrims disapproved of first-cousin marriages, descendants of the original settlers included cousins and half-siblings.
In 1,200 A.D., the time of the Fourth Crusade, the population of the American continent (American Indians) was isolated from populations in Europe and all other regions. At that time, Pacific Islanders, and Australian and Papuan Aborigines, were also isolated, and interactions between other racial groups were limited and remained so until the late 15th century. A common ancestor between a white European and an American Indian would have lived 350 centuries earlier.
Culture and Ethnicity
Human differentiation requires the concurrence of several of the five principal elements. If all other elements are present, but only for a brief time, differentiation does not occur. Even over extended periods of time, cultural and ethnic divisions between groups that are not isolated do not result in racial differentiation. In the first century B.C., Julius Caesar noted the division of the inhabitants of Gaul between Belgians, Aquitani, Celts, and neighboring Germans, all of which remain racial whites despite twenty centuries of ethnic and national divisions in western Europe. Ethnicity is not race.
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