Researchers have been surprised (imagine that!) by their analyses of genomes from dozens of distinct human populations from around the globe that there is virtually no dramatic genome variation among the human species.
-- From "Among Many Peoples, Little Genomic Variety" by David Brown, Washington Post Staff Writer 6/22/09
Population geneticists expected to find dramatic differences as they got a look at the full genomes -- about 25,000 genes -- of people of widely varying ethnic and geographic backgrounds. Specifically, they expected to find that many ethnic groups would have derived alleles that their members shared but that were uncommon or nonexistent in other groups. Each regional, ethnic group or latitude was thought to have a genomic "signature" -- the record of its recent evolution through natural selection.
Instead, it is "random genetic drift" that appears to be more important in sculpting our genes. Drift describes the chance loss of genetic variation that occurred not only in the out-of-Africa migration, but through all of human history as famine, climate change or war caused populations to crash and then recover.
Despite those calamities, it appears that all contemporary populations ended up largely the same, or only crudely distinguishable from one another, on the genome level.
Of course, small variations can result in dramatic differences. Skin color is perhaps the most obvious.
Such clear ethnic distinctions are the exception, however, defying the expectations of many researchers. That may have been a product of the way scientists have studied genes over the last century. [. . . clouded by Darwin, perhaps]
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