Race and Skin Color

Compared to the other Great Apes, or Hominoids, if you prefer, we human are a remarkably homogeneous at the genetic level.  Surprisingly enough, populations of only a few thousand gorillas have more genetic variation across their species than the seven gazillion humans encompass.  This is likely due to our species passing through a few major bottlenecks in the last 100,000 or so years.

This fact is a major reason that modern science is convinced that the concept of race is pretty meaningless so far as humans are concerned.  Still, we don't all look alike.  Our brains are exquisitely tuned to noticing small differences among us, and most of us can recognize thousands of different faces.  Not only that, but there are a few differences among humans that correlate with large scale origins (or oranges, as the maximum leader, himself a member of the orange tribe, might say), with the most obvious being skin pigmentation.

Race, as they say, is a social construct, but skin color is a physical trait and it has been used to justify some of the most egregious types of discrimination and persecution.   Interestingly enough, the genes that determine human skin coloration (and there are a half dozen or so) all seem to predate our species - they existed before H. sapiens, and were present in the humans that left Africa.  These genes control the expression of the two kinds of melanocytes, brown ones and reddish ones.

One such gene drastically downregulates these melanocytes, and is present virtually all modern Europeans and many Asians.  Interestingly enough, it does not seem to have been present in many ancient Europeans, many of whom apparently had blue eyes and dark skin.

Dark skin is an evolutionary disadvantage if you live in Northern Europe, because it makes it hard to synthesize enough vitamin D, and conversely, light skin in the most sunlit parts of the tropics gives you skin cancer.  Thus it appears that skin color differences are a direct result of natural selection acting on the same set of genes all races brought out of Africa.

There are some exceptions, notably the Tasmanians, but it's plausible that genetic drift, combined with thousands of years of isolation, meant that the genes necessary for light skin in their dark environment had been lost before they got there.

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