Monday, February 20, 2006


Not only did we, so far, escape nuclear destruction during the Cold War, but look at the following:

"We [are] dealing with the unusually high level of genetic uniformity in the human species, despite superficial appearances. If you take blood and compare protein molecules, or if you sequence genes themselves, you will find that there is less difference between any two humans living anywhere in the world than there is between two African chimpanzees. We can explain this human uniformity by guessing that our ancestors, but not the chimpanzees, passed through a genetic bottleneck not very long ago. The population was reduced to a small number, came close to going extinct, but just pulled through. There is evidence of a fierce bottleneck—perhaps down to a population of 15,000, some 70,000 years ago, caused by a six-year 'volcanic winter' followed by a thousand-year ice age. Like the children of Noah in the myth, we are all descended from this small population, and that is why we are so genetically uniform. Similar evidence, of even greater genetic uniformity, suggests that cheetahs passed through an even narrower bottleneck more recently, around the end of the last Ice Age.

"Some people may find the evidence of biochemical genetics unsatisfying because it seems not to square with their everyday experience. Unlike cheetahs, we don't 'look' uniform. Norwegians, Japanese and Zulus all do look rather dramatically different from one another. With the best will in the world, it is intuitively hard to believe what is in fact the truth that they are 'really' more alike than three chimpanzees who look, to our eyes, much more similar." —Dawkins, THE ANCESTOR'S TALE, p. 405.

But Dawkins' claim does not square with the idea that to a white male, three Chinese tailors might look all so very much alike because we just don't look very closely. People who work closely with chimps probably have no trouble distinguishing them and seeing distinct personalities at work and play whereas a casual zoo visitor might think all the chimps in the cage look alike.


Again we come across the idea that culture does contribute to evolution. I mean if a bird's song can attract a mate of his own kind, then why not a hymn or a chant? Fortunately, we are not so bound up as the bird.

"Our (relatively) recent worldwide diaspora out of Africa has taken us to an extraordinarily wide variety of habitats, climates and ways of life. It is plausible that the different conditions have exerted strong selection pressures, particularly on externally visible parts, such as the skin, which bear the brunt of the sun and the cold. It is hard to think of any other species that thrives so well from the tropics to the Arctic, from sea level to the high Andes, from parched deserts to dripping jungles, and through everything in between. Such different conditions would be bound to exert different natural selection pressures, and it would be positivelY surprising if local populations did not diverge as a result. Hunters in the deep forests of Africa, South America and South-East Asia have all independently become small, almost certainly because height is a handicap in dense vegetation. Peoples of high latitude, who, it has been surmised, need all the sun they can get to make vitamin D, tend to have lighter skins than those who face the opposite problem—the carcinogenic rays of the tropical sun. It is plausible that such regional selection would especially affect superficial characteristics like skin colour, while leaving most of the genome intact and uniform.

"In theory, that could be the full explanation for our superficial and visible variety, covering deep similarity. But it doesn't seem enough to me. At the very least, I think it might be helped along by an additional suggestion, which I offer tentatively. It takes off from our earlier discussion about cultural barriers to interbreeding. We are indeed a very uniform species if you count the totality of genes, or if you take a truly random sample of genes; but perhaps there are special reasons for a disproportionate amount of variation in those very genes that make it easy for us to notice variation, and to distinguish our own kind from others. This would include the genes responsible for externally visible 'labels' like skin colour. Yet again, I want to suggest that this heightened discriminability has evolved by sexual selection, specifically in humans because we are such a culture-bound species. Because our mating decisions are so heavily influenced by cultural tradition, and because our cultures, and sometimes our religions, encourage us to discriminate against outsiders, especially in choosing mates, those superficial differences that helped our ancestors to prefer insiders over outsiders have been enhanced out of all proportion to the real genetic differences between us. No less a thinker than Jared Diamond has supported a similar idea in The Rise and Fall of the Third Chimpanzee. And Darwin himself more generally invoked sexual selection in explanation of racial differences." Dawkins, THE ANCESTOR'S TALE, pp. 410-411

No comments: