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Sep. 4th, 2007 (UTC)

Very nice rant! A couple of comments:

People who claim we've stopped evolving because we've cured most major causes of death are more than wrong; they're ironically wrong. If genes predisposing to nearsightedness, say, proliferate and become common because myopia no longer confers a selective disadvantage—that's evolution! Moreover, infant and childhood mortality, while greatly reduced, is far from abolished even in industrial nations, and there, natural selection still has room to act—and, as you mention, anything that prevents reproduction is as bad as death, from an evolutionary perspective. Studies of population biology indicate that that very small differences in fitness—undetectably minuscule differences—can drive big changes over the long haul. Hence, we still have plenty of opportunity to evolve, despite our greatly extended lifespan.

It is fun to try to identify evolutionary forces in modern Western society. Teenage depression? Drunk driving? Inability to cope with noise pollution? A big problem in doing so is that our environment—which by now is largely a product of our own society—keeps changing so quickly. And, needless to say, the change is accelerating.

One can also argue that in the context of overpopulation, "voluntary" sterility (i.e., sterility when fertility is physiologically possible) confers a selective advantage, albeit a very indirect one, in that it can prevent a population from destroying itself through overconsumption. Definitely there are animal species whose fecundity diminishes after reaching a certain population density.

Actually, in your list of three requirements for evolutionary change, natural selection is not strictly required. If a population is very small, random chance will do the trick (i.e., genetic drift). Drift, however, is not likely to spur large changes in modern human populations, as mobile as most of us are.

Some very intriguing recent work has been done looking at genes that have undergone recent positive selection in humans. Many, like the lactase gene in Northern Europeans, have probably been favored by the advent of agriculture some twelve millenia past.




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