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Is human evolution over? Nah.

Posted in Rationally Speaking by Skepdude on October 17, 2008

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A recent article in the Times (of London) quotes Steve Jones, a renowned geneticist author of Darwin’s Ghost (nothing less than an updated version of Darwin’s Origin of Species), as saying “Human evolution is over. Quite unexpectedly, we have dropped the human mutation rate because of a change in reproductive patterns.” What’s he talking about?

Jones maintains that older men (35+) contribute most of the new mutations entering the human gene pool, and those people ain’t reproducing as they used to. Really? Perhaps Jones has forgotten that for most of human history people were highly unlikely to live to, let alone reproduce, at that old age (by Pleistocene standards). Besides, what are we to make of cultural trends (in Western societies) that postpone reproduction for both men and women?

Well, Jones says, “In the old days, you would find one powerful man having hundreds of children,” citing the example of Moulay Ismail from 18th century Morocco who (allegedly) copulated with an average of 1.2 women per day for a straight 60 years (without Viagra), thereby producing a whopping 888 children (nicely symmetric number, which probably doesn’t take into account the human tendency for exaggeration and the likely fact that some of Ismail’s concubines were having, shall we say, side jobs). At any rate, these “old days” are just not old enough to be evolutionarily relevant. The appropriate time frame, again, is pre-agricultural time, when most of human evolution took place. And in those old days there simply wasn’t enough food to go around for a single man to maintain dozens of sexual partners and their offspring.

“In ancient times” continues Jones in the Times interview, “half our children could have died by the age of 20. Now, in the Western world, 98 per cent of them are surviving to 21.” The key words here, of course, are “in the Western world,” as infant and child mortality (and hence the opportunity for natural selection to do its work) are still astronomically high outside of Western societies (and a few others, like Japan). Besides, here is an area where I’m going to be glad that natural selection has a little less wiggle room than it would have without modern medicine.

Finally, Jones complains that human populations have become too large (certainly true from the point of view of our environmental impact) and interbreed too much (I will refrain from engaging in ethnic jokes by pointing out that only a Brit could complain about too much sex. Oh, darn, I just did engage in an ethnic joke). The problem here is that this reduces the relevance of the chance factor in evolution, which is associated with random fluctuations in gene frequencies in very small populations. But human populations have probably very rarely been small enough for so-called genetic drift to have a major effect, and Jones seems to be forgetting that the flip side of that coin is that large populations carry more genetic variation, and are thereby better suited to respond to selection.

As for the last comment in the published interview: “History is made in bed, but nowadays the beds are getting closer together. We are mixing into a global mass, and the future is brown.” As in: we will all look the same, because biologically based ethnic differences will be erased by worldwide interbreeding. Well, to begin with, this is just not happening quickly enough for my taste. Talk about a truly color-blind society that would result from it! Second, I’m sure the human ability to arbitrarily define in-group and out-group membership, thereby continuing the self-destructive “us-vs-them” attitude that has characterized us since “the old days” isn’t going to be halted by a simple quirk of demography.

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