Sir David was wrong

Another in the ongoing project to archive posts from an old blog – this one from february 2009.

Not in the television programme — well, I don’t know, I haven’t seen it yet due to pesky tennis fans capturing the remote control — but in the Simon Mayo interview (page liable to expire, but I guess everyone has heard the podcast). The statement to which I refer, made by David Attenborough on Radio 5 on Friday, concerns that old question of whether human evolution has “stopped”. A lot of people like to comment on this issue, and I can see why. It’s a quirky question that does not appear to be of great consequence, but which appeals to our collective ego; and it’s a question that has an obvious answer. Obviously evolution has stopped: advances in agriculture, medicine, and technology mean that we are no longer subject to natural selection pressures. As Sir D puts it, “the Darwinian survival of the fittest has now been largely negated.”

Trouble is, the obvious answer is wrong. It would be correct if we redefined evolution to fit a definition of “fittest” as being adaptation to a pre -agrarian culture. But that is not what evolution means. Lets take the oft-quoted definition of evolution as “change in allele frequencies over time” — that is, gene variants becoming more or less common in a population. Now think about it: humans have been taken from their previous hunter-gatherer niche — where evolution would be stabilising good hunter-gatherer adaptations in the population — and put into a whole different niche, where many hunter-gatherer adaptations are superfluous, or even unhelpful. Under such circumstances, you can bet that some allele frequencies are changing. Stabilising selection has been lifted, and now genetic drift and mutation of those genes can occur freely, eroding the now superfluous adaptations.

There are several reasons why this error is so attractive. I suppose it comes from viewing evolution as a progressive process striving for perfection. Evolution and natural selection are seen as being about creating new adaptations, and one forgets the roles of genetic drift, and stabilising selection. Certainly, if one can’t see the creation of something new and interesting and obviously adaptive, it’s easy to overlook the fact that evolution is happening all the same. If an improvement to a body part becomes more common in a population, we instantly recognise evolution; but we don’t recognise evolution in the loss of such a feature, or the gain of a genetic disorder. I’m sure Sir David is aware of all of this, but it’s easy to lapse into popular but wrong ways of thinking — we’ve all done it.

But on the question of whether humans are evolving, there’s a second reason why the error is not easily forgiven. It is always asserted that the reason for human evolution having stopped is that technological, agricultural, and medical advances have put an end to famine, pestilence, infant mortality, and the other natural selection pressures. And, however many times I have heard the claim, I still haven’t gotten over the astonishment that such a bad argument can be made by such great intellects. If the claim were true, what conclusions can we draw about evolution in the population of Zimbabwe, where famine is setting in, HIV/AIDS has halved life expectancy to the early thirties, and infant mortality is one in ten? The simple fact is that the human species does not have advanced agriculture, technology, and medicine.

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