SURVEY: HUMAN EVOLUTION
Dec 20th 2005
From The Economist print edition
Evolution is still continuing
WHAT, then, of the future? Sitting in the comfort of the concrete savannah, has humanity stopped evolving?
To help answer that question, it is instructive to look at a paper published earlier this year by Gregory Cochran. Dr Cochran, a scientist who, in the tradition of Darwin himself, works independently of an academic institution, looked at the unusual neurological illnesses commonly suffered by Ashkenazi Jews. Traditional wisdom has it that these diseases, which are caused by faulty genes, are a consequence of inbreeding in a small, closed population. The fact that they persist is said to show that human evolution has stopped in our ever more mollycoddled and medicalised world. Dr Cochran begged not only to differ, but to draw precisely the opposite conclusion. He sees these diseases as evidence of very recent evolution.
Until a century or two ago, the Ashkenazim—the Jews of Europe—were often restricted by local laws to professions such as banking, which happened to require high intelligence. This is the sort of culturally created pressure that might drive one of Dr Deacon's feedback loops for mental abilities (though it must be said that Dr Deacon himself is sceptical about this example). Dr Cochran, however, suspects that this is exactly what happened. He thinks the changes in the brain brought about by the genes in question will be shown to enhance intelligence when only one copy of a given disease gene is present (you generally need two copies, one from each parent, to suffer the adverse symptoms). Indeed, in the case of Gaucher's disease, which is not necessarily lethal, there is evidence that sufferers are more intelligent than average. If Ashkenazi Jews need to be more intelligent than others, such genes will spread, even if they sometimes cause disease.
The fact is, you can't stop evolution. Those who argue the opposite, pointing to the survival thanks to modern medicine of people who would previously have died, are guilty of more than just gross insensitivity. They have tumbled into an intellectual pitfall that has claimed many victims since Darwin first published his theory. Evolution is not about progress. It is about adaptation. Sometimes adaptation and progress are the same. Sometimes they are the opposite. (Ask a tapeworm, which has “degenerated” into a mere egg-laying machine by a very successful process of adaptation.) If a mutation provides a better adaptation, as Dr Cochran thinks these disease genes did in financiers, it will spread. Given the changes that humanity has created in its own habitat, it seems unlikely that natural selection has come to a halt. If Dr Deacon is right, it may even be accelerating as cultural change speeds up, although the current rapid growth in the human population will disguise that for a while, because selection works best in a static population.
The next big thing
Evolution, then, has not stopped. Indeed, it might be about to get an artificial helping hand in the form of genetic engineering. For the fallacy of evolutionary progress has deep psychological roots, and those roots lie in Dr Miller's peacock-tail version of events. The ultimate driver of sexual selection is the need to produce offspring who will be better than the competition, and will thus be selected by desirable sexual partners. Parents know what traits are required. They include high intelligence and a handful of physical characteristics, some of which are universal and some of which vary according to race. That is why, once the idea of eliminating disease genes has been aired, every popular discussion on genetic engineering and cloning seems to get bogged down in intelligence, height and (in the West) fair hair and blue eyes.
This search for genetic perfection has an old and dishonourable history, of course, starting with the eugenic movement of the 19th century and ending in the Nazi concentration camps of the 20th, where millions of the confrčres of Dr Cochran's subjects were sent to their deaths. With luck, the self-knowledge that understanding humanity's evolution brings will help avert such perversions in the future. And if genetic engineering can be done in a way that does not harm the recipient, it would not make sense to ban it in a liberal society. But the impulse behind it will not go away because, progressive or not, it is certainly adaptive. Theodosius Dobzhansky, one of the founders of genetics, once said that “nothing in biology makes sense except in the light of evolution”. And that is true even of humanity's desire to take control of the process itself.