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Thursday, January 03, 2008

Changing Your Mind: Are Humans Evolving?

Steven Pinker, a psychologist at Harvard University (USA) used to think that humans had stopped evolving. Now he's changed his mind ... [Have Humans Stopped Evolving?]
Ten years ago, I wrote:
For ninety-nine percent of human existence, people lived as foragers in small nomadic bands. Our brains are adapted to that long-vanished way of life, not to brand-new agricultural and industrial civilizations. They are not wired to cope with anonymous crowds, schooling, written language, government, police, courts, armies, modern medicine, formal social institutions, high technology, and other newcomers to the human experience.
Are we still evolving? Biologically, probably not much. Evolution has no momentum, so we will not turn into the creepy bloat-heads of science fiction. The modern human condition is not conducive to real evolution either. We infest the whole habitable and not-so-habitable earth, migrate at will, and zigzag from lifestyle to lifestyle. This makes us a nebulous, moving target for natural selection. If the species is evolving at all, it is happening too slowly and unpredictably for us to know the direction. (How the Mind Works)

New results from the labs of Jonathan Pritchard, Robert Moyzis, Pardis Sabeti, and others have suggested that thousands of genes, perhaps as much as ten percent of the human genome, have been under strong recent selection, and the selection may even have accelerated during the past several thousand years. The numbers are comparable to those for maize, which has been artificially selected beyond recognition during the past few millennia.

If these results hold up, and apply to psychologically relevant brain function (as opposed to disease resistance, skin color, and digestion, which we already know have evolved in recent millennia), then the field of evolutionary psychology might have to reconsider the simplifying assumption that biological evolution was pretty much over and done with 10-000 — 50,000 years ago.
I'm glad he's changed his mind but it's for the wrong reasons.

Evolution, human or otherwise, cannot ever be stopped. Pinker, like the true adaptationist he is, cannot conceive of any evolution mechanism other than natural selection. Even if his original writings were correct, all he said is that natural selection may have stopped. Evolution by random genetic drift—the most frequent form of evolution—never stops.

It's interesting to see Pinker make the connection between the presumed stoppage of human evolution after the shift from hunter-gatherer mode, and evolutionary psychology. I never really thought about it before but that connection is a basic assumption in most of the the just-so stories promoted by evolutionary psychologists. If there has been lots of recent selection in human populations then it becomes more difficult to attribute our current "primitive" behavior to old adaptations that took place 100,000 years ago.

[Photo Credit: CivilBrights]

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