December 10, 2006

Recent Natural Selection in Humans

A Nicholas Wade piece in the New York Times reports that two mutations for lactose tolerance in human adults arose in East Africa as recently as 3,000 years ago. The ability of adults to digest milk conferred a tremendous adaptive advantage among cattle herders. The mutations prevent the gene from being switched off after weaning. A different mutation with similar effects is found in northwest Europe, where a cattle-based agricultural economy also became dominant.

Aside from its intrinsic interest, this development raises the question--what other selective pressures, other than cattle domestication, have given rise to genetic changes in human populations? Are the tribes and regions that abound in excellent distance runners subject to selective pressures? In societies that reward scholars and test-takers, such as some Jewish groups and the Chinese Empire, does skill at book-learnin' confer a selective advantage? Did the Middle Passage, from Africa to American slavery, confer selective advantages on certain traits? If evolutionary change can be this rapid, lactose tolerance is unlikely to be an anomalous exception.

To consider seriously these important questions, we will have to give up our prudishness about inherited differences between populations.

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