Mr. Wade knows he may be stepping on a land mine. In the not so distant past, ideas about racial difference have been used to justify everything from slavery to extermination. A lot of people think it’s safer to deny such differences exist. The subject is so taboo that any discussion of racial differences is widely considered tantamount to racism itself. Geographer Jared Diamond (author of Guns, Germs and Steel, which contends that geography explains everything) has said that only people capable of thinking the Earth is flat believe in the existence of human races. So that makes Mr. Wade, who has written for The New York Times for 20 years, either foolhardy or fearless. “The idea that human populations are genetically different from one another has been actively ignored by academics and policy makers for fear that such inquiry might promote racism,” he writes.

Mr. Wade argues that people the world over are highly similar as individuals. But because of slight but significant evolutionary differences in social behaviour, societies differ widely. The various components of social behaviour are no more exempt from natural selection than hair or skin colour – and are profoundly more critical to human survival. As people migrated out of Africa, this evolution in social behaviour proceeded independently in different parts of the world and shaped many different types of institutions.

This thesis has a certain powerful explanatory force. It helps explain why less successful cultures don’t simply copy more successful ones.