Nicholas Wade, a leading science writer whose specialty is human evolution, likes to ask interesting questions. Here are some examples:

Why has the West been the most exploratory and innovative civilization in the world for the past 500 years?

Why are Jews of European descent so massively overrepresented among the top achievers in the arts and sciences?

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Why is the Chinese diaspora successful all around the world?

Why is it so difficult to modernize tribal societies?

Why has economic development been so slow in Africa?

Contemporary thinkers have offered lots of provocative answers for such questions. It's all about geography. Or institutions. Or rice culture. Or the devastating legacy of colonialism. Or Jewish mothers. Now comes another explanation, one that bravely explores the highly dangerous elephant in the room. Mr. Wade argues that human history has also been profoundly influenced by genetics.

Part of his new book, A Troublesome Inheritance: Genes, Race and Human History, is a summary of new findings in genetic science, and part of it is highly speculative. All of it is bound to be deeply unpopular among social scientists, because it challenges their entrenched belief that race is nothing more than a social construct. The wide diversity in human societies around the world can be explained entirely by culture, they insist. We're all the same under the skin.

Except we're not quite. Since the sequencing of the human genome in 2003, evidence of subtle genetic differences has been piling up. As our ancestors branched out of Africa, different groups of people evolved in slightly different ways to adapt to local conditions. The most successful of those people passed on their adaptations to their offspring. The variations in human DNA correspond quite precisely to what we think of as the major races. They are associated not just with differences in hair and skin colour, but also with a range of other physical and (probably) behavioural traits. Another astonishing fact is that 14 per cent of the human genome has been under natural selection strong enough to be detectable. The evidence also shows that evolution can proceed remarkably quickly, and has never stopped. (The Tibetan adaptation to high altitudes is just 3,000 years old.) "Human evolution has been recent, copious and regional," Mr. Wade says in his book.

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.

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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. "If the differences between a tribal society and a modern state were purely cultural," he writes, "it should be easy to modernize a tribal society by importing Western institutions." But tribal societies are characterized by strong kinship relations and low levels of trust toward non-kin. Western institutions are characterized by high levels of trust among strangers. Tribal institutions are designed to empower the officeholder and his tribe, while Western institutions are designed to operate in the public interest. These differences are far more than skin deep, and have been shaped by centuries of human evolution.

The genetic basis for traits such as trust, conformity and aggression is still opaque. But Mr. Wade is convinced that it was rapid evolution of human nature in England and Northern Europe that paved the way for the ascendance of the West. (This highly original theory was developed by economic historian Gregory Clark in his book A Farewell to Alms.) For a variety of reasons, including brutal population pressures, people developed a cluster of traits – nonviolence, literacy, thrift and patience – that gradually became the values of society as a whole. "The ability of the rich to raise more surviving children slowly diffused the social behaviours required for modern prosperity into the wider society," Mr. Wade says. These behaviours became the fertile soil for the Industrial Revolution, which vaulted Britain out of its Malthusian poverty trap and paved the way for Western domination: "The rise of the West is an event not just in history but also in human evolution."

Mr. Wade is quite careful to reject notions of "superiority" and "inferiority" when discussing population variations. People adapted to the circumstances in which they found themselves, and shaped their institutions accordingly. "Different," he stresses, does not mean "better."

Even so, you can be sure that quite a lot of people do not want to have this conversation, or even admit that it might be legitimate. They do not want to entertain the thought that genetics could be a reason why human societies differ. Sure, they believe in evolution – except when it comes to us.