The question posed by the title of Why Some Like It Hot: Food, Genes, and Cultural Diversity (Island Press, $24) doesn't produce a terribly interesting answer. To oversimplify, some (like author Gary Paul Nabhan himself) prefer their food hot because they have taste buds very different from those of other people (like one of Nabhan's hapless old flames -- their romance might have gone further if he had offered her flowers rather than a home-cooked meal.)

An ethnobiologist who heads the Center for Sustainable Environments at Northern Arizona University, Nabhan addresses fascinating issues: why half the world's population can tolerate lactose while the other half can't, why it's beneficial that teenage boys in Sardinia develop an anemia-like malaise every spring, why some ethnic groups have a predisposition to alcoholism, how genes can mutate due to changes in diet.

To explain how a culture's choice of food affects -- and is affected by -- its genetic characteristics, the author went to the highlands of Crete to sample the supposedly super-healthful Mediterranean diet. There Nabhan, winner of a MacArthur "genius" award in 1990, learned firsthand that many modern people just aren't equipped to digest so much olive oil.

Nabhan writes compassionately about indigenous groups -- like Native Americans and ethnic Hawaiians -- that are threatened by globalization. Our Fast Food Nation is overwhelming these cultures; just as important, it is jeopardizing their health. But for those of us whose genes have been stewing for generations in the American melting pot, what's the point?

One of the points is that we all should be wary of gene therapy, of genetically modified foods, of even the now-common fortification of foods with nutrients like folic acid. Although all of these interventions have real or promised benefits, such tinkering can be risky.

Nabhan's overall message is that while we are what we eat, we are also what our forebears ate, and that some don't like it hot because too much heat can be deadly. *

Tom Graham writes on science for The Washington Post.