ACCUMULATION OF SMALL ADVANTAGES. Book Review No. 31, some good on-train reading, is Gary Nabhan's Why Some Like it Hot. In some places it reads like a young adult's diary; in some places the knowledge of blood chemistry and related topics is a bit beyond me. The central thesis is straightforward enough, "[W]e are what our ancestors ate, and also what they had to regurgitate," and in some ways the findings parallel some of the observations in Guns, Germs, and Steel about technology transfers. In this case the frontier between Eurasia and the rest of the world is in the South Pacific, where the plants of Java are familiar to those observed on Eurasia; go a few islands east and the plants are completely different. The cautions are also instructive: no magic genetic marker for difficulties eating some foods; both rapid and slow adaptations are observable in people and other species. (Note: differences in adaptation rates cannot be seized upon as refutations of evolution or as evidence of intelligent design. It takes an improved theory to beat a moderately successful theory.)

But think about how populations with similar genetic codes and different resource endowments might reward mutations differently. That's the main story of the book. Consider foragers. A mother nursing a child is less effective as a forager. An enzyme that turns off a baby's desire to suckle favors faster weaning, and greater fertility in the mother, something else that might be favored with lots of infant mortality and short life expectancies. Now consider herders. That enzyme will not be as favored in a population that has learned to make yogurt and cheese and later used the milk directly. On the other hand, herders might learn to develop substitutes for water, particularly water downstream from the pasture. Here another enzyme that aids the digestion of fermented liquids might be favorably selected. Over the years, a population with a longer history of foraging might be more lactose-intolerant and alcohol-intolerant than a population with a longer history of herding.

There are several other case studies in this vein that, taken together, suggest proposing a single dietary fix for all earthlings subject to obesity or heart disease or cancers is nearly impossible. But for a population with common traditions and less intermarriage outside the extended family, there are health gains to respecting the ancient traditions. Mr Nabhan has an intriguing way of summarizing it.

When the persistence of traditional foods is more widely recognized as a source of both cultural pride and as an aid to physical survival and well-being, I doubt that many Native American communities will abandon what many of them feel to be a true gift from their Creator.

I also discovered that my willingness to help out my younger siblings with their brussels sprouts and cauliflower and my later affinity for hot peppers are connected.