Can’t drink milk? Blame the cows, the genes and the ancestors rather than the gut.
After studying data from 270 African and Eurasian populations in 39 countries, Cornell University researchers have concluded that the ability to digest milk is hereditary, developing only among those whose distant relatives once tended dairy herds.
In America, the idea translates into numbers. The condition plays ethnic favorites: Up to 75 percent of blacks and American Indians, plus 90 percent of Asian-Americans are unable to digest lactose, a sugar in milk, according to the National Institutes of Health. Overall, 50 million Americans are considered lactose intolerant.
“This is a spectacular case of how cultural evolution—in this case, the domestication of cattle—has guided our biological evolution,” said Paul Sherman, a professor of neurobiology and behavior at Cornell. The findings will be published in upcoming issue of the journal Evolution and Human Behavior.
Adults who trace their roots to the cow-friendly climes of Europe developed the ability to digest milk—they literally “passed on gene mutations that maintain lactase into adulthood,” the research notes.
The researchers are mystified, though, by a dozen small groups in Africa and the Middle East who happily drank milk, though their neighbors could not.
“The most likely explanation is nomadism,” Mr. Sherman theorizes, noting that historically, the groups often kept small cattle herds and moved before some hidden disease pathogen could pose a threat to their cows.