Animal, Vegetable, Miracle_ A Year of Food Life - Barbara Kingsolver [71]
This is not an allergy or even, technically, a disorder. Physical anthropologists tell us that age four, when lactose intolerance typically starts, is about when nature intended for our kind to be wholly weaned onto solid food; in other words, a gradual cessation of milk digestion is normal. In all other mammals the milk-digesting enzyme shuts down soon after weaning. So when people refer to this as an illness, I’m inclined to point out we L.I.’s can very well digest the sugars in grown-up human foods like fruits and vegetables, thank you, we just can’t nurse. From a cow. Okay?
But there is no animal weirder than Homo sapiens. Over thousands of years of history, a few isolated populations developed intimate relationships with their domestic animals and a genetic mutation gave them a peculiar new adaptation: they kept their lactose-digesting enzymes past childhood. Geneticists have confirmed that milk-drinking adults are the exception to the norm, identifying a deviant gene on the second chromo-some that causes lactase persistence. (The gene is SNP C/T13910, if you care.) This relatively recent mutation occurred about ten thousand years ago, soon after humans began to domesticate milk-producing animals. The gene rapidly increased in these herding populations because of the unique advantage it conferred, allowing them to breast-feed for life from another species.
The gene for lifelong lactose digestion has an 86 percent frequency among northern Europeans. By contrast, it shows up in only about one-third of southern Europeans, who historically were not big herders. In the Far East, where dairy cattle were unknown, the gene is absent. Even now, Southeast Asians have virtually zero tolerance for lactose. Only about 10 percent of Asian Americans can digest milk as adults, along with fewer than half of American Jews and about a quarter of rural Mexicans. Among Native Americans it’s sketchily documented—estimates range from 20 to 40 percent. Among African Americans, adult milk-drinking tolerance is high, nearly 50 percent, owing to another interesting piece of human history. The mutation for lactase persistence emerged several times independently, alongside the behavior of adult milk-drinking. It shows up in populations that have little else in common other than cows: the tall, lean Fulani of West Africa; the Khoi pastoralists of southern Africa; and the fair-skinned Northern Europeans.
And then, to make a long story short, one of those populations proceeded to take over the world. If that’s a debatable contention, let’s just say they’ve gotten their hands on most of the planet’s billboards and commercials. And so, whether or not we were born with the La Leche for Life gene, we’re all hailed with a steady song and dance about how we ought to be drinking tall glasses of it every day. And we believe it, we want those strong bones and teeth. Oh, how we try to behave like baby cows. Physicians will tell you, the great majority of lactose-intolerant Americans don’t even know it. They just keep drinking milk, and having stomachaches.
White though we are, my redheaded elder daughter and me, some sturdy, swarthy gene has come down through the generations to remind us that “white” is relative. We’re lactose intolerant. But still, like most everyone else, we include some dairy products in our diet. I can’t blame dairy-industry propaganda, purely, for our behavior. The milk of mammals is a miraculously whole food for the babes it was meant to nourish; it’s the secret of success for the sheep, oxen, bison, kangaroos, seals, elephants, whales, and other mammals that have populated every corner of the blue-green world with their kind and their suckling young. For the rest of us it’s a tempting source of protein, calcium, minerals, and wholesome fats.