Thursday, October 22, 2015
Over the past few years, I have noticed that gluten, a protein present
in wheat, has received lots of media attention. As with other food
fears, I have mostly ignored the journalists and, as usual, it appears
that the media tide is about to turn. Most of the arguments I have
heard about gluten have been based on an incomplete understanding of
evolution and genetics, as a recent
piece in the New York Times does a good job
Wheat was first domesticated in southeastern Anatolia perhaps 11,000 years ago. (An archaeological site in Israel, called Ohalo II, indicates that people have eaten wild grains, like barley and wheat, for much longer -- about 23,000 years.)The piece goes on to also examine why genes leading to gluten intolerance are even as common as they are, and summarizes an interesting real-life, Berlin Wall-like "experiment" that suggests these genes offered an evolutionary advantage to humans, at least until more recently.
Is this enough time to adapt? To answer that question, consider how some populations have adapted to milk consumption. We can digest lactose, a sugar in milk, as infants, but many stop producing the enzyme that breaks it down -- called lactase -- in adulthood. For these "lactose intolerant" people, drinking milk can cause bloating and diarrhea. To cope, milk-drinking populations have evolved a trait called "lactase persistence": the lactase gene stays active into adulthood, allowing them to digest milk.
Milk-producing animals were first domesticated about the same time as wheat in the Middle East. As the custom of dairying spread, so did lactase persistence. What surprises scientists today, though, is just how recently, and how completely, that trait has spread in some populations. Few Scandinavian hunter-gatherers living 5,400 years ago had lactase persistence genes, for example. Today, most Scandinavians do.
Here's the lesson: Adaptation to a new food stuff can occur quickly -- in a few millenniums in this case. So if it happened with milk, why not with wheat?
"If eating wheat was so bad for us, it's hard to imagine that populations that ate it would have tolerated it for 10,000 years," Sarah A. Tishkoff, a geneticist at the University of Pennsylvania who studies lactase persistence, told me.
Interestingly, the article suggests that "diseases of civilization" may well occur -- but with environmental changes on a much shorter time scale than the purveyors of that idea that I have seen usually claim.