Generally when you think about what separates humans from other species, features like upright walking, large brains and language come to mind.
But diet has actually played an enormous role in human evolution. Today at the annual meeting of the American Association for the Advancement of Science, a panel of anthropologists, geneticists and paleontologists got together to discuss how who we are has been shaped by what we eat.
Perhaps the most surprising conclusion was that — despite what some diet gurus may say — there is no “natural” human diet. Not only can humans thrive on a wide variety of diets, from the highly carnivorous fare of nomadic Siberians to the virtually all-potato menu consumed by native Peruvians, but thanks to evolution our species can change its diet surprisingly readily.
“You can find humans living well and healthily from a tremendous diversity of diets,” said William Leonard, an anthropologist at Northwestern University in Evanston, Ill.
But all cultures have one dietary feature in common, said Harvard University primatologist Richard Wrangham — they cook their food. Wrangham believes the advent of cooking during human prehistory was a major evolutionary milestone, because it essentially pre-digested starches and proteins and softened food, helping increase the amount of energy that could be extracted on it. In fact, he pointed out that people in modern technological societies who take up so-called “raw food” diets usually lose substantial amounts of weight.
Many diet books advise following a high-protein, low-carbohydrate diet in order to emulate the eating habits of pre-agricultural humans. Whatever the benefits of such a diet, however, it is clear that in the 10,000 years since the development of farming our genes have responded to the increasing availability of foods such as rice, grains and milk.
“I would say most people who descend from agricultural populations are actually pretty well adapted to a starch diet, because most of the world eats a lot of rice, a lot of corn and a lot of potatoes, said Anne Stone, a geneticist at Arizona State University.
Stone and her colleagues have studied the gene AMY1, which encodes a salivary protein called amylase that breaks down starch. All people have multiple copies of the AMY1 genes. But those from traditionally agricultural populations, such as the Japanese and Europeans, have many more than those from cultures that have never practiced agriculture.
Customers of 23andMe may be able to see the evolutionary effects of an agricultural heritage in their own genetic data. Before people started herding cattle, goats and sheep, the human biological machinery for digesting milk was turned off not long after infancy — perhaps to prevent older children from getting in destructive fights over breast milk. But with herd animals on the scene, when a genetic modification that kept milk digestion functioning into adulthood arose in Europe around 8,000 years ago, it was so beneficial that it eventually spread throughout the continent.
23andMe customers have one modified version of the lactase gene for each A at the SNP rs4988235.
Similar scenarios happened in several other parts of the world as well, so that now many people of European and some of African ancestry can easily digest large amounts of milk.