Survival of the Fattest

For all its recent fame, the thrifty gene hypothesis isn’t new. Geneticist James Neel of the University of Michigan Medical School proposed it in 1962 in the American Journal of Human Genetics. “It must be remembered,” he wrote, “that during the first 99 percent or more of man’s life on Earth, while he existed as a hunter and gatherer, it was often feast or famine.” The human who gorged and then held an extra pound or two in reserve when food was scarce was better able to survive. Thus, he concluded, the development of insulin resistance (a propensity for diabetes) conferred some physiological advantage that continues to exert itself.In the five decades since its debut, the theory has “gone off in all sorts of directions,” says Andrew Prentice, who studies international nutrition at the London School of Hygiene & Tropical Medicine. Prentice supports the general concept Neel proposed —  that the genetic influences on body weight are the product of natural selection from lean times — but not in the way people commonly interpret it. For one, he doesn’t think the advantage of fatness had much to do with mortality.