Modern life may have solved most of our food-gathering problems, but human evolution has not kept up. Our bodies are still wired for hunter-gatherer biology: Eat all the food you can and store it — in body fat — in case your supply of food runs out, as in the case of famine. A dangerous configuration for a society with all-you-can-eat buffets. And modern taste combinations like concentrated fat (butter) and concentrated sweetness (sugar) rarely co-exist in nature, notes Loren Cordain, professor of health and exercise science at Colorado State University. Cordain argues that when it comes to food, evolutionary mechanisms simply can't match the fast pace of human innovation. "What I think we can say conclusively, is that the evolutionary success of our species is ultimately a nutrition story," says Bill Leonard, chairman of Northwestern University's anthropology department. One crucial step forward, he says, came with the development of the brain of Homo erectus about 1.5 million years ago. Leonard analyzed the brain sizes of human ancestors and found they started growing rapidly with the first human species, Homo habilis, about 2 million years ago. About 600 cubic centimeters, the Homo habilis brain was far larger than the brains of earlier australopithecine species. Then, between 2 million and 1.5 million years ago, brain size quickly grew to 900 cubic centimeters, surpassing modern apes' brains. That's an important change because larger brains require more energy. According to a 2003 article by Leonard, Homo erectus devoted 17 percent of calories to its brain; chimps use about 9 percent. We modern humans use nearly a quarter of our resting energy on our brains. Shrinking stomachs are another piece of the evolutionary puzzle. Homo erectus appears to have had a smaller gut than its predecessors, with a stomach and intestine that grew more compact as higher-quality foods became available. Better foods meant more calories for less work, an evolutionary step favoring hominids that could hunt meat and collect more nutritious plants. A high caloric intake isn't so much to blame as an imbalance between calories in and calories out. Though developing nations generally consume fewer calories than industrialized nations, Leonard found subsistence societies that match developed societies calorie for calorie. The reindeer-herding Evenki people of Siberia consume more than 2,800 calories a day, and far more animal foods than the typical American, yet have lower cholesterol and body mass indicators. Peter Stearns believes nothing short of "an adverse evolutionary consequence" — drastically shorter life spans, or perhaps a hampered ability to reproduce — will force large-scale behavioral changes. http://www.msnbc.msn.com/id/7270028/
