National Geographic : 2014 Sep
50 national geographic • september 2014 Africa, popularized the image of our early ances- tors hunting meat to survive on the African sa- vanna. Writing in the 1950s, he described those humans as “carnivorous creatures, that seized living quarries by violence, battered them to death... slaking their ravenous thirst with the hot blood of victims and greedily devouring livid writhing flesh.” Eating meat is thought by some scientists to have been crucial to the evolution of our an- cestors’ larger brains about two million years ago. By starting to eat calorie-dense meat and marrow instead of the low-quality plant diet of apes, our direct ancestor, Homo erectus, took in enough extra energy at each meal to help fuel a bigger brain. Digesting a higher quality diet and less bulky plant fiber would have allowed these humans to have much smaller guts. The energy freed up as a result of smaller guts could be used by the greedy brain, according to Leslie Aiello, who first proposed the idea with paleo- anthropologist Peter Wheeler. The brain requires 20 percent of a human’s energy when resting; by comparison, an ape’s brain requires only 8 percent. This means that from the time of H. erectus, the human body has depended on a diet of energy-dense food—especially meat. Fast-forward a couple of million years to when the human diet took another major turn with the invention of agriculture. The domesti- cation of grains such as sorghum, barley, wheat, corn, and rice created a plentiful and predictable food supply, allowing farmers’ wives to bear ba- bies in rapid succession—one every 2.5 years in- stead of one every 3.5 years for hunter-gatherers. A population explosion followed; before long, farmers outnumbered foragers. Over the past decade anthropologists have is driving the current craze for Paleolithic diets. The popularity of these so-called caveman or Stone Age diets is based on the idea that modern humans evolved to eat the way hunter-gatherers did during the Paleolithic—the period from about 2.6 million years ago to the start of the ag- ricultural revolution—and that our genes haven’t had enough time to adapt to farmed foods. A Stone Age diet “is the one and only diet that ideally fits our genetic makeup,” writes Loren Cordain, an evolutionary nutritionist at Colorado State University, in his book The Paleo Diet: Lose Weight and Get Healthy by Eat- ing the Foods You Were Designed to Eat. After studying the diets of living hunter-gatherers and concluding that 73 percent of these societies derived more than half their calories from meat, Cordain came up with his own Paleo prescrip- tion: Eat plenty of lean meat and fish but not dairy products, beans, or cereal grains—foods introduced into our diet after the invention of cooking and agriculture. Paleo-diet advocates like Cordain say that if we stick to the foods our hunter-gatherer ancestors once ate, we can avoid the diseases of civilization, such as heart disease, high blood pressure, diabetes, cancer, even acne. That sounds appealing. But is it true that we all evolved to eat a meat-centric diet? Both pale- ontologists studying the fossils of our ancestors and anthropologists documenting the diets of indigenous people today say the picture is a bit more complicated. The popular embrace of a Paleo diet, Ungar and others point out, is based on a stew of misconceptions. MEAT HAS PLAYED a starring role in the evolution of the human diet. Raymond Dart, who in 1924 discovered the first fossil of a human ancestor in The popularity of so-called Stone Age diets is based on the idea that modern humans evolved to eat the way hunter-gatherers did during the Paleolithic period.