Did cooking help grow the human brain?

The cooking hypothesis, associated with Harvard anthropologist Richard Wrangham, holds that our ancestors began cooking food well over a million years ago, and that this supplied the extra energy needed to support a larger brain. Cooking softens food and increases the calories the body can extract from it. Wrangham places the change around 1.8 million years ago, with the appearance of Homo erectus. Many specialists accept that cooking matters for modern humans but doubt it explains the early timing. [1] [2]

The brain needs more energy for its size than any other organ, and Wrangham says it consumes about a quarter of the body's energy. Cooking is proposed as a way of paying that cost. It makes eating faster and easier, and it begins digestion outside the body by breaking down muscle and plant cells. Starchy tubers, for example, are barely digestible raw. Wrangham argues that this let the gut shrink, so energy that once supported a large gut could go to the brain instead. [3] [1] [4] [2]

Modern humans appear to depend on cooking. Up to 50 percent of women who eat only raw food develop amenorrhea, a sign of too little energy to support a pregnancy. [3]

Wrangham points to Homo erectus, which appeared roughly 1.6 to 1.9 million years ago. Its brain was 50 percent larger than that of H. habilis, and it showed the largest drop in tooth size in human evolution. Its jaws, teeth and guts were smaller while its brain and body were larger, which fits a softer, richer diet. Supporters add that traces of purposeful fire at Wonderwerk Cave in South Africa are more than a million years old, that some genetic adaptations to cooked food may predate the split from Neandertals, and that chimpanzees show a preference for cooked food and the planning skills cooking would need. [2] [3] [1]

The main objection is archaeological. Evidence for controlled fire and hearths is sparse before about 500,000 years ago, and the Harvard Gazette notes that firm evidence of fire and cooking goes back only about 800,000 years. Some researchers think cooking began at most 500,000 years ago. C. Loring Brace noted that earth-oven cooking by Neandertals goes back only a couple hundred thousand years. Wrangham's defenders reply that the archaeological record grows more fragile with age, so absence of evidence is weak. [2] [3] [1]

A second objection is that other diets could explain the change. The expensive tissue hypothesis of Leslie Aiello and Peter Wheeler also links smaller guts to bigger brains, but credits energy-dense animal foods such as bone marrow and brain tissue. Brace and others likewise favor soft animal products. Wrangham responds that meat-eating theories do not account for the smaller jaws and teeth of H. erectus. Open questions include how much came from cooking versus pounding or cutting food. The Scientific American reporting says most researchers remain skeptical without regular evidence of fire at H. erectus sites. [2] [1] [3]