Science has a fascinating review about the history of cooking and its relation to human evolution. Richard Wrangham, a Harvard primatologist, has been pushing the idea that the expansion in Homo erectus‘ skull size was the result of additional energy released by cooking meat:
What spurred this dramatic growth in the H. erectus skull? Meat, according to a longstanding body of evidence. The first stone tools appear at Gona in Ethiopia about 2.7 million years ago, along with evidence that hominids were using them to butcher scavenged carcasses and extract marrow from bones. But big changes don’t appear in human anatomy until more than 1 million years later, when a 1.6-million-year-old skull of H. erectus shows it was twice the size of an australopithecine’s skull, says paleoanthropologist Alan Walker of Pennsylvania State University in State College. At about that time, archaeological sites show that H. erectus was moving carcasses to campsites for further butchering and sharing; its teeth, jaws, and guts all got smaller. The traditional explanation is that H. erectus was a better hunter and scavenger and ate more raw meat than its small-brained ancestors.
But a diet of wildebeest tartare and antelope sashimi alone isn’t enough to account for these dramatic changes, says Wrangham. He notes that H. erectus had small teeth–smaller than those of its ancestors–unlike other carnivores that adapted to eating raw meat by increasing tooth size. He argues that whereas earlier ancestors ate raw meat, H. erectus must have been roasting it, with root vegetables on the side or as a fallback when hunters didn’t bring home the bacon. “Cooking produces soft, energy-rich foods,” he says.
To find support for his ideas, Wrangham went to the lab to quantify the nutritional impact of cooking. He found almost nothing in food science literature and began to collaborate with physiologist Stephen Secor of the University of Alabama, Tuscaloosa, who studies digestive physiology and metabolism in amphibians and reptiles. Secor’s team fed 24 Burmese pythons one of four diets consisting of the same number of calories of beef: cooked ground beef, cooked intact beef, raw ground beef, or raw intact beef. Then they estimated the energy the snakes consumed before, during, and after they digested the meat, by measuring the declining oxygen content in their metabolic chambers. Pythons fed cooked beef spent 12.7% less energy digesting it and 23.4% less energy if the meat was both cooked and ground. “By eating cooked meat, less energy is expended on digestion; therefore, more energy can be used for other activities and growth,” says Secor.
Secor also helped Wrangham and graduate student Rachel Carmody design a pilot study in which they found that mice raised on cooked meat gained 29% more weight than mice fed raw meat over 5 weeks. The mice eating cooked food were also 4% longer on average, according to preliminary results. Mice that ate raw chow weighed less even though they consumed more calories than those fed cooked food. “The energetic consequences of eating cooked meat are very high,” says Wrangham. (Emphasis mine.)
Wrangham’s argument is controversial, however. There is a problem of timing with respect to when human ancestors developed fire. Most evidence suggests that they did not have fire nearly as early as Wrangham is suggesting:
Wrangham’s synthesis of nutritional, archaeological, and primatological data adds up to a provocative hypothesis that hot cuisine fueled the brain. “It’s such a nice explanation,” says paleoanthropologist Leslie Aiello, president of the Wenner-Gren Foundation in New York City. She says the smaller teeth in H. erectus indicate to her that it wasn’t chewing much tough raw food: “Something must be going on. If only there were evidence for fire.”
And that’s the stumbling block to Wrangham’s theories: Cooking requires fire. Irrefutable evidence of habitual cooking requires stone hearths or even clay cooking vessels. Solid evidence for hearths, with stones or bones encircling patches of dark ground or ash, has been found no earlier than 250,000 years ago in several sites in southern Europe. Charred bones, stones, ash, and charcoal 300,000 to 500,000 years ago at sites in Hungary, Germany, and France have also been assigned to hearths. And burned flints, seeds, and wood found in a hearthlike pattern have been cited as signs of controlled fire 790,000 years ago in Israel (Science, 30 April 2004, p. 725).
But even the earliest of those dates are long after the dramatic anatomical changes seen in H. erectus, says Wrangham. He notes that evidence for fire is often ambiguous and argues that humans were roasting meat and tubers around the campfire as early as 1.9 million years ago.
Indeed, there are a dozen claims for campfires almost that ancient. At the same meeting, paleoanthropologist Jack Harris of Rutgers University in New Brunswick, New Jersey, presented evidence of burned stone tools 1.5 million years ago at Olduvai Gorge in Tanzania and at Koobi Fora in Kenya, along with burned clay. H. erectus has been found at both sites. Claims by other researchers include animal bones burned at high temperatures 1.5 million years ago at Swartkrans, South Africa, and clay burnt at high temperatures 1.4 million years ago in the Baringo basin of Kenya.
But where there is smoke there isn’t necessarily cooking fire: None of these teams can rule out beyond a doubt that the charring comes from natural fires, although Harris argues that cooking fires burn hot at 600° to 800°C and leave a trail different from that of bush fires, which often burn as low as 100°C. (Emphasis mine.)
Oh, and by the way. I had always suspected that raw foodists were full of it. Now I know why.