THE French have elevated it to an art form, and even the British have got better at it 鈥� but chimps can鈥檛 cook at all. According to one controversial evolutionary theory, early humans developed a taste for cooked food around 2 million years ago, and this set in motion a series of changes that made us utterly different from any other animal.
Now the proponents of the cooked-food hypothesis are presenting fresh evidence in support of the idea 鈥� and it all comes down to how you chew.
The theory, championed by Richard Wrangham at Harvard University, has divided palaeoanthropologists. In an attempt to convince the doubters, Wrangham and his colleagues have been amassing empirical evidence, including evolutionary adaptations consistent with a diet of heated food, such as the small size of our guts.
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At the in Portland, Oregon, at the end of June, of Harvard and Brown University in Providence, Rhode Island, presented what he and Wrangham say is the best evidence yet that we are adapted to eating cooked food, and that this is the result of events that occurred early on in human evolution.
Organ and , also of Harvard, had predicted that if humans are uniquely adapted to eating cooked food, then we should spend far less time chewing than other primates, as cooked food tends to be softer than raw food. To test this, they gathered data from various primate species and looked at the correlation between chewing time and body size, taking into account how the different species were related to each other.
A primate species of our size should, in theory, spend 48 per cent of the waking day chewing, they found. Yet on average we chew for less than 10 per cent of the day, says Organ.
The pair then did a comparison of molar size and found that humans fall well outside the normal range for primates: we have small molars for our body size. When they included teeth from fossils of extinct hominins, the analysis revealed that Homo habilis and its contemporary H. rudolfensis fit well with the average for similarly sized primates. But Neanderthals and our direct ancestor, H. erectus, had small teeth for their body size.
鈥淗umans fall well outside the normal range for primates: we have small molars for our body size鈥�
This confirms what palaeoanthropologists have long known, says Leslie Aiello, president of the in New York. 鈥淚n H. erectus the molars are considerably smaller than in the earlier hominids,鈥� she says. 鈥淚t鈥檚 something that nobody has been able to explain.鈥�
For Wrangham, cooking is the explanation. Around 1.8 to 2 million years ago, he says, H. erectus or perhaps an immediate ancestor acquired a taste for food that had accidentally fallen into a fire. These early humans then learned to use fire for cooking, unwittingly getting more nourishment as a result.
Because the cell walls in cooked food are already partially broken down, it needs less chewing and is easier to digest. Wrangham argues the additional energy humans gained allowed them to evolve bigger brains and build complex social relationships. He points out that the fossil record suggests the size of hominin brains grew rapidly around this time.
Still, other explanations cannot be ruled out, such as a transition to meat-eating 1.5 to 2 million years ago. Although raw meat is hard to digest, early humans may have been able to extract more energy with less chewing if they had pounded the meat or focused on eating softer, richer tissues like the liver and heart.
The key stumbling block for the theory that our early ancestors cooked their food is that as yet there is no convincing evidence that hominins could control fire more than a million years ago. The oldest direct evidence for fire at a site of human habitation only goes back to 790,000 years ago at Gesher Benot Ya鈥檃gov in Israel, where charred flints, seeds and stone tools have been found, says of the Smithsonian Institution in Washington DC.
Aiello says that if Wrangham is right, cooking hearths would have had to be widespread around 1.5 to 2 million years ago, otherwise 鈥渋t would have been an 鈥榦h shit鈥� moment when the fire went out and our ancestors had to wait 10,000 years to get fire again,鈥� she says.
