Chew on this: thank cooking for your big brain

THE French have elevated it to an art form, and even the British have got better at it - but chimps can't 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 - 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.

At the Evolution 2010 conference in Portland, Oregon, at the end of June, Christopher Organ 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.

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Bonobos have a secret

In the 1920s Robert Yerkes acquired an unusual ape that he named Prince Chim. Chim was more intelligent, fun-loving, cooperative, emotionally positive and full of life than his chimpanzee companion, Panzee. Chim's vocal behaviour was so prolific and reminiscent of language that Yerkes transcribed it using musical notation. Yerkes had discovered the bonobo.

In the 80s and 90s researchers conducted a study comparing a chimp and a bonobo. The aim was to determine if Yerkes's observations were accurate and if either animal, or both, could learn a human language through cultural immersion rather than instruction. The answer for both apes was yes.

Vanessa Woods writes engagingly of her husband, primatologist Brian Hare, struggling to tackle these questions again. Seemingly ignorant of the earlier work, in 2005 Hare embarked on a mission to find out what differentiates bonobos from chimps. With the Democratic Republic of Congo still mired in the aftermath of war, he travelled to the Lola Ya sanctuary in Kinshasa to study bonobos.

Hare found that bonobos do all kinds of things that chimps are not reported to do: they experience constant genital arousal, become attached to individual humans, think up new ways to engage in sexual, altruistic or cooperative behaviour on an essentially non-stop basis, and they die of broken hearts. In short they are a lot like people, even uncomfortably so - a fact that, ironically, has caused many scientists to ignore them.

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