We are the only species on earth that cooks its food - and we are also the cleverest species on the planet.The question is: do we cook because we're clever and imaginative, or are we clever and imaginative because our ancestors discovered cooking?Horizon examines the evidence that our ancestors' changing diet and their mastery of fire prompted anatomical and neurological changes that resulted in taking us out of the trees and into the kitchen.Homo habilis was about a metre tall with long, swinging arms - not much to look at, apparently, but clever. Habilis had a bigger brain (50% bigger) than his forebear, Australopithecus. Was this down to his diet?In Did Cooking Make Us Human?, a clutch of determined scientists set out to discover the extent to which diet played a role in the evolution of the human brain, using a variety of mildly alarming gadgets.Professor Peter Ungar has a contraption he calls the Bitemaster 2, a mechanical chewing machine he has fitted out with genuine Australopithecine gnashers.For the first time in three million years they were set to work on a carrot, with remarkable success, considering.On raw meat they performed less ably, but teeth from a later human ancestor - smaller, sharper, "crestier" - made short work of it.You certainly wouldn't want to get your finger caught in there, as Prof Ungar nearly does. "Wait!" he yells at his start-button-happy colleague.