Researchers say cooking was commonplace among Homo erectus and probably originated early in their era or earlier

Early humans cooked up their first hot meals more than 1.9m years ago, long before our ancient ancestors left Africa to colonise the world, scientists claim.

Researchers at Harvard University traced the origins of cooking back through the human family tree after studying tooth sizes and the feeding behaviour of monkeys, apes and modern humans.

They concluded that cooking was commonplace among Homo erectus, our flat-faced, thick-browed forebears, and probably originated early in that species' reign, if not before in more primitive humans. "This is part of an emerging body of science that shows cooking itself is important for our biology; that is, we are biologically adapted for cooking food," said Chris Organ, an evolutionary biologist at Harvard.

The advent of cooking was one of the most crucial episodes in the human story, allowing our ancestors to broaden their diet and extract more calories from their food. Because it softened food, it also spelled an end to the days of endless chewing. There has been disagreement among experts on the issue. Some of the most convincing evidence for human use of fire is more recent, dating to around 400,000 years ago, though older claims exist, including the remnants of a campfire in Israel that dates back to 790,000 years ago.

The researchers began by creating an evolutionary tree of monkeys, apes and modern humans. On to this they added information on how long various species spent feeding. Compared with chimpanzees, our closest living relatives, humans spent remarkably little time eating. Chimps typically spent more than one third of their day feeding, while for humans it was about 5% of their waking hours.

The scientists then added information on tooth sizes to the family tree, and this time they included details of extinct human ancestors and closely related species.

The study showed that three species of humans, Homo erectus, Neanderthals (Homo neanderthalensis), and modern humans (Homo sapiens), evolved small molars relatively quickly, which could not be explained by general changes in head and jaw sizes.

Instead, the scientists believe the invention of cooking could explain the changes in both tooth size and feeding times. As early humans learned how to cook, they no longer needed large back teeth to chew tough food, or had to spend hours chewing to gain enough calories. Over time, large teeth disappeared from our ancestors, to be replaced with far smaller ones.

According their report in the US journal Proceedings of the National Academy of Sciences, Homo erectus, which emerged in Africa around 1.9m years ago, spent 6.1% of its time eating. Neanderthals, the authors claim, spent 7% of their time feeding. "We think that Homo erectus and Neanderthals were spending about as much of their day feeding as we do, which implies that they were both cooking," Organ said.

More primitive species, such as Homo habilis and Homo rudolfensis, which emerged before Homo erectus and the Neanderthals, spent 7.2% and 9.5% of their day eating. If the estimates are right, it suggests they may have been less accomplished cooks than Homo erectus and the Neanderthals.

The study lends support to an argument put forward by one of its co-authors, Richard Wrangham, another evolutionary biologist at Harvard, who claimed that harnessing fire to cook food was instrumental in the rise of modern man in his 2010 book Catching Fire: How Cooking Made Us Human.