PARIS - Chimpanzees and humans share some of the basic brain skills needed for cooking, a finding that may explain a turning point in the story of mankind, a study said Wednesday.

Experiments at a chimp sanctuary suggest a common ancestor imparted these cognitive abilities to apes and humans alike, it said.

If so, it sheds light on how we came to cook -- an activity so banal that we have lost sight of its importance.

Using heat to break down tough fibres and starch, making meat and tubers easier to digest, broadened the diet of our hominid ancestors.

It provided the calorie boost that in turn led to the evolution of bigger, energy-hungry brains.

But when and how did humans acquire this skill?

A pair of scientists from Harvard and Yale believe the clue lies in Pan troglodytes -- chimpanzees, our closest living relative since our common ancestor split into ape and hominid lineages some 13 million years ago.

Many capacities for cooking "are thought to be uniquely human," said Alexandra Rosati, a Yale psychologist. "That's why we wanted to study this in chimpanzees."

Rosati and Felix Warneken of Harvard reported on experiments with two dozen wild-born chimps at the Tchimpounga Sanctuary in the Republic of Congo.

Their work appears in the journal Proceedings B of the Royal Society, Britain's de-facto academy of sciences.

In the first test, scientists placed a slice of sweet potato in a hot pan, without butter or oil, and offered it to the chimps alongside a raw sample.

The chimps vastly preferred cooked potato, they established.

The next step was to probe whether the animals understood how the food transformation worked.

For this, the team used a fake "cooking device" -- a plastic container with a false bottom concealing a piece of cooked potato.

A slice of raw potato was placed in the top, the lid replaced and the container shaken in front of the chimps before a cooked piece was removed from the secret chamber and offered to them.

There were also other, clearly distinguishable containers that did not "transform" the food when shaken.

After the demonstration, the chimps could choose between the two types of containers, not knowing their contents -- and opted for the "cooking device" more often than not.

The next experiment was even more telling.

- 'Genius' -

Given a piece of raw potato on one end of an enclosure, the chimps could choose to eat it right away or carry it to the opposite side, four metres (15 feet) away, to have it "cooked" in one of the devices.

"The first time one of the chimps did this, I was just amazed. I really had not anticipated it," Rosati said in a statement.

"When one of them did it, we thought maybe this one chimp is just a genius, but eventually about half of them did it."

To further test the chimps, the team gave them raw carrot. Without having been shown the "cooking" process with carrot, the chimps nevertheless opted to place them in the devices.

But when given a raw potato and a piece of wood, they only placed the food in the container, clearly demonstrating they knew what the "cooker" was all about, said the team.

Chimpanzees do not, of course, cook.

The animals have not mastered fire, their diet is different from ours and as a rule they do not share their food, whereas humans prepare meals for friends, families and others.

What chimps do have, though, is the same basic cognitive toolkit for cooking, according to the researchers.

Evidence that a common ape-like ancestor gave us these skills may provide insight into another significant event: when humans mastered fire.

A common theory is that hominins -- the primate group that includes the forerunners of modern humans -- learned how to control fire for defence or warmth, later using it for cooking.

In fact, cooking may have been a motivation to master fire, not a consequence of it, said the team.

"The evidence from our cognitive studies suggests that, even before controlling fire, early hominins understood its benefits and could reason about the outcomes of putting food on fire," said Rosati.