Learning to cook may have helped the human brain grow, and may have led to the invention of tools, culture and civilization, scientists claim.

Getting enough energy for a large brain by eating nothing but raw food takes up too much time, leading researchers to suggest that the advent of cooking would have provided early humans a much more efficient way of delivering calories to neurons or brain cells to allow the brain to expand.

Researchers said that cooking would have meant fewer hours spent foraging for food and more time for social interaction and creative tasks, which probably contributed more the evolution of a larger and more complex brain, according to the study published Monday in the journal Proceedings Of The National Academy Of Sciences.

Brazilian scientists led by Suzana Herculano-Houzel, from the Federal University of Rio de Janeiro calculated and analyzed the metabolic requirements of both modern great apes and a range of different early human species.

Researchers found that large apes with energy-hungry bodies, like gorillas, have already reached the limit of achievable brain size with a raw-food diet. Gorillas spend about eight to ten hours a day eating. Researchers say that for a gorilla to have a brain that is as large as a human brain, or to correspond to 2 percent of its body mass, it must spend more than another two hours a day feeding.

Herculano-Houzel and her team say that their analysis suggests that three early human species, Homo habilis, Australopithecus afarensis and Paranthropus boise would have all needed to spend more than seven hours a day eating raw food to support their brain size.

They say that cooking was probably invented by the Homo erectus, a species that lived up to 1.8 million years ago and is believed to be a direct ancestor of modern humans.

"The advent of cooking food... greatly increases the caloric yield of the diet, as a result of the greater ease of chewing, digestion and absorption of foods," Herculano-Houzel and her team wrote in the study. "In line with this proposition, a cooked diet is preferred by extant (present day) non-human great apes."

"Although the earlier addition of raw meat to the diet of earlier hominins may also have contributed to increase its caloric content, raw meat is difficult to chew and ingest, whereas cooked meat is easier to chew and has a higher caloric yield," they added. "Cooking would have also increased the time available for social and more cognitively demanding activities."