Cooking raw food led to increased consumption of calories by humans, paving way for the excess energy to aid in brain development, claims a new study.
The study indicated that if human beings had not invented cooking as a way of increasing the number of calories they consumed, they could only have supported the 86bn neurons in their big brains by spending an impossible nine hours or more each day eating raw food, the Guardian reported.
The finding, the researchers suggested, explains why great apes such as gorillas, which can have bodies three times the size of humans, have considerably smaller brains.
Though gorillas typically spend up to eight hours feeding, their diet influenced an evolutionary tradeoff between body and brain size; supporting both big bodies and big brains would be impossible on a raw food diet.
The brain is so energy-hungry that in humans it represents 20 percent of the resting metabolic rate, even though it only represents 2 percent of body mass, suggested Professor Suzana Herculano-Houzel and Karina Fonseca-Azevedo of the Institute of Biomedical Sciences at the Federal University of Rio de Janeiro.
"Why are the largest primates not those endowed with the largest brains as well? Rather than evidence that humans are an exception among primates, we consider this disparity to be a clue that, in primate evolution, developing a very large body and a very large brain have been mutually excluding strategies, probably because of metabolic reasons," they said.
Gorillas, they suggest, already live on the limit of viability, foraging and eating for 8.8 hours a day, and in extreme conditions increasing this to as much as 10 hours a day.
In contrast, humans' move to a cooked diet, possibly first adopted by Homo erectus, and their bigger brains yet smaller bodies, left spare energy which allowed further rapid growth in brain size and the chance to develop the big brain as an asset rather than a liability, through expanded cognitive capacity, flexibility and complexity.
"We propose that this change from liability to asset made possible the rapid increase in brain size that characterises the evolution of Homo species, leading to ourselves. We may thus owe our vast cognitive abilities to the invention of cooking - which, to my knowledge, is by far the easiest and most obvious answer to the question, what can humans do that no other species does?" Herculano-Houzel said.
A paper describing their study was published in the journal PNAS, the Proceedings of the Natural Academy of Sciences of the USA.