The pyramids, art, all of the world's great inventions, literary works, just about any valuable intellectual work can be traced back to food - cooked food. If you care to go as far back as our very roots, that is. Previous research showed that cooked food made it easier and more efficient for our guts to absorb calories more rapidly, which helped increase the brains of our early ancestors. A new research by neuroscientists at the Federal University of Rio de Janeiro in Brazil found that humans nowadays would need to eat 9 hours non-stop to get enough energy from unprocessed raw food alone to support our large brains.
"If you eat only raw food, there are not enough hours in the day to get enough calories to build such a large brain," says Suzana Herculano-Houzel, a neuroscientist at the Federal University of Rio de Janeiro in Brazil who is co-author of the report. "We can afford more neurons, thanks to cooking."
Humans have roughly three times as many neurons (86 billion) than our close primate cousins, like gorillas (33 billion) or chimpanzees (28 billion). The Brazilian scientists found that the number of neurons is directly linked to brain size, as well as to the amount of energy needed to feed the brain. Thus, humans need brains consume 20% of our body's energy when resting, compared with 9% in other primates - a hefty cost. This begged the question, however: from where did our ancestors get all this extra energy to grow such a large brain in a relatively short evolutionary time frame?
The answer is cooked food, according to the researchers. Back in the 1990s, Harvard University primatologist Richard Wrangham asserted, in a now famous thesis, that the human lineage embarked on an explosive growth of the brain some 1.6 to 1.8 million years ago when Homo Erectus started cooking food. Wrangham claimed that processed food is more efficiently absorbed in the body, significantly increasing the relative energy intake compared to digesting raw food. Follow-up studies at the time demonstrated that rodents or pythons grow faster and bigger when they eat cooked meat instead of raw meat, and that it takes less energy to digest cooked meat than raw meat.
You'd need to eat raw food for 9 hours without rest in order to get the same energy kick
For the present research, the neuroscientists calculated how many hours per day humans and other primates need to eat raw food in order to support their current brains and body size. They found that it would take 8.8 hours for gorillas; 7.8 hours for orangutans; 7.3 hours for chimps; and 9.3 hours for our species, H. sapiens. Worth noting is the fact that raw food in this case, refers to that found in the wild, not processed raw food that humans typically prepare with blenders and add protein and other nutrients to.
"The reason we have more neurons than any other animal alive is that cooking allowed this qualitative change—this step increase in brain size," she says. "By cooking, we managed to circumvent the limitation of how much we can eat in a day."
This study shows "that an ape could not achieve a brain as big as in recent humans while maintaining a typical ape diet," Wrangham says.
Not all researchers are convinced however that cooking food sparked the brain growth explosion of our ancestors. That may very well be so, believes Paleoanthropologist Robert Martin of The Field Museum in Chicago, Illinois, who agrees that the present paper is the first to provide tangible evidence of metabolic limitations, but who goes on to say that whether our ancestors began cooking over a fire later, when the brain went through a second major growth spurt about 600,000 years ago or during H. Erectus is still unclear. The earliest evidence of hominid fire control found thus far has been dated from 800,000 years ago, and regular use of fire for cooking doesn't become widespread until more recently.
"Gorillas are stuck with this limitation of how much they can eat in a day; orangutans are stuck there; H. erectuswould be stuck there if they had not invented cooking," Herculano-Houzel said. "The more I think about it, the more I bow to my kitchen. It's the reason we are here."
Findings were published in the journal Proceedings of the National Academy of Sciences.