orillas, of course, dwarf your average human. To fuel their massive bodies, the hulking primates spend as many as 10 hours of their day eating. If our close ape relatives spend so much time adding fuel to their bodies, scientists have wondered, why are our brains so much larger than theirs? A new study published in the Proceedings of the National Academy of Sciences might have an answer: Cooked food.
"Brains demand exceptional amounts of energy," says Ed Yong at Discover Magazine — energy that raw food simply can't provide. That's where cooking comes in.
Our ancestors overcame this constraint when they learned how to cook. Cooked food offers more calories than raw food, and is easier to chew and digest. These early chefs could gain more energy from the same amount of eating time. That, in turn, fueled more neurons and larger brains.
In fact, humans house more neurons in their noggins than any other primate, about 86 billion on average. By comparison, gorillas' brains have just 33 billion neurons, while chimps boast just 28 billion. There is a downside to our cognitive superiority, however: The human brain consumes "20 percent of our body's energy when resting, compared with 9 percent in other primates," says Anny Gibbons at Science Now.
To understand the role that cooking plays, researchers at the National Institute of Translational Neuroscience in Brazil studied 13 species of primates (including us) and, after counting the number of neurons in their brains in relation to their relative body mass, calculated how much raw food would be needed for their brains to stay fueled. For gorillas that'd be 8.8 hours; 7.8 hours for orangutans; 7.3 hours for chimps; and 9.3 hours for humans.
In other words: To fuel our brains, we'd have to spend the entirety of our 8-hour workdays (and then some) munching on raw food.
But researchers think that early man got an important evolutionary brain boost when, 800,000 years ago, hearths began showing up in humankind's archeological record. "We propose that this... made possible the rapid increase in brain size that characterizes the evolution of Homo species, leading to ourselves," says study author Suzana Herculano-Houzel. After all, "[cooking] is by far the easiest and most obvious answer to the question, what can humans do that no other species does?"
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