Evolution and humans:big brain size and food supply (Evolution)

by David Turell @, Wednesday, June 21, 2017, 01:50 (277 days ago) @ David Turell

This article poo poos the social brain idea for enlargement:


"In the past two million years, humans have experienced a massive increase in brain size, one not seen in any other species. This rapid evolution gave us brains roughly triple the volume of those of our pre-human ancestors.

"But the intelligence we enjoy as a result would seem to be advantageous for all sorts of species, not just us. So why was ours the only line to go down this route?

"The social brain hypothesis was a popular answer. It claims that bigger brains and advanced cognitive abilities are primarily an adaptation to social complexities, with natural selection strongly favouring individuals that can outsmart rivals.

"Some researchers, myself included, have never been especially persuaded by this idea, which gains its principal support from decades-old evidence that primates in bigger groups have larger brains. Large brains in humans supposedly followed from our ancestors living in relatively large groups, according to this argument.

"A new study now challenges the foundational evidence for this link. The problem is that traditional analyses have been based on too few species, says a team at New York University (NYU).

"The researchers collected measures of primate brains and sociality from more than 140 primate species, about three times as many as before, and found no correlation between indicators of brain size and measures of sociality such as group size.

"Their statistics look strong. The social brain hypothesis has failed its biggest test so far.

"Proponents of the social brain hypothesis will doubtless seek ways to resuscitate it, but for the moment the question of why humans gained big brains needs another kind of answer.

"The NYU team offers one. They found that among primates, brain volume is correlated with diet, with fruit-eating primates having the biggest brains. This idea, raised decades ago but long overshadowed by the social brain hypothesis, raises two complementary possibilities.

"First is the idea that brainy individuals are better foragers. Fruits are hard to find in a tropical forest, and so bigger-brained individuals might benefit if they are smart enough to find fruit more efficiently. That is plausible – but suspiciously simple.

"The other explanation for fruit-eaters having big brains is the energy allocation hypothesis. It takes an entirely different approach, noting that brains need a lot of energy. Every primate would have a bigger brain if only they could afford them, metabolically speaking, it suggests.

"The human brain consumes more than a fifth of the energy we use when at rest. If some other organ is not to be under-supplied, we need to acquire more energy for our size than other species.

"How, then, can we afford to divert fuel to especially big brains? High-quality diets provide one mechanism. Fruits, being sugar-rich, supply more easily digested energy than most items eaten by primates, such as leaves.

"This concept appeals to those, like me, who think that a diet of cooked food has been a critical influence on human evolution ever since the emergence of Homo erectus almost two million years ago. Cooked food provides easily available energy, requires little digestion, can be eaten in a fraction of the time it takes to consume raw food, and is unique to humans.

"The evidence that fruit-eating primates are big-brained strengthens the idea that our unique cognitive ability was made possible by our uniquely high-quality diets.:

Comment: the obvious corollary is if you have a big enough brain to control fire, you can nourish that big brain so it works properly. See my entry yesterday: Tuesday, June 20, 2017, 00:36 . Once again, big brain first, use second.

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