Why Do Humans Have Such Big Brains?

Humans have some of the biggest brains and it's not only for problem solving. Why we have big brains might just surprise you...

As a species, we humans have big brains. There's just no disputing this. In terms of weight ratios, relative to other animals, our brains are ridiculously plus-sized. But why are they so big?

Well, check out the big brain on Jules Suzdaltsev -- he's got some answers in today's DNews dispatch.

The go-to thought on this, for many years, was that human brains are bigger because we're so much smarter than other animals. After all, who invented the subprime mortgage? OK, bad example. But the point remains that humans have higher cognitive abilities than other species. So far as we know.

Alas, the correlation between brain size and intelligence just isn't there. Elephants and whales have bigger brains than us, for instance. Also, our big brain is something of a disadvantage, in terms of efficiency. Although the brain makes up about two percent of body mass, it takes up 20 percent of our blood and oxygen. That's more than twice the amount of other primates.

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One line of thought, called the energy trade-off hypothesis, proposes that humans developed larger brains at the expense of muscle mass. Researchers looked at changes in genes that transport glucose, an important energy source, and found that -- in comparison to chimps and orangutans -- human genes tend to provide energy to the brain over the muscles.

As to why we evolved bigger brains to begin with, it may well be a kind of sideways biological peer pressure. The social brain hypothesis holds that friendships, social relationships, and other complex interactions may hold the key to our big brain mystery. According to this school of thought, thinking about people -- keeping track of who is doing what to whom and why and how we fit into those relationships -- takes a ridiculous amount of processing power.

That's why the brain tends to burn through resources and, in time, grow bigger. Our brain's preoccupation with social matters isn't just neurotic musing, either. If you're good at interpersonal relationships, you're likely to have more sex, and if you're having more sex, the species propagates. Like everything else on the planet, it all comes down to evolutionary advantage.

Check out Jules' report for more information, including details on a recent study concerning skull fossils, parasites and the social brain hypothesis. Science marches on.

-- Glenn McDonald

Learn More:

Live Science: Why Are Human Brains So Big?

National Library Of Medicine: A Potential Role For Glucose Transporters In The Evolution Of Human Brain Size

Stanford University: Ask A Neuroscientist: Does A Bigger Brain Make You Smarter