Humans don't use as much brainpower as we like to think

Public Release: 31-Oct-2017
Humans don't use as much brainpower as we like to think
Animals had energy-hungry brains long before we did
Duke University

For years, scientists assumed that humans devote a larger share of their daily calories to their brains than other animals. Although the human brain makes up only 2 percent of body weight, it consumes more than 25 percent of our baseline energy budget.

But a study published Oct. 31 in the Journal of Human Evolution comparing the relative brain costs of 22 species found that, when it comes to brainpower, humans aren't as exceptional as we like to think.

"We don't have a uniquely expensive brain," said study author Doug Boyer, assistant professor of evolutionary anthropology at Duke University. "This challenges a major dogma in human evolution studies."

•••••

As expected, the researchers found that humans allot proportionally more energy to their brains than rodents, Old World monkeys, and great apes such as orangutans and chimpanzees.

Relative to resting metabolic rate -- the total amount of calories an animal burns each day just to keep breathing, digesting and staying warm -- the human brain demands more than twice as many calories as the chimpanzee brain, and at least three to five times more calories than the brains of squirrels, mice and rabbits.

But other animals have hungry brains too.

In terms of relative brain cost, there appears to be little difference between a human and a pen-tailed treeshrew, for example.

Even the ring-tailed lemur and the tiny quarter-pound pygmy marmoset, the world's smallest monkey, devote as much of their body energy to their brains as we do.

"This shouldn't come as too much of a surprise," Boyer said. "The metabolic cost of a structure like the brain is mainly dependent on how big it is, and many animals have bigger brain-to-body mass ratios than humans."

•••••