Fast Metabolism Gave Humans Bigger Brains

May 6, 2016 | Erica Tennenhouse

Comparison of different primate skulls
Photo credit: Christopher Walsh (CC BY 2.5)

Our internal engines are revved up!

The human brain consumes more energy than any other organ. All that thinking requires fuel. Luckily, humans are able to produce plenty — thanks to our high metabolic rates.

In a study published in the journal Nature, humans were shown to have higher metabolic rates than our primate relatives, which might explain why humans were able to evolve such large brains.

Adjusted for body size, on a daily basis humans were found to consume 400 more calories than chimpanzees and bonobos, 635 more calories than gorillas, and 820 more calories than orangutans.

Total energy expenditure was then measured in each species using a technique called doubly labeled water, which is the best way to measure the carbon dioxide we expel as we burn energy. The researchers found that humans burned calories at a rate 27 percent faster than the other species.

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Big brains are just one of several energy-intensive traits that evolved in the human lineage. Humans also reproduce more often than other apes and have longer lifespans.

“It has been an open question — how do we do all these expensive things?” said biological anthropologist Herman Pontzer of Hunter College in New York City, lead author of the new study, to Science News.

This research shows that it is a boosted metabolism that enables humans to perform all of these energetically costly functions.

The researchers also found that humans also have a high percentage of body fat. They noted that humans appear to have evolved a predisposition to deposit fat, whereas other apes — even those in captivity — are lean.

“The fat is your reserve tank to help fuel this metabolic engine that we have revved up compared to the other apes,” Pontzer told The Guardian.

Next, the researchers will try to determine how and when the metabolism of our ancestors started to take off by analyzing rates of bone growth in fossils.

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