What makes humans so special?  Our big brains, of course, and (don’t tell the gym rat next to you) our weak physique. Or so say scientists in a new study published in PLOS Biology. Comparing the metabolism in different types of tissues in humans, chimpanzees, macaques, and mice, the team found that, sure, our brains evolved rapidly over the past millions of years, but so did our muscles.

In fact, while the metabolism of the human brain evolved four times faster than that of the chimpanzee, human muscle accumulated an even higher amount of metabolic change—ten times that of the chimpanzee. But while the changes in our brain—the prefrontal cortex region, to be exact—have made us smarter, the changes in our muscle “seem to be paralleled by a drastic reduction in muscle strength,” according to the study.

To confirm their thinking, the team ran two experiments. The first, meant to rule out our sedentary “couch potato” lifestyle as cause for the change in muscle metabolism, involved macaques. The monkeys were moved from a spacious countryside facility to small indoor enclosures and served fatty and sugary food for several weeks, to imitate the environment of many contemporary humans. These changes had only a fractional effect on the macaques’ muscle metabolism.

The second test pitted several chimpanzees, macaques, university basketball players, and mountain climbers in a pulling-strength competition. Despite their sweat and determination, all of the human participants of the experiment were outcompeted by their primate opponents by more than two-fold.

“Our results suggest a special energy management in humans, that allows us to spare energy for our extraordinary cognitive powers at a cost of weak muscle,” summarizes lead author Kasia Bozek of the Max Planck Institute.

Brains over brawn, I guess.

Image: Lin Mei/Wikipedia

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