Human Evolution Exchanged Brawn for Brains: Muscles and Smarts May be Intertwined

It turns out that humans may have exchanged their brawn for brains over the course of their evolution. Scientists have discovered that there are staggering differences between human muscles and the muscles of our closest living cousins, the chimpanzees.

Genomes accumulate changes over time, and among these genetic changes have been a few that have changed the course of human evolution. In fact, only a few might be responsible for the rise of distinct, human features. Yet other molecules have also played a role, which is why researchers decided to take a closer look at the evolution of metabolites, which are small molecules like sugars, vitamins, amino acids and neurotransmitters that represent key elements of our physiological functions.

"Metabolites are more dynamic than the genome and they can give us more information about what makes us human," said Philipp Khaitovich, one of the researchers, in a news release. "It is also commonly known that the human brain consumes way more energy than the brains of other species; we were curious to see which metabolic processes this involves."

In fact, the researchers found that unlike the uniformly-paced evolution of the genome, the metabolome of the human brain evolved four times faster than that of the chimpanzee. What was more surprising, though, was that the human muscle accumulated an even higher amount of metabolic change.

"For a long time we were confused by metabolic changes in human muscle until we realized that what other primates have in common, in contrast to humans, is their enormous muscle strength," said Kasia Bozek, one of the researchers, in a news release.

In fact, researchers found that chimpanzees and macaques can beat humans in a pulling strength competition by more than two-fold. This suggests that it's possible that the metabolic roles of human brain and brawn are intertwined.

"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," said Bozek in a news release.

The findings reveal that it's possible that these human-specific metabolic features could not only be related to physical or cognitive performance, but also to common human metabolic diseases. This could mean that future research may not only reveal more about human evolution, but could also pave the way for developing treatments to disease.

The findings are published in the journal PLOS Biology.