A multinational team of researchers led by Dr Philipp Khaitovich from Planck Institute for Evolutionary Anthropology in Leipzig, Germany, has suggested that metabolic roles of human brain and brawn are intertwined.

Dr Khaitovich and his colleagues investigated the evolution of metabolites – small molecules like sugars, vitamins, amino acids and neurotransmitters that represent key elements of human physiological functions.

“Metabolites are more dynamic than the genome and they can give us more information about what makes us human. 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,” said Dr Khaitovich, who is the senior author of a paper published in the open-access journal PLoS Biology.

Indeed, it turned out that the metabolome of the human brain has evolved four times faster than that of our closest living cousin, the chimpanzee. What was more surprising, however, is that human muscle accumulated an even higher amount of metabolic change – 10 times that of the chimpanzee.

To rule out the possibility that this change simply reflects our couch potato lifestyle, Dr Khaitovich’s team performed additional measurements in specially treated macaque monkeys. These macaques 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 lifestyle changes had only a small effect on the macaque muscle metabolome.

“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 study first author Dr Kasia Bozek, also from Planck Institute for Evolutionary Anthropology.

Dr Josep Call from the Wolfgang Kohler Primate Research Center in Leipzig, a study co-author, added: “this is common knowledge to all the zoo keepers, but it was never tested systematically.”

To prove their point, the scientists involved several chimpanzees, macaques, university students, and even professional athletes 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,” Dr Bozek said.

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Bozek K et al. 2014. Exceptional Evolutionary Divergence of Human Muscle and Brain Metabolomes Parallels Human Cognitive and Physical Uniqueness. PLoS Biol 12 (5): e1001871; doi: 10.1371/journal.pbio.1001871