The team recorded 10,000 different metabolites in each kind of tissue. They found that the metabolome profile for the human prefrontal cortex was strikingly different from those of other primates, and appeared to have evolved four times as fast as that of chimpanzees in the 6 million years since the two lineages split. The metabolome profile of human muscle had evolved more than eight times as fast as that of chimps in that same time.
The researchers then conducted strength tests of humans and the primates. “According to our results, an average adult chimpanzee is approximately two to three times stronger than an average adult human,” Khaitovich told Live Science. The researchers concluded that humans likely gave up muscle strength in order to route more energy the brain.
Other researchers, like Daniel Lieberman, an evolutionary biologist at Harvard, don’t agree with the team’s conclusions. Lieberman told The New York Times that he found the research “very cool,” but suggested that early humans evolved to be excellent runners and long-distance walkers. Such abilities allowed humans to gather more food to power bigger brains, he noted. “It may be that the human brain is bigger not in spite of brawn but rather because of brawn, albeit a very different kind,” Lieberman told the Times.