Compared to many other species in the animal kingdom, human muscles are relatively weak. A team of researchers have delved into the evolutionary mechanisms that have caused humans to prioritize brain development over pure muscle power.

While humans are almost certainly one of the smartest species to have ever walked the planet, Homo sapiens may have paid a steep price for all of that added brain power. While humans are more intelligent than other animals, they have weaker muscles. New research conducted by scientists from the Chinese Academy of Sciences (CAS) in Shanghai shows that all of the energy put into brain development may have led to decreased development in human musculature. The researchers published their findings in the online journal PLOS Biology.

To conduct the study, the researchers tried to identify the specific molecules that were involved in the natural selection of specific features unique to humans. This led the researchers to take a close look at the evolution of the human metabolome. The metabolome refers to the entire range of small molecules or metabolites that can be found in an organism.

"Metabolites are more dynamic than the genome and they can give us more information about what makes us human," said CAS researcher Philipp Khaitovich. "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."

The human brain is widely recognized as the most powerful and efficient computer known to man. However, all of this power uses up a significant percentage of the energy made available by the metabolism of the human body. All in all, the brain uses of approximately 20 percent of the energy in the human body. All of this energy goes into powering close to 100 billion neurons. This computing power means that not as much energy can be used for powering muscles.

"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 lead author Kasia Bozek from the CAS. "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."

The team's findings have lead the scientists to conclude the in terms of evolution, humans picked brains over brawn. While the scientists involved in the study say that the conclusion is far from certain, it is also the simplest explanation that can be given for the metabolic changes undergone by early humans. The researchers are also confident that their findings could lead to further investigations into metabolic properties that are unique to humans.