Have humans traded brawn for brains?

Science : Whereas humans have evolved to have larger brains compared with other primates, they have become physically weaker. To better understand that apparent tradeoff, Philipp Khaitovich of the CAS-MPG Partner Institute for Computational Biology in Shanghai, China, and colleagues studied energy use in five different tissues of four animal species: humans, chimps, rhesus monkeys, and mice. In comparing metabolic and genetic differences among the species, the researchers found that the only significant evolutionary change was in the human brain in the prefrontal cortex, which appears to have evolved much faster than that of the other species. Because the researchers found little structural difference between chimp and human thigh muscle, however, they concluded that the difference in strength between the two species must lie in energy use. They propose that energy resources were reallocated in humans, such that they developed bigger brains at the expense of weaker muscles. However, a counterargument has been made that humans have simply become more energy efficient by using their brains to enhance survival by becoming more effective hunters, learning to cook food, and sharing food with others.