Evolving brain and brawn

Although our closest relatives are chimps, in evolutionary terms, we're still very different from our ape cousins. And in a paper in the journal PLoS Biology, scientists from Shanghai and Germany have discovered that these differences may have evolved quickly over time in two key tissues - our brain and brawn, or rather, muscle.

Humans and chimps split from our last common ancestor around 7 million years ago, and it might be expected that both species have evolved at roughly the same pace since then. But rather than focusing on changes in DNA, the scientists looked at the evolution of metabolites - small molecules like sugars, vitamins and the building blocks of proteins, called amino acids.

They found that metabolite levels changed rapidly over the course of human evolution in two tissues: brain and muscle. It turns out that human metabolite levels in the brain have evolved four times faster than that of the chimps, while the change in muscle has been ten times faster.

But while this may have improved our brains, it's been at the expense of our brawn - in pulling competitions, the researchers found that humans were easily beaten by chimps and macaque monkeys. It looks like our impressive brainpower may have come at the cost of our muscle-power - perhaps you can only have brains or brawn, but not both.