CHANGING TRAITS

How we’ve changed over time. This week: our muscles have become weaker OVER the past six million years, the strength of human muscle has decreased.

But this isn’t due to our sedentary lifestyles — it is thought to be due to the energy needs of our brain. This theory emerged when scientists tested the comparative muscle strength of chimps and humans for a study published in PLoS Biology. They found the chimps were far stronger.

What they think has weakened human muscle is our metabolism, and scientists now believe that to evolve our bigger brain — which accounts for 20 per cent of our energy needs — our muscles had to use less energy and so became weaker.

Modern lifestyles have less impact. When scientists gave macaque monkeys little exercise, high stress and a poor diet for two months, it reduced their muscle strength by just 3 per cent.