(Four to seven million years ago, humans and chimpanzees diverged from a common ancestor. They then developed independently.) ... As a group, the humans used 75 percent less energy walking upright than the chimps used walking on all fours. Essentially, walking upright seemed to be beneficial because it saved energy.

When did humans start walking upright?

From at least 6 to 3 million years ago, early humans combined apelike and humanlike ways of moving around. Fossil bones like the ones you see here record a gradual transition from climbing trees to walking upright on a regular basis. Sahelanthropus may have walked on two legs.

Why did humans go upright?

According to this theory, the energy saved by walking upright gave our ancient ancestors an evolutionary advantage over other apes by reducing the costs of foraging for food. The idea is just one of many scientists have entertained as reasons for why humans walk on two legs.