Walking upright an evolutionary step to save energy, study finds

WALKING upright evolved in humans because it is the most energy-efficient way of getting around, new research suggests.

Chimpanzees and other apes tend to walk using both their feet and the knuckles of their hands.

But at some stage during the course of human evolution a critical switch was made to bipedalism.

Walking on two legs is regarded as a defining characteristic that marks the difference between humans and apes.

Why this change happened has been a hot topic of debate for decades. The new research indicates that a key reason was that bipedalism saved energy.

Scientists in the US studied four adult humans and five chimpanzees walking on a treadmill. The chimps were trained to walk using both four legs and two legs on the moving platform.

Measurements showed that walking humans used only a quarter of the energy needed by knuckle-walking chimpanzees.

Generally, chimps used the same amount of energy on two legs as they did on four legs.

However, the energy they expended varied according to their gaits and anatomy.

For some chimps, bipedal walking was more efficient.

Dr David Raichlen of the University of Arizona said: “We were able to tie the energetic cost in chimps to their anatomy. We were able to show exactly why certain individuals were able to walk bipedally more cheaply than others, and we did that with biomechanical modelling.”

The findings, published in the journal Proceedings of the

National Academy of Sciences, showed that more energy was used with shorter steps.

The chimpanzee that was most efficient when walking upright was the one with the longest stride.

“What those results allowed us to do was to look at the fossil record and see whether fossil hominins show adaptations that would have reduced bipedal energy expenditures,” said Dr Raichlen.

He added that adaptations, such as slight increases in hind limb extension or length, in early hominins indicated energetics “played a pretty large role in the evolution of bipedalism.”