Walking upright 'saved energy'

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 from the University of Arizona in Tucson 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 both using four legs and two legs on the moving platform.

Measurements showed that humans walking on two legs used on 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.

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.

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