Scientists have discovered that humans walking on two legs use only a quarter of the energy that chimpanzees uses to walk on all fours. This further supports the theory that humans became bipedal to reduce energy costs:
“Walking upright on two legs is a defining feature that makes us human,” said study leader Herman Pontzer, an anthropologist at Washington University in St. Louis. “It distinguishes our entire lineage from all other apes.”
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. Recent studies have also suggested that, rather than taking millions of years to evolve from a hunched position as is commonly believed, our early ancestors were already capable of standing and walking upright the moment they descended from the trees.