It turns out that humans walking on two legs use only one-quarter of the energy that chimpanzees use while knuckle-walking on four limbs. And the chimps, on average, use as much energy using two legs as they did when they used all four limbs.

• 测算结果表明，人类用两条腿行走时消耗的能量仅为大猩猩四肢着地行走时所消耗能量的四分之一。平均来看，大猩猩两条腿行走时消耗的能量与四肢着地行走时的差不多。