National Geographic : 2006 Jul
U) 0 0* w wS)c) 0) 134 NATIONAL GEOGRAPHIC * JULY 2006 Was walking on two legs an energy-saving measure for our ancestors? To help scientists fathom the answer, a trained, ten-year-old chimpanzee named Louie ambles willingly on a treadmill, first on two legs, and then on all four, his more usual "knuckle-walking" gait. The loose-fitting flow through mask captures his exhalations, which scientists analyze to measure energy expenditure. White dots on his joints convey to cameras the location and movement of his limbs in space. By revealing the amount of energy Louie expends with each step and how it's used, such experi ments may shed light on the energetics of our chimplike forebears-and whether ener gy economy was a likely cata lyst for their shift to bipedalism several million years ago.