video: This video depicts an adult female Sumatran Orangutan walking upright in the Gunung Leuser National Park, Indonesia. By analyzing the movement of wild orangutans, which spend most of their lives in trees, Susannah Thorpe and colleagues found that upright walking while using arms for balance, or "hand-assisted bipedalism," may have offered our arboreal ancestors several advantages for navigating trees' thin, flexible branches. Their observations, "Origin of Human Bipedalism As an Adaptation for Locomotion on Flexible Branches," appeared in the June 1, 2007, issue of the journal Science published by AAAS. view more
Credit: Video courtesy SKS Thorpe via <i>Science</i>-AAAS