Theory that the primates evolved by adapting to life high up in the trees, where visual abilities would have been favored over the sense of smell, and grasping hands and feet would have been used for movement among branches. Changes in the visual apparatus were adaptive in the trees, where depth perception facilitated leaping. Grasping hands and feet were used to crawl along slender branches, as well as to anchor the body while the primate searched for food at the ends of the branches.