Figure 2. A reconstruction of the arboreal bipedalism hypothesis depicting the evolution of modern great apes including humans from an orthograde ancestral ape, capable of hand-assisted, arboreal bipedalism with extended lower limbs (from O’Higgins & Elton 2007). Orangutan ancestors became arboreal specialists, whereas the ancestors of gorillas and chimpanzees, in response to changing and variable habitats, climbed vertically in and out of trees, and independently acquired knucklewalking. Hominins retained existing adaptations for extended-limb bipedalism and eventually became committed terrestrial bipeds. Reprinted with permission from AAAS.
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