Comment on "Origin of Human Bipedalism As an Adaptation for Locomotion on Flexible Branches"
Thorpe et al. (Reports, 1 June 2007, p. 1328) concluded that human bipedalism evolved from a type of bipedal posture they observed in extant orangutans with seemingly human like extended knees. However, humans share knuckle walking characters with African apes that are absent in orangutans. These are most parsimoniously explained by positing a knuckle walking precursor to human bipedalism.
Science