Scientists at the University of Liverpool have found that humans ability to walk upright developed from ancestors foraging for food in forest tree tops and not from walking on all fours on open land.
It was traditionally thought that humans became upright walkers in a slow process which had its origins in knuckle-walking movement on all fours just as chimpanzees and gorillas walk today. It was believed that this developed once human ancestors moved out of the forests into the savannahs of East Africa.
Study at the University of Liverpool, in collaboration with the University of Birmingham, into the behaviour of the orang-utan, has now suggests that knuckle-walking evolved quite recently in chimpanzees and gorillas, as a way of moving on the forest floor, whilst walking on two legs assisted by the support of tree branches is an older trait and evolved from tree walking. The study suggests that walking on two legs was always a feature of great-ape behaviour and human ancestors never passed through a knuckle-walking phase.
Skeletons of early human ancestors show a combination of short legs and long arms, which are adaptations for moving amongst tree tops, with hindlimbs adapted for walking on two legs. To understand why bipedalism walking on two legs would be necessary for the tree-living ancestors of humans, scientists studied the movement of the only completely arboreal great ape, the Sumatran orang-utan. It appears that they use bipedalism to forage for food from small branches of tree tops, and to cross directly from tree top to tree top.
Professor Robin Crompton explains: We found that orang-utans walking bipedally on springy branches act much like athletes running on springy tracks; they use extended postures of knee and hip to give them straighter legs. Other recent work by the team shows that orang-utans use the natural springiness of branches to save energy in movement, especially when crossing from one
Contact: Samantha Martin
University of Liverpool