Walking in the Trees or Knuckling Under?

An article in the journal Science 'Walking on Trees' by Paul O'Higgins and Sarah Elton (http://www.sciencemag.org/cgi/content/summary/316/5829/1292) suggests, largely on the basis of watching Orang-utans move around with straightened legs in trees, that bipedalism in our human ancestors may have developed before we left the canopy. They suggest that walking on branches with the arms free to gather food items was an effective lifestyle for our ancestors and, when the trees were replaced by savanna in Africa, the proto-humans were able to use these skills on the ground. This view is in direct contrast to the more established view that our early ancestors went through a knuckle-walking stage on the ground (like modern Chimpanzees and Gorillas) by bending their knees and getting additional balance from the arms. This is an intriguing suggestion but one should point out that the Orang-utan is more distant to the Human line than either Chimpanzees or Gorillas. In addition, Chimpanzees, Gorillas and Humans are the only primates to have 8 wrist bones rather than the more usual 9. It is generally argued that the 8 result from the fusion of 2 bones to provide more support when knuckle walking but this is not a conclusive argument.