Walking with orangutans described in news@nature, ScienceNOW, BBC News and New Scientist, 31 May 2007. A group of British scientists have spent a year observing the way orangutans move around the trees of Gunung Leuser National Park in Sumatra, Indonesia. The researchers observed that orang-utans walk on all fours when on large branches with a diameter of more the 20cm, but on thinner braches they walk upright using their arms to support their weight by grasping other branches. When moving about like this they straightened their legs at the knees and hips in a similar way to humans. The ability to move over thinner branches like this makes it easier to move from tree to tree and to find fruit, which is usually found on the ends of thinner branches.

Robin Crompton of the University of Liverpool, UK who took part in the study commented, “Walking upright and balancing themselves by holding branches with their hands is an effective way of moving on smaller branches. It helps explain how early human ancestors learnt to walk upright while living in trees, and how they would have used this way of moving when they left the trees for a life on the ground.”Orangutans are believed to be the most distant from humans on the Great Ape evolutionary tree, but apes that are closer to us, i.e. chimps and gorillas, cannot walk with their legs extended. The British researchers suggest that humans and orangutans inherited the ability to walk upright from a tree-dwelling common ancestor of all apes and humans, and chimps and gorillas lost it. Crompton said to New Scientist there is fossil evidence suggesting bipedalism (upright two legged walking) evolved earlier than previously believed and it would explain why “the orangutan is the only ape with a knee joint similar to that of humans.”

Not all scientists agree with this theory. Anthropologist Daniel Lieberman of Harvard University in Cambridge, Massachusetts commented to news@nature, “This is a good argument for why upright posture would be selected for in trees,” but he goes on to say “Unless knuckle-walking evolved independently in both the chimpanzee and gorilla lineages, the evolution of bipedalism from an orang-like form of arboreal assisted bipedalism seems unlikely”.

BBC, New Scientist

Editorial Comment: The fact that orangutans can walk upright in trees means nothing more than they are well designed to live in forests, climb and walk in trees where their long arms prevent falling as they safely pluck fruit. Human beings are well designed to walk on the ground, having short arms so they easily fall out of trees and therefore don’t walk on thin branches to find food. Any who try are naturally selected against and eliminated from the population. The idea that humans inherited upright walking from a common ancestor to orangutans is blind faith as no-one has seen any other creature evolve to or from an organutan or a human being. (Ref. gait, anthropology, great-apes)

Evidence News 13 June 2007