Bipedalism: Orangutan to Human

New field observations of orangutans in Sumatra has shown that they walk on two legs just as much as humans do. Anthropologist Susannah K.S. Thorpe of the University of Birmingham in England and her colleagues, have found that these bipedalist have been at it for more than 20 million years ago.

Investigators have assumed for so long that an upright stance is unique to hominids, but studies have suggested otherwise. The unique trait being a skeletal smoking gun that supposedly separated members of our evolutionary family from other ancient primates. Two-legged walking was and is thought to be learned from a chimp like ancestor, but Thorpe's group has turned that argument onto its head.

The researchers argue that bipedalism first appeared in ancient, tree-dwelling apes. The trait of two-legged walking was learned around 6 million years ago in Africa. Africa's dense forests gave way to open space and apes adapted by using branches to swing from branch to branch on ground level. Chimps and gorillas took a less-traveled evolutionary route for primates. They developed bodies suited for climbing trees and walking on all fours. "If we're right, it means you can't rely on bipedalism to tell whether you're looking at a human or another ape ancestor," said anthropologist and study coauthor Robin H. Crompton of the University of Liverpool in England to ScienceNews.org. "It's getting more and more difficult to say what's a human and what's an ape."

Orangutans rarely leave the tree tops, so it took the study more than a year to find sufficient evidence. Researchers found that the orangutans, at Sumatran national park, kept their legs straight while standing of flexible branches. Most humans stand this way when running on a springy surface. The physical alterations of the orangutans from the dense African forest becoming spend out caused the ability to walk upright.

Besides, this study fits in with recent fossil discoveries. The Oreopithecus, a 7-million-to-9-million-year-old apelike creature, lived on what was once a Mediterranean island. It featured a big toe that angled sharply away from other toes on the same foot, which would allow the ape to shuffle short distances to obtain fruit and other food.

The formation the the differences in bodies would explain why two types of bipedalism exists. "It's not surprising that scientists can't agree on whether bipedalism originated in tree-walking apes or ground-striding hominids," says anthropologist Kevin D. Hunt of Indiana University in Bloomington to ScienceNews.org. The long running disagreement seems to center around the when, how, and why bipedaism developed in hominid evolution.

Source:http://www.sciencenews.org/articles/20070804/bob9.asp