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Humans' Tree-Dwelling Ancestors May Have Also Walked Upright

TUESDAY March 23, 2010 -- Fossil footprints made 3.6 million years ago are the earliest direct evidence that our tree-dwelling ancestors walked on two legs, U.S. researchers say.

The fossil footprints preserved in volcanic ash were discovered in Tanzania more than 30 years ago. Since then, experts have debated whether the tracks indicate a modern human-like bipedal stride.

In this new study, researchers built a sand trackway in a laboratory and filmed volunteers as they walked across the sand in a normal manner and in a crouched, chimpanzee-like gait. Three-dimensional models of the footprints were compared with the fossil footprints, which were found to be similar to modern human footprints.

"This more human-like form of walking is incredibly energetically efficient, suggesting that reduced energy costs were very important in the evolution of bipedalism prior to the origins of [modern humans]," study author David Raichlen, an assistant professor in the University of Arizona School of Anthropology, said in a university news release.

"What is fascinating about this study is that it suggests that, at a time when our ancestors had an anatomy well-suited to spending a significant amount of time in the trees, they had already developed a highly efficient, modern human-like mode of bipedalism," study co-author Adam Gordon, of the University of Albany, said in the release.

The study was published online March 22 in the journal PLoS One.

More information

Minnesota State University has more about human evolution.

Posted: March 2010


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