New Evidence Supports Bipedalism For Early Hominids

An analysis of the skeletal structure needed to make 3.5 million year old footprints has revealed that our ancient, partially tree-dwelling ancestors walked on two legs. Called bipedalism, this analysis pushes back the date of our hominid ancestors.

[footprint subtext] Images show aerial and lateral images of (top to bottom) (A) a human footprint made walking normally with an extended knee and hip gait; (B) a human footprint made walking with bent-knees and hips to mimic a chimpanzee; and (C) a scan of a cast from the Laetoli fossil trackway. Notice that the toe is much deeper than the heel in the middle print and that the Laetoli scan looks more like the human print. (Credit: Randy Haas, University of Arizona)

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Two years after the stunning discovery of Lucy in 1974 at Hadar in the Awash Valley of Ethiopia’s Afar Depression, a find that revolutionized our understanding of early human ancestry, footprints were discovered in Laetoli, Tanzania by paleoanthropologist Andrew Hill.

The footprints were left in a fresh layer of volcanic ash, which is very easily dateable. They were left by a member of Australopithecus Afarensis, a hominid with gracile morphology (in essence, thinner boned) who, despite not being as avid of brachiators and chimpanzees, spent much of their time in the trees. It is believed that our early ancestors did not abandon their arboreal habitat until around 2 million years ago.

According to

This morphology differs distinctly from our own genus, Homo, who abandoned arboreal life around 2 million years ago and irrevocably committed to human-like bipedalism. Since the Laetoli tracks were discovered, scientists have debated whether they indicate a modern human-like mode of striding bipedalism, or a less-efficient type of crouched bipedalism more characteristic of chimpanzees whose knees and hips are bent when walking on two legs.

David Raichlen, an assistant professor in the University of Arizona School of Anthropology and other researchers from the University at Albany and City University of New York’s Lehman College recreated the footprints, then examined their 3 dimension structure in comparison to those left by modern Homo Sapien Sapiens and chimpanzees, who walk with a bent gait.

Raichlen says, “Based on previous analyses of the skeletons of Australopithecus afarensis, we expected that the Laetoli footprints would resemble those of someone walking with a bent knee, bent hip gait typical of chimpanzees, and not the striding gait normally used by modern humans, but to our surprise, the Laetoli footprints fall completely within the range of normal human footprints.”


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