Human ancestors walked comfortably upright 3.6 million years ago, new footprint study says

A comparison of ancient and contemporary footprints reveals that our ancestors were strolling much like we do some 3.6 million years ago, a time when they were still quite comfortable spending time in trees, according to a study which will be published in the March 22 issue of the journal PLoS ONE.

Anatomical fossils have given scant confirmation about when our ancestors developed a fully modern gait. Although some researchers have argued that the 4.4 million-year-old ancient human Ardipithecus ramidus ("Ardi") described in October 2009 was adept at walking on her hind legs, many disagree.

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