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.

So rather than quibbling over badly crushed—and often missing—fossil bones, the researchers behind the new study turned much of their focus back to the famous Laetoli footprints, which were discovered more than 30 years ago in what is now Tanzania. Likely left by Australopithecus afarensis, the same species as "Lucy," these prints show an upright gait, but it has remained controversial just how fluid and modern this creature's walk would have been.