Although hominids tracing all the way back to Ardipithecus ramidus (Ardi), an ancestor of ours that lived about 4.4 million years ago, were known to be bipedal, it wasn't clear exactly how those creatures actually moved about. Did early hominids stride about in an upright fashion like modern humans, or used a more shuffling, bent-legged posture like modern apes?
David Raichlen of the University of Arizona and his colleagues studied some 3.6 million year old trackways found in Laetoli, Tanzania to find out. The footprints were made by an Australopithecus afarensis, the same species as ‘Lucy’. Like Ardi, which lived almost a million years earlier, Lucy’s family members spent time in trees as well as on the ground. It would be well over a million years before humans left the trees for good.
Raichlen and his team built sand trackways in Raichlen’s motion capture lab and filmed volunteers walking either upright or in a crouched, chimp-like gait. They then compared three-dimensional models of the new footprints to those found in Laetoli. They were surprised to find that the ancient footprints matched those of humans walking in a modern upright position.