Laetoli Footprints Those of Completely Bipedal Human

Thirty years ago, a set of footprints was discovered in an ash layer at the African site of Laetoli and dated to 3.6 million years ago. This corresponded to the time range of Australopithecus afarensis but it was not sure whether or not this reflected the gait of afarensis, which was, at the time, thought to be somewhat bent-kneed and not truly bipedal in a modern sense. Now, Science Daily news has a story that reconstruction simulation research has determined that those individuals that made the tracks walked bipedally in a modern fashion. The author writes:

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.

To resolve this, [David] Raichlen and his colleagues devised the first biomechanical experiment explicitly designed to address this question.

The team built a sand trackway in Raichlen's motion capture lab at the UA and filmed human subjects walking across the sand.

"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," Raichlen said.

"But to our surprise, the Laetoli footprints fall completely within the range of normal human footprints," he added.

This is the next step from the bipedal gait found in Ardipithecus, which may have been reflected in the earliest australopithecine, A. anamensis and, perhaps, early A. afarensis. By this point, Bipedalism was the preferred means of getting around.