The Laetoli footprints were formed and preserved by a chance combination of events—a volcanic eruption, a rainstorm, and another ashfall. When they were found in 1976, these hominid tracks, at least 3.6 million years old, were some of the oldest evidence then known for upright bipedal walking, a major milestone in human evolution. In this NOVA: Evolution video, paleoanthropologist and consultant forensic scientist Owen Lovejoy compares the ancient biped prints with those of modern humans and chimpanzees.
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