Source: NOVA: "In Search of Human Origins"
NARRATOR: A volcanic eruption devastated the landscape near Laetoli, Tanzania, some three and a half million years ago...releasing tons of ash into the atmosphere.
Multiple blasts covered the countryside with sooty sediment. By chance, the eruptions coincided with the rainy season. Rain turned the ash to mud. As the rain let up, animals ventured across the smooth, wet surface, leaving prints. Here, a bird meandered through the muck. And then, an African hare. And eventually, other footprints were left, ones that look as familiar as our own.
Before another rain shower could wash them away, more ash fell, covering the prints and capturing them forever, as the ash hardened into rock. Three and a half million years later, anthropologist Mary Leakey found this path of footprints exposed once more by erosion.
Two individuals clearly walked here. And details of the prints suggest that another followed them... stepping in the prints left by one of those who walked ahead. Footprints can reveal other secrets, too, as forensic scientist Owen Lovejoy knows. (siren) They're often crucial pieces of evidence at crime scenes.
OWEN LOVEJOY, Forensic Scientist: There's no better evidence than that provided by a footprint. That's what makes the Laetoli prints so exciting, because they give us a direct record of how our ancestors walked almost four million years ago.
When we compare the Laetoli print to that of a chimpanzee, the difference is immediately obvious. The chimpanzee, which is a quadruped--but occasionally a biped--still has a free great toe, and that great toe extends out away from the foot and leaves a very distinct mark. On the other hand, when we compare the Laetoli print to that of a crime scene human print, they're virtually indistinguishable.
The great toe is in line with the rest of the toes, and what this has done, in the human and the Laetoli print, is to create an arch, and that's a hallmark of typical modern upright locomotion, because the arch is an energy absorber and that's the kind of fine tuning that you would expect in a biped that had been that way for a very long period of time.
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