Archaeologists Found Ancient Footprints of Two Human Species Whose Paths Mysteriously Crossed
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In 2021, scientists discovered sets of ancient human footprints—now known as the Koobi Fora footprints—in northwest Kenya.
A new study determined that these footprints actually contain evidence of two distinct human species: Homo erectus and Paranthropus boilei, an australopithecine.
This suggests these two species likely interacted with each other, and provides a rare snapshot into a brief moment in human history.
Homo erectus—the direct ancestor of modern humans and the longest-lived hominin—walked the Earth for some two million years. But it didn’t walk alone. The most stunning example of this fact is the Koobi Fora footprints found in northwest Kenya. First discovered in 2021 and dating back 1.5 million years to the Calabrian subdivision of the Pleistocene Epoch, these tracks stretch 26 feet long and contain one set of 12 footprints made by one individual and three footprints made by others (as well as the noticeably different tracks of a long-extinct giant marabou stork, Leptoptilos falconeri).
Of course, footprints of ancient human species have been found in eastern Africa before. In 1974, for example, footprints of Australopithecus afarensis—who traipsed through wet volcanic ash one day millions of years ago—were found in Tanzania, providing one of the earliest pieces of evidence for human bipedalism. Despite this watershed moment in anthropology, the Koobi Fora footprints display something altogether different: they actually contain evidence of two distinct species of humans.
In a study published last week in the journal Science, researchers announce that they discovered that the Koobi Fora footprints—which were likely located along an ancient lake shore 1.5 million years ago—actually contain a set of footfalls belonging to both H. erectus (who had a similar gait to modern humans) and Paranthropus boilei (a more broad-faced australopithecine with specialized adaptations for heavy chewing). Using 3D X-ray-based imaging, the scientists analyzed the footprints and discerned that the continuous track—the one containing a dozen footfalls—belongs to P. boilei, while the others belonged to H. erectus.
Scientists were primarily able to discern these differences due to the position of P. boilei’s flatter foot and big toe, which had a greater range of motion (up to 19 degrees) than what’s seen in modern humans (around 10 degrees). That may not seem like a big difference, but this subtle adaptation is what allows humans to walk and run without accruing physical foot abnormalities over time.
“These fossilized footprints are as close as we are going to get to having a time machine to take us back to an eastern African lakeshore 1.5 million years ago,” Bernard Wood, a co-author of the study and a paleoanthropologist from George Washington University, told Nature. “We can only assume they were aware of each other’s presence. Exactly how they interacted, or whether they learned from each other or what, that’s still a mystery.”
This paints a remarkable scene of two ancient human species possibly interacting and co-existing with each other in east Africa. Of course, evidence of hominin fraternization exists in our DNA, as many people of European and Asian descent carry at least one to two percent of Neanderthal DNA in their genome. But rarely can fossils capture such a unique moment in time.
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