A new study in Science describes an approximately 1.5 million-year-old fossil footprint site in northern Kenya that records, for the first time, two different kinds of ancient human footprints that reflect different patterns of anatomy and locomotion. It is the first direct evidence showing that Homo erectus and Paranthropus boisei, two ancient human species, occupied the same lake margin environment and likely interacted.
“Despite these two hominins diverging considerably in their anatomy, behavior, and land use, they are both clearly drawn to these important lakeshore environments,” said study co-author Neil Roach, of Harvard’s Department of Human Evolutionary Biology. “It raises new questions like, ‘Did this overlap increase competition between them for the same resources? Were they there for different purposes?’”
For much of humans’ evolutionary history, scientists have thought that multiple human relatives may have coexisted within the same geographical regions and time periods. This has driven numerous hypotheses about the importance of niche partitioning and competition between species in human evolution. However, the paleontological record has been unable to definitively establish whether these ancient human relatives actually lived together on the same landscapes simultaneously, until now.
The research team expanded its analyses to other fossil footprint sites known from the surrounding area and found more evidence that these two species not only overlapped in time, but lived in close proximity over 200,000 years. This combination of data suggests low to neutral competition between these two species, which may have enabled their long-term coexistence during the early Pleistocene.
Later, environmental shifts could have impacted resource availability, increasing competition and potentially driving the behavioral adaptations that have come to define our genus.
During this time and place in human evolution — about 1.5 million years ago in the Turkana Basin of Kenya — it had long been hypothesized that these fossil human species coexisted. Homo erectus, a possible direct ancestor of ours, persisted for more than a million years after this. The other, Paranthropus boisei, went extinct within the next few hundred thousand years.
“Perhaps changes to climate influenced resource availability, and that led to the extinction of Paranthropus and the persistence of Homo,” said lead author Kevin Hatala of Chatham University. “This is a hypothesis that will require further testing, and we’re hopeful that by combining fossil footprints with other kinds of paleontological and archeological data, we might be able to build a better understanding of how factors like competition and niche partitioning played a role in our evolutionary history.”
Said co-author Kay Behrensmeyer, of the Smithsonian’s National Museum of Natural History: “Documenting the strata revealed that there are many more trackway surfaces nearby. These might hold clues that could be used to address questions about how different species interacted, and what they were doing wading in shallow water.”
The research was supported by the National Geographic Society, National Science Foundation, Turkana Basin Institute, and UK Research and Innovation.
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