Footprints Offer Evidence of Two Ancient Human Species Coexisting
We know other human species once roamed Earth, but this find is the first demonstration of two species directly coexisting - and Homo sapiens aren't one of them.
Hiya!
We may be the last human species standing, but we’re far from the first to exist. Archaeologists have unearthed over a dozen human species who walked the Earth for millions of years before we came along. So, while we modern humans are alone now, our ancient Homo sapien relatives weren’t.
Analysis of skeletal remains tells us that our ancestors coexisted and even mated with other human species. Now, for the first time, scientists have discovered visible proof of co-hominin existence not from bones but from 1.52 million-year-old footprints. For reference, that’s roughly 1.2 million years before our Homo sapien ancestors entered the evolutionary scene.
Initial Discovery
The story behind a recent study published in the journal Science on November 28, 2024, begins during an excavation in 2021 led by paleoanthropologist Louise Leakey of the Turkana Basin Institute and Stony Brook University in New York.
At the time, Leakey and other experts from the Koobi Fora Research Project and the Turkana Basin Institute were unearthing hominin skeletal fossils from sediments on the eastern shore of Lake Turkana in Kenya at a site called Koobi Fore when they noticed several preserved tracks.
Many of the footprints resembled ones left by large birds, but world-renowned paleoanthropologist and conservationist Richard Loki, who passed away in January of 2022, is credited with being the first to recognize that at least one of the tracks was a hominin footprint. Upon this recognition, the team did their best to protect the print until they could return for a closer look.
Leakey then coordinated a team led by Kevin Hatala, a paleobiologist at Chatham University, and returned in July of 2022 to investigate the footprint.
A Closer Look
The team excavated 249 square feet (23 square meters) around the hominin footprint Loki identified and discovered 12 complete hominin tracks in a straight line, likely from a single individual. They also found three isolated hominin footprints nearby, which seem to have been left behind by three separate individuals.
Beyond the human-like prints, the team found dozens of wildlife tracks, including three horse-like tracks, 30 cow-like ones, and 61 bird tracks — including a few from an extinct giant stork species called Leptoptilos Falconeri. Fun Fact: The largest bird track they found was over 10 inches (over 25 cm) across.
What’s especially exciting about the prints, human or otherwise, is the lack of cracking or overprinting in the mud, suggesting the tracks were made around the same time. Hatala told Michael Marshall of New Scientist:
“These sites probably capture a window of time anywhere from minutes to a few days or so.”
Dating of the sediment shows the prints were made around 1.52 million years ago, and the researchers think they were covered up with sand and sediments shortly after because the footprints don’t show signs of cracking, which suggests that they were likely not exposed to the elements for long and likely made around the same time. This means that the life forms that created the prints probably crossed paths.
Further Investigation
The 15 non-wildlife footprints were clearly hominin because they were similar to ours, but the scientists couldn’t determine if they were left by one or multiple human species at first.
Hatala, a co-author of the study, told Katrina Miller of the New York Times that since fossilized remains of our human ancestors are rare, they couldn’t “do the Cinderella thing of fitting the foot skeleton into the footprint” to determine which ancient human relative left the prints behind.
Thankfully, this is 2024, and scientists don’t need to match skeletons to footprint fossils Cinderella style.
Instead, the team created detailed 3D images of the footprints to compare to other specimens and discovered differences in toe angles and arch depth in the foot anatomy. These differences would also affect the animal’s gait. The results suggested that at least two hominin species visited the lake around the same time.
Homo erectus
Of all the hominin footprints, the three isolated ones most resembled modern humans as they indicate that the heel stuck to the ground first, followed by the foot rolling forward and pushing off the ground with the toes. Hatala and his team believe Homo erectus left them, who are known to have lived in the area.
In my opinion, H. erectus was the supreme human species, and we can learn a lot from them. Compared to other early hominins, they had larger brains, and while their heads resembled apes more than humans, their bodies were more like ours.
This human species was likely the first of our clade to travel beyond Africa, spreading into today’s Middle East and southern Asia. They also walked on two legs, had a diverse diet, and may have cooked with fire.
What I find most impressive, though, is that they existed on Earth for nearly two million years and hold the title of the longest-living hominin species — whereas our H. sapien species has only been around for about 300,000 to 400,000 years.
The footprints Hatala and his team excavated date to about halfway through H. erectus's reign. After the prints were made, the species remained alive for at least another one million years.
Paranthropus boisei
Meanwhile, analysis shows a more flat-footed hominin species left the continuous trackway of a dozen footprints. The researchers believe it could have been our lesser-known cousin, the Paranthropus boisei, another human ancestor known to have lived in the area.
Compared to H. erectus, P. bosei had a more ape-like appearance and a smaller brain. They also had the thickest dental enamel of any known early human, along with large molars and chewing muscles, which likely helped them munch on touch plants and hard nuts.
Archeologists have unearthed mostly leg and arm bones from archeological sites, but few skulls are attributed to the Paranthropus family. Because scientists have few skeletal remains, they know little about P. bosei’s bodies. This means experts were unsure whether they walked on two legs or four — but the newly discovered trackway changes that. Wiseman says the continuous footprints Hatala and his team identified are “unequivocal evidence of walking on two legs.”
Coexistence
Beyond computer modeling, another contributing factor to the researchers' assigning H. erectus and P. bosei as the owners of the footprints is that they are the only early hominin species known to have lived in the area.
In fact, fossil evidence suggests the two hominin species may have shared the lakeshore area for as long as 100,000 years. If that’s true, Hatala told Miller it’s likely H. erectus and P. bosei had some kind of harmonious coexistence — or at least weren’t in competition with each other.
After analyzing the tracks Hatala and his team found, they examined other footprints discovered in the same area from the same period and discovered they matched one of the two examples they excavated. Hatala explains,
“We see a similar pattern at multiple other sites, and they might span more than 100,000 years. It seems like these two species were coexisting on this same immediate landscape with one another for a very prolonged period of time.”
Seeing as food is a significant factor in competition between species, scientists believe differences in diet may explain the long period of peaceful cohabitation. Using their powerful jaws, P. boisei mostly ate tough grass-like plants known as sedges. Meanwhile, E. erectus were omnivores that ate meat and other plants to fuel their large brains.
Bernard Wood, a paleoanthropologist at George Washington University who was not involved with the study, pointed out to Bruce Bower of Science News that if P. boisei and E. erectus weren’t in direct competition for resources, it’s likely the two hominin species, along with untold wildlife, treated the Kenyan lake as a “1.5-million-year-old version of a 7-Eleven store.”
I can’t help but imagine how cool it would be to hang out at a lake only to look up and see another species that’s similar to, but different from, us. Then again, I suppose it wasn’t an unusual sight for them to see each other if they coexisted for so long.
Perspective Shift
It’s one thing to use DNA analysis and fossil records to piece together evidence showing multiple human species coexisted in the same areas at the same time, but it’s somehow more magical to see the evidence through footprints. While an analysis provides data, footprints reveal actions.
I’m often curious about who or what walked where I walk or lived where I live long before modern houses existed. The footprints the scientists identified tell us who walked along that lake while painting a snapshot of life over a million years ago.
I sometimes wonder what today would be like if H. erectus, the Neanderthals, the Denisovans, or any of our other human relatives had survived with us. Then again, considering our Sapien species' struggles with getting along, maybe I don’t want to know. Regardless, I can’t wait to find out what scientists learn about our hominin family next.
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Fascinating