Another wrench has been thrown into our understanding of human origins, thanks to recently discovered remains of an archaic hominin in the Levant. The person or people who left these bones behind over 120,000 years ago may have coexisted with Homo sapiens, according to new research.
Most scientists agree on the geographical starting block for humans, but beyond Africa things get a lot blurrier, as our ancestors and relatives evolved in different ways in different places. Various Homo species competed and interbred, and though our own species is the only one left, our DNA reveals contributions from Neanderthals, Denisovans, and even a third, unknown species.
In 2012, a cement company working at an Israeli lime quarry ran into what appeared to be archaeological remains. They called in a team of paleoanthropologists, who were able salvage the materials from the site, called Nesher Ramla. Over the course of the next six years, two teams of researchers analysed the materials in their labs, eventually identifying an archaic hominin from a skull fragment, a mandible, and teeth. One team said that the skull fragment was indicative of archaic members of the genus Homo from the Middle Pleistocene, but the jaw and teeth were similar to that of Neanderthals. The results are published in two separate papers today in Science.
“For many years, the dominant interpretation among our colleagues was that Neanderthals came from Europe, only from Europe,” said Rachel Sarig, a dental anthropologist at Tel Aviv University and a co-author of one of the new papers. “And now we bring new data, and based on the new data, we suggest a new interpretation for this complex issue of human evolution.”
Sarig’s paper describes the physical characteristics of the remains from Nesher Ramla, and the other paper describes the stone tools found at the site. The bones were compared to other members of the genus Homo using 3D morphometrics — basically, the researchers created a dataset of points in three dimensions and looked at how similar or dissimilar the skull fragment, jawbone, and teeth were from those of other humans. They also dated the specimen to between 140,000 and 120,000 years old, which would mean it lived at the same time as Homo sapiens in the area.
“The Nesher Ramla fossils certainly complicate a straightforward evolutionary story, which traditionally hinged on exclusive occupation of the Levant by either Neanderthals or Homo sapiens,” said Michael Petraglia, an archaeologist at the Max Planck Institute for the Science of Human History who was unaffiliated with the recent papers. “Instead, there may be multiple species around at the same time, sometimes interbreeding, learning from one another and sharing in their cultural behaviours.”
The stone tool age isn’t certain, though; one of the tools was dated using thermoluminescence to 190,000 years ago, but it’s possible that two separate occupations of the site are being mixed up, according to Huw Groucutt, a paleoanthropologist also at the Max Planck Institute for the Science of Human History who wasn’t involved in the new studies. “The dating is a bit of a mess,” Groucutt said. “It is always possible to make things look neat by citing averages — but the range of results really matters.”
“Maybe the interpretation of the Nesher Ramla fossils is correct, but I think we should be cautious before we re-write the textbooks,” Groucutt added. “And suggestions of cultural interaction between hominin species seem a bit of a jump to me. I think before we start thinking about that kind of idea, we need to be more secure on the ages and dates of fossils and archaeological materials.”
The researchers intentionally did not assign the Nesher Ramla remains to a species, instead referring to them as an archaic Homo. Where the specimens sit on the family tree is “a million-dollar question,” according to Israel Hershkovitz, one of the study’s lead authors and a paleoanthropologist at Tel Aviv University. “One of the problems in human paleontology is the plethora of species … I believe that the story is much simpler: almost all Homo paleodeme (a group of people that can be recognised by their morphological features), belong to a single species.”
Hershkovitz’s suggestion that most of the hominins identified under the Homo genus should actually be just one species is bound to be controversial — though, as he points out, Neanderthals and modern humans could produce fertile offspring, a sign of how similar we were. But it’s important to remember the entire concept of categorising organisms into species is a human construct that’s imperfect. The team’s decision to avoid assigning these bones and teeth to any particular identity is a reflection of that ambiguity — that many specimens fit into grey areas between species.
Hershkovitz’s team also argues that the Nesher Ramla Homo represents one of the last surviving members of what may have been a source population for other archaic hominins in other caves in the area. The dating and taxonomic identities of those fossils — meaning exactly which Homo group they belong to — is still debated.
“The mismatched morphological and archaeological affinities, and the location of the site at the crossroads of Africa and Eurasia make this a major discovery,” wrote Marta Mirazón Lahr, a human evolutionary biologist at the University of Cambridge, in a Perspectives article accompanying the publication of the two papers. “The new remains from Nesher Ramla add to the emerging complexity in the hominin evolutionary landscape of the last half million years.”
Unfortunately, finding new fossils doesn’t always answer our big questions — instead, we just end up with more mysteries to solve. In this case, the new evidence is forcing us to rethink pre-existing notions about human evolution, dispersal, and behaviour in the millennia before Homo sapiens took over.