eLIFE, DOI: http://dx.doi.org/10.7554/eLife.24232.008Recently discovered fossils belonging to Homo naledi appear to be much younger than previously suspected, according to a new study of the remains and surrounding sediments and rocks. The materials were found deep in a South African cave system in 2015, adding H. naledi to the hominin ranks. But researchers were baffled by the species’s mixture of primitive features, such as a relatively small brain case, and modern ones, including feet skeletal morphology similar to that of our own.
Last year, scientists performed phylogenetic analyses that pegged the age of the H. naledi specimens to about 900,000 years. Since then, the scientists who originally unearthed the fossils have suggested that the remains could be hundreds of thousands of years younger.
Now, those more recent estimations have been supported by new chemical aging analyses of the bones and of surrounding inorganic materials. An international team of researchers publishing their work in eLife today (May 9) suggest that the H. naledi fossils were deposited in the Rising Star Cave system between 335,000 and 236,000 years ago.
“The dating of [H.] naledi was extremely challenging,” said coauthor Paul Dirks of Australia’s James Cook University and the University of the Witwatersrand in South Africa, in a statement. “Eventually, six independent dating methods allowed us to constrain the age of this population of Homo naledi to a period known as the late Middle Pleistocene.”
The findings suggest that H. naledi may have mingled with our own species, Homo sapiens, in Middle Pleistocene Africa. They also throw a wrench into theories that modern humans alone left behind a rich record of stone tools in Africa as their large brains developed new technologies and techniques for making a living in a harsh environment. “How do you know that these sites that are called [examples of] the rise of modern human behavior aren’t being made by Homo naledi?” Lee Berger, a University of Witwatersrand paleoanthropologist and coauthor, told National Geographic. “You can imagine how disruptive that could be.”
Two other papers, on which Berger is also a coauthor, published in eLife today add to the evolving picture of H. naledi. One presents new H. naledi fossils dug up near the original find, and supports the claim that the hominin bodies may have been intentionally interred in the cave system. And the other is a think-piece that reimagines hominin evolution in southern Africa in light of the new findings on H. naledi. “My intuition is that Homo naledi points to a diversity of African Homo species that once lived south of the equator,” coauthor John Hawks of the University of Wisconsin-Madison told Science News.
Berger told Science News that he plans on continuing excavations at the Rising Star cave system, where he hopes to find more fossils, tools, and signs of long-extinguished fires used by human ancestors