Homo naledi was very different from archaic humans that lived around the same time. Left: Kabwe skull from Zambia, an archaic human. Right: ''Neo'' skull of Homo naledi. (Image credit: Wits University/John Hawks)
In 2013, researchers in South Africa found the remains of a previously-undiscovered human species. In 2015, they introduced Homo naledi, a human with a tiny brain, ape-like shoulders, but other features that were more human. Where would this species fit in the homo family tree? A big step would be to date the fossils. Using several different methods, a team from the University of Witwatersrand led by paleoanthropologist Lee Berger has determined Homo naledi to be between 236,000 and 335,000 years old, much younger than such a primitive human should be -even younger than Homo erectus.
If these dates hold, it could mean that while our own species was evolving from other, large-brained ancestors, a little-brained shadow lineage was lingering on from a much earlier period, perhaps two million years ago or more. The proposed age range for the fossils also overlaps with the early Middle Stone Age, fueling a provocative, though unproven, possibility: that the stone-tool record in South Africa from that time wasn’t just the handiwork of anatomically modern humans.
“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?” says Berger, who is also a National Geographic explorer-in-residence. “You can imagine how disruptive that could be.”