The Rising Star cave system continues to reveal more about life 250 000 years ago.
In September 2015, when paleoanthropologist Professor Lee Berger and his team announced the richest hominin fossil site ever discovered, along with a new species called Homo naledi, they admitted they were unsure of the age of the new species. The team is now confident that the remains in the Dinaledi Chamber of the cave system were alive between 335,000 and 236,000 years ago.
“The range of methods and the rigour we applied to determine the age of the Dinaledi Chamber and associated fossils gives us great confidence that the age attributed to the fossils is correct,” Professor Paul Dirks told journalists at a press conference at the University of the Witwatersrand.
It means that the small-brained primitive hominins were alive at the same time as Homo sapiens. This is the first evidence of a primitive related species surviving alongside the first humans in Africa. Berger says the impact of the age of the Homo naledi fossils brings into question our understanding of archaeological sites and prehistoric tools.
As he says in the paper Homo naledi and Pleistocene hominin evolution in subequatorial Africa: “We can no longer assume that we know which species made which tools, or even assume that it was modern humans that were the innovators of some of these critical technological and behavioural breakthroughs in the archaeological record of Africa.”
Berger goes on to say that this could also mean that there were other primitive species that shared the world with modern humans. Co-author John Hawks, of the University of Wisconsin-Madison and Wits University, says the age of the naledi find shows just how much we still need to learn. “I think some scientists assumed they knew how human evolution happened, but these new fossil discoveries, plus what we know from genetics, tell us that the southern half of Africa was home to a diversity that we’ve never seen anywhere else.”
The discovery of the Lesedi Chamber
The original find in the Dinaledi Chamber, some 1,550 bones and teeth, suggested a species related to the Homo genus. Despite their small brain size, their physical traits suggested sophisticated behaviour, which made discovering the age of the fossils essential.
The primitive features of the fossils suggested links to Lucy, the shape of their pelvis was associated with Australopithecus and their leg and foot resembled those of Homo sapiens. This evolutionary soup suggested a new species to Berger and his team.
Ongoing excavations in the chamber led to the discovery of a second chamber, named Lesedi by the team. In the second chamber the team discovered a partial skeleton with a complete skull. It is as difficult getting to the Lesedi Chamber as it was to get into Dinaledi. This, in Hawks opinion, re-enforces the team’s original hypothesis. “Homo naledi was using dark, remote places to cache its dead. What are the odds of a second, almost identical occurrence happening by chance?”
Neo, the face of Homo naledi
The skull discovered in Lesedi, nicknamed Neo, a Sesotho word meaning “a gift”, finally gives researchers a clear picture of what Homo naledi looked like. And it is nearly identical to those found in the Dinaledi Chamber, leading Hawks to conclude that they belong to the same species.
Berger believes that his team has only just scratched the surface at the Rising Star dig. The age of the bones has opened a whole raft of questions that need answering, work he believes could take decades. The most important question for him remains: what was life like for Homo naledi and how did they interact with their more evolved cousins?
In the meantime, the team is working slowly and carefully so as not to damage the site. “We are going to treat ongoing extraction of material from both of these chambers with extreme care and thoughtfulness and with the full knowledge that we need to conserve material for future generations of scientists, and future technological innovations,” Berger says.