Rising Star (Af. Du Sud) : Homo naledi's surprisingly young age opens up more questions on where we come from

PART. 2 

No easy access

"To access the Lesedi Chamber is only slightly easier than the Dinaledi Chamber," says Elliott, who was lead excavator of the fossils from the new locality. "After passing through a squeeze of about 25cm, you have to descend along vertical shafts before reaching the chamber. While slightly easier to get to, the Lesedi Chamber is, if anything, more difficult to work in due to the tight spaces involved."

Hawks points out that while the Lesedi Chamber is "easier" to get into than the Dinaledi Chamber, the term is relative. "I have never been inside either of the chambers, and never will be. In fact, I watched Lee Berger being stuck for almost an hour, trying to get out of the narrow underground squeeze of the Lesedi Chamber." Berger eventually had to be extracted using ropes tied to his wrists.

The presence of a second chamber, distant from the first, containing multiple individuals of Homo naledi and almost as difficult to reach as the Dinaledi Chamber, gives an idea of the extraordinary effort it took for Homo naledi to reach these hard-to-get-to places, says Hilbert-Wolf.

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. Credit: John Hawks/University of Wisconsin-Madison
"This likely adds weight to the hypothesis that Homo naledi was using dark, remote places to cache its dead," says Hawks. "What are the odds of a second, almost identical occurrence happening by chance?"

So far, the scientists have uncovered more than 130 hominin specimens from the Lesedi Chamber. The bones belong to at least three individuals, but Elliot believes that there are more fossils yet to be discovered. Among the individuals are the skeletal remains of two adults and at least one child. The child is represented by bones of the head and body and would likely have been under five years of age. Of the two adults, one is represented by only a jaw and leg elements, but the other is represented by a partial skeleton, including a mostly complete skull.

Meeting naledi

The team describes the skull of the skeleton as "spectacularly complete". "We finally get a look at the face of Homo naledi," says Peter Schmid of Wits and the University of Zurich, who spent hundreds of hours painstakingly reconstructing the fragile bones to complete the reconstruction.

The skeleton was nicknamed "Neo" by the team, chosen for the Sesotho word meaning "a gift". "The skeleton of Neo is one the most complete ever discovered, and technically even more complete than the famous Lucy fossil, given the preservation of the skull and mandible," says Berger.

The specimens from the Lesedi Chamber are nearly identical in every way to those from the Dinaledi Chamber, a remarkable finding in and of itself. "There is no doubt that they belong to the same species," says Hawks. The Lesedi Chamber fossils have not been dated yet, as dating would require destruction of some of the hominin material. "Once described, we will look at the way forward for establishing the age of these particular fossils," says Dirks. Elliot adds, however, that as the preservation and condition of the finds are practically identical to that of the naledi specimens from the Dinaledi Chamber the team hypothesizes that their age will fall roughly within the same time period.

Berger believes that with thousands of fossils likely remaining in both the Lesedi and Dinaledi Chambers, there are decades of research potential. "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," he says.

52 scientists from 35 departments and Institutions were involved in the research.

Wits Vice-Chancellor and Principal, Professor Adam Habib said: "The search for human origins on the continent of Africa began at Wits and it is wonderful to see this legacy continue with such important discoveries"

"The National Geographic Society has a long history of investing in bold people and transformative ideas," said Gary E. Knell, president and CEO of the National Geographic Society, a funder of the expeditions that recovered the fossils and established their age. "The continued discoveries from Lee Berger and his colleagues showcase why it is critical to support the study of our human origins and other pressing scientific questions."

More information: Paul HGM Dirks et al. The age of and associated sediments in the Rising Star Cave, South Africa, eLife (2017). DOI: 10.7554/eLife.24231

John Hawks et al. New fossil remains offrom the Lesedi Chamber, South Africa, eLife (2017). DOI: 10.7554/eLife.24232

Lee R Berger et al. , a new species of the genusfrom the Dinaledi Chamber, South Africa, eLife (2015). DOI: 10.7554/eLife.09560