The find was announced on September 10 by an international team of more than 60 scientists led by Lee R. Berger, an American paleoanthropologist and professor at the University of the Witwatersrand in Johannesburg. The species name,naledi, refers to the Rising Star Cave, located about 30 miles southwest of Pretoria, where the bones were found. “Naledi” means “star” in the local Sesotho language.
In their paper, “Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa” published by the journal eLife, the team details the recovery of 1,550 bones from about 15 individuals, including several virtually complete skeletons. Even though only a small part of the cave has been excavated, this trove already represents one of the richest finds of ancient humans ever unearthed. Because of the large number of skeletons, the fact that they were placed at different times in a deep and almost inaccessible part of the cave, that the bodies were intact when they were deposited and only later began to disintegrate, that no other animals were discovered with the humans, nor were there food or tools which might imply that the hominins lived in the cave, has led the investigators to speculate that the bodies were deliberately placed in the cave, as a form of burial.
Making the find equally remarkable is Homo naledi’s unusual combination of features, some of which are extremely modern, such as the jaws and feet, but other parts just as astonishingly primitive—in some cases, even more apelike than the ancient Australopithecus, the genus that includes the famous Lucy species that lived 3.2 million years ago. As Ian Tattersall from the American Museum of Natural Historyin New York, who was not involved in the discovery, noted, “the species is quite different from anything else we have seen.”
The fossils were discovered by pure chance, when a pair of spelunkers, Steven Tucker and Rick Hunter, discovered a small fissure in a deep part of the Rising Star Cave. Dropping almost 40 feet into the narrow chute, they found a small chamber, the floor littered with bones. The pair took photos of their discovery to Berger, who could see that these bones were not from modern humans. Access to the chamber was so difficult, requiring a very slender frame, that Berger put a team of six women archaeologists together to undertake the excavations. The region of South Africa where the cave is located is famous for the discovery of early human ancestors, so much so that it is known as the “Cradle of Humankind.”
The fossils have yet to be dated, making it difficult to know where they belong in the human family tree. Dr. Berger believes that Homo naledi lived about 2.5 to 2.8 million years ago, though this is just a guess on his part. The rush to publish the find, before dating was done, was not without controversy. Chris Stringer from the Natural History Museum, United Kingdom, responded to the discovery, “Frustratingly, the rich and informative H. naledi material remains undated. Given that this hominin material could conceivably even date within the last 100,000 years, I am puzzled by the apparent lack of attempts to estimate its age.”
While the jaw and teeth of Homo naledi have very modern characteristics, the braincase is extremely small. “Weird as hell,” paleoanthropologist Fred Grine of the State University of New York at Stony Brook said. “Tiny little brains stuck on these bodies that weren’t tiny.” The adult males were around five feet tall and a hundred pounds, larger than Australopithecus. Other parts of the body were equally split between modern and ancient. A fully modern hand yet with curved fingers that might befit a creature climbing trees. The ape-like shoulders and widely flaring blades of the pelvis were as primitive as Australopithecus, but the bottom of the same pelvis resembled those of a modern human. The leg bones start out shaped like an australopithecine but become more modern as they descend towards the ground, leading to feet virtually indistinguishable from our own.
Dr. Berger argues that Homo naledi is the missing link between the more ancient australopithecines and the early homo hominins such as Homo habilis (believed to be the earliest of the human genus) or the later Homo erectus, “The message we’re getting is of an animal right on the cusp of the transition from Australopithecus to Homo. Everything that is touching the world in a critical way is like us. The other parts retain bits of their primitive past.” But some body parts of Homo naledi are even more modern than the same ones on Homo erectus, so until the fossils are dated, the new discovery raises more questions than it answers.
Even more perplexing to the researchers was the means by which the remains got into such a remote chamber. The individuals were not living in the cave, as there were no stone tools or remains of meals to suggest such occupation. A group might have wandered into the cave at one time and somehow got trapped—but the distribution of the bones seemed to indicate that they had been deposited over a long time, perhaps centuries. If carnivores had dragged them into the cave, they would have left tooth marks on the bones, and there weren’t any, nor were almost any other mammals found in the chamber, making it unlikely the cave was a natural trap of some sort that the hominin fell into. And finally, if the bones had been washed into the cave by flowing water, it would have carried stones and other rubble there too. But there is no rubble, only fine sediment that had weathered off the walls of the cave or sifted through tiny cracks.
The team could only conclude that the bodies of Homo naledi were deliberately put there by other Homo naledi. This finding, if confirmed, would shatter the general Western scientific beliefs in the uniqueness of modern humans, a preconception that is largely a relic of the days more than 150 years ago when science was a subset of religious thought. John Hawks, a paleontologist at the University of Wisconsin and one of the team leaders knew the conclusion would be controversial, “We still fight about whether Neanderthal buried their dead. We had to test every alternative.” Other scientists remain unconvinced. “My guess is there’s another explanation,” said Bernard Wood, an expert in early Homo at George Washington University. “We just haven’t found it.”