A jaw-dropping new hominin fossil find made headlines worldwide in early September: Lee Berger, paleoanthropologist, uncovered a new species of Homo in South Africa. But what does this astonishingly rich discovery tell us about the origins of humanity, and what mysteries remain to be solved?
Homo naledi had a small brain, apelike shoulders for swinging, modern hands but with curved fingers, fingers with pad-like tips (interpreted as being useful for tool-making, although I can imagine other uses), skinny longbones (indicating a slender stature), a primitive Lucy-like hip, and feet that look indistinguishable from modern human feet. The teeth are a hodgepodge of characters, with some human-like anatomical features (such as the molar surfaces), and some primitive features (premolar roots).
I attended a recent seminar talk given by John Hawks, who presented the seemingly contradictory anatomical characters summarized above, and who estimated that H. naledi stood about 135-145 cm tall and weighed 38-55 kilograms-- that is, about 4' 7" and 95 pounds. These skeletal descriptions and estimates are derived from the vast collection of fossils found-- over 1500 specimens of at least 15 individuals have been found, and there are likely more to come.
So, what questions does Homo naledi answer? And what new questions does it raise?
Bipedalism: Already, H. naledi indicates that our previous inferences about foot shape and hip shape may be incorrect-- this species had essentially modern feet, but primitive hips. What does that imply for the evolution of bipedalism?
Location: The location of these fossils was a huge surprise to many members of the paleoanthropology community (although Lee Berger has been expecting such a find in South Africa for years); many people assumed that more specimens of Homo would come from East Africa, rather than South Africa.
Age: A central question of massive importance is this: how old are these fossils?! Since they were found in soft, loose sediment in a cave, they are very difficult to date-- all we can say about this for now is stay tuned!
Cause of death? The question that has likely captured the most popular attention is what on earth happened? The cave where these fossils were found is extremely inaccessible (the research team famously recruited slender cavers with anthropological experience to navigate the tricky passageways). Very few animal bones were found alongside the humans, so little information can be gleaned from other fauna. Further, the fossils show no evidence of predation, and are roughly equally distributed across ages. Scientists who found these fossils have suggested that this cave represents a ritual dump of bodies-- so, individuals dragged bodies into the cave and dumped them, an early burial system. It is possible that the cave was more easily accessible in the past, which seems almost required for that theory to hold water.
But what else could be true? Did all of these individuals separately crawl into the cave and fall (or die, unable to get out)? They weren't swept there by water, since the cave is devoid of other fauna (or rubble and plant material). It seems likely that these bodies were placed there deliberately.
For now, the most important priority is getting an age on these fossils. And perhaps the most exciting conclusion from these finds is eloquently put by Jamie Shreeve, the writer of the linked National Geographic article:
"If we learned about a completely new form of hominin only because a couple of cavers were skinny enough to fit through a crack in a well-explored South African cave, we really don’t have a clue what else might be out there."
A trove of bones hidden deep within a South African cave represents a new species of human ancestor, scientists announced Thursday in the journal eLife. Homo naledi, as they call it, appears very primitive in some respects—it had a tiny brain, for instance, and apelike shoulders for climbing. But in other ways it looks remarkably like modern humans. When did it live? Where does it fit in the human family tree? And how did its bones get into the deepest hidden chamber of the cave—could such a primitive creature have been disposing of its dead intentionally? This is the story of one of the greatest fossil discoveries of the past half century, and of what it might mean for our understanding of human evolution.