Our ancestry: Homo Naledi, Homo Superman?

naledi
Facial reconstruction of Homo Naledi. Photograph by Mark Thiessen, National Geographic.

This past week, articles began to pop up all over the internet regarding the find of a new species of human ancestor, imaginatively named Homo Naledi after the South African cave where the remains were found. Those of you who know me will know that finds like these make me as giddy as a kid in a candy store. So, be warned. Proceed at your own caution. There are actual dragons ahead.

Why is this find so interesting? What sort of impact could it have on our understanding of hominin (the group consisting of modern humans, extinct human species, and our immediate ancestors) evolution?

The Homo Naledi find has proper boat-rocking potential. In true Indiana Jones fashion, the site was discovered by cavers, who knew there might be bones in caves and were looking for previously untrodden passages. After working their way through a passage called the Superman’s Crawl (because most people can only fit through the narrow gap by extending one arm above their heads and the other pressed against their bodies, like Superman in flight), and crossing the rocky ridge known as the Dragon’s Back, they found a fissure in the floor leading into a vertical chute. In what I’m sure you realise by now is a highly inaccessible place that won’t win any wheelchair-friendly awards, they uncovered a chamber from which the bones of at least fifteen (!) excellently preserved specimens would be excavated. This is a huge amount. Usually, finds are restricted to the odd skeletal part here and there. Before going into more detail about this new species, a bit more context about our broader human lineage might be useful.

Now, there’s an interesting gap in the fossil record of our genus, Homo, that this find might play into. As one scientist put it, current Homo finds that are dated between 3 and 2 million years ago can all be contained in one shoe box, while leaving space for the shoes. On the far end of this gap, we find what is commonly considered to be a very early direct ancestor of ours, the Australopithecines. The well-known specimen “Lucy”, dated to 3.2 million years ago, belongs to the species Australopithecus Afarensis. They walked upright on two legs, but were a lot smaller than us and had considerably smaller brains (than most of us). They were more apish than human, so to say. Our own genus, Homo, possibly emerged around 2.8 million years ago, but becomes recognisably represented in the fossil record around 2 million years ago with Homo Habilis and Homo Erectus. These were larger-brained handymen who used stone tools and, as we know for sure with regard to Homo Erectus, harnessed fire and became Masterchefs.

So how does Homo Naledi fit into this story? The bones they uncovered were mildly confusing, to say the least, and have a bit of a Dr. Jekyll & Mr. Hyde vibe to them. On the one hand, the fossils sported characteristics that had surprisingly modern human features, but at the same time some parts were quite primitively apish. The top half – shoulders, torso, and flared hips – reminds us more of our very early Australopithecine ancestors, whereas the bottom half with its long legs and humanlike feet appears very much human. The skull and teeth show an interesting mix of the two; the braincase was less than half the size of ours, but it was quite modern, and more similar to Homo Erectus than Homo Habilis is.

Thus – you’ve guessed it – Homo Naledi might be placed somewhere in between Australopithecus and Homo Erectus, at perhaps around 2 to 2.5 million years ago, in which case it would fill in some of the blanks of the shoe-box era. This is by far the most likely scenario. The problem is that so far they haven’t managed to date the find, because apparently bottom-of-a-cave mixed sediment presents a bit of a problem. So we can’t shout it from any rooftops just yet. Also, if it somehow turns out to be much older, it might contest the idea that Australopithecus is our direct ancestor. In that case it might also be connected to the recent discovery that has pushed back the date of the earliest known stone tools to an astonishing 3.3 million years old (so, before any thus far known species of Homo were around). And if it happens to be a lot younger, it places a small-brained Homo alongside a lot of advanced Homo bigheads.

However interesting this is, I’m even more intrigued by another feature of the find. At least fifteen skeletons, found in a Mission Impossible worthy remote part of a cave, preserved without any tools or animal bones to suggest that they might have lived there. How on earth did they get there? There were no tooth marks on the bones to suggest predatory gnawing and dragging into lairs, and no rubble or stones to indicate the bones had been washed there by a river or a flood. Also, the way the bones were distributed points to intervals between the deposition of the specimens. According to Lee Berger, the paleoanthropologist who led the excavation, the only likely explanation seems to be, to quote Boromir, that ‘This is no mine. It’s a tomb!’ Deliberate burial or disposal of bodies. Far, far earlier than our current earliest evidence of burials. Only Homo Sapiens and perhaps Neanderthals are thus far associated with this sort of ritualisation of death. Moreover, because the chamber is so hard to reach and very, very dark indeed, torches or lit fires must have been necessary. This is very advanced behaviour for a creature with such a small brain.

Of course, there could have been a different entrance to the chamber all those long years ago. In that case, perhaps fire wasn’t a definitive requirement at all. And even though the sediments scream out against the bones having washed in, I think it might perhaps be too big of a leap to pin this deposition of bodies in the category of ‘ritualised’ burials. Perhaps the Naledi simply found a convenient chasm nearby their living place to chuck their dead into, so they weren’t staring at them all the time while they rotted.

But, whichever way you spin it, this new species sure throws us a curveball and makes us rethink some of our previous assumptions. Oh yeah, and the find’s location in South Africa, rather than East Africa where most other human fossils are found, might end up changing our perspective about our origin story, too. Not a bad score for one find. I for one eagerly await the day they finally manage to date these remains.

(Further reading: http://news.nationalgeographic.com/2015/09/150910-human-evolution-change/)

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