The recent discovery of the new member of the human family - Homo naledi - is very important for our understanding of human evolution. It helps confirm a lot of ideas we had about our ancestors (and as an added bonus, confuse creationists). However, there is one aspect of this find which contradicts existing ideas. This ancient, archaic hominin may have done a very modern thing: Did Homo naledi bury its dead?
The earliest clear evidence of our ancestors burying their dead is around 100,000 years old; from the Middle East. There is some (albeit contentious) evidence of burial occurring even earlier, in Spain ~400,000 years ago. Yet it is suggested that Homo naledi may have been burying their dead almost 2 million years ago! As if that isn't shocking enough; there's also the fact it had a brain the size of gorilla. Could an animal without our intelligence engage in such a human-like behaviour?
The evidence for this is pretty strong. The cave in which Homo naledi was found contains at least 15 individuals. These were found at varying depths in the sediment, suggesting that they accumulated over time. Such a long period and large accumulation suggests that something was going on here.
Now, burial isn't the only "something" which could cause this sort of accumulation. A nearby cave in South Africa contains a lot of hominin fossils as well. This appears to be the result of the fact the cave used to have a hole in the roof. Unsuspecting Australopithecus wandering through the area fell in these imaginatively titled "death traps" and - you guessed it - died.
However, the thing about holes in the ground is that they don't discriminate. As such, Malapa cave contains several other animals, as well as the human fossils. Yet Rising Star Cave - where Homo naledi was found - only contains fossils of Homo naledi (and a few other small animals that could get in their on their own steam). Plus, there's no sign that there ever was a hole in the roof of the cave.
Another likely alternative is that predators carried these animals into the cave to store and/or eat. We know that our early ancestors were easy prey, having found human fossils with bite marks. Yet these bitemarks are missing from the Homo naledi fossils. In fact, they don't show much pre-death damage at all (or even signs of being eaten after death). All of the damage seems to have been done by bugs eating the decaying corpses. Or the changing levels of moisture in the cave breaking bones.
However, this doesn't necessarily prove that no predators were involved. Perhaps the animal that stored the bones here forgot about them. Alternatively, since most of the fossils are partial skeletons the evidence of biting could simply be on the pieces we don't have. That said, the researchers examining the cave claim this is an unlikely explanation since it's so hard to reach the chamber the fossils were found in. Hell, it was really hard for the palaeoanthropologists to reach; requiring all sorts of gizmos and tiny people. As such, big cats probably wouldn't have been routinely making that journey.
Other explanations they ruled out include the possibility water moved the bodies in there; since the deposits are relatively undisturbed. Or that these are just the result of individuals living in the chamber (since it's so hard to get to).
So the only explanation left seemed to be that it was Homo naledi itself placing the bodies in the chamber. The bodies could be dropped down a slope into the chamber, avoiding the navigational difficulties that would've stopped predators reaching that inner room. If true, this behaviour would be very significant. This seems to be a case of a small-brained human relative engaging in the sort of symbolic behaviour we thought you needed a large brain for. In fact, burial of the dead is often thought to be one of those key developments that heralded the arrival of modern(ish) levels of intelligence.
However, before we get too far into a discussion of this finds significance it should be noted that there are a few issues with this conclusion. For starters, the Homo naledi fossils haven't been dated yet. Sure, this would be very significant if it's a case of 2 million year old humans burying their dead. But if it turns out it was happening last Tuesday (geologically speaking) then a lot of that significance vanishes. There's also the fact that only a small part of fossils site 101 has been excavated thus far. The dismissal of many alternatives is based on a lack of evidence for them (e.g., no tooth marks from predators). Might the missing evidence be present in those unexcavated regions?
But perhaps the biggest issue is that the argument for burial is basically an argument from ignorance. They don't provide much evidence for burial; simply rule out many alternatives. But until all alternatives are ruled out; burial isn't proven. For instance, I have a suggestion: might Homo naledi have been seeking shelter in the cave. Just like modern chimps do on hot days. Some went a bit too far in, fell down the slope and couldn't get back out.
Regardless, something very interesting is going on here. Maybe it's human relatives behaving like chimps. Maybe it's burial of the dead. More work is needed to figure out what exactly is going on though. So be excited, but don't jump on the researchers' bandwagon just yet.
References
Boyd and Silk, 2012. How Humans evolved.
Dirks, P. H., Kibii, J. M., Kuhn, B. F., Steininger, C., Churchill, S. E., Kramers, J. D., ... & Berger, L. R. (2010). Geological setting and age of Australopithecus sediba from southern Africa. Science, 328(5975), 205-208.
Dirks, P. H., Berger, L. R., Roberts, E. M., Kramers, J. D., Hawks, J., Randolph-Quinney, P. S., ... & Tucker, S. (2015). Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa. eLife, 4, e09561.
