I got up all bleary-eyed this morning, and before I got my first sip of coffee, the first thing I saw, blasted across Twitter and all the popular news sites, was the news that a new species of human, Homo naledi has been discovered in South Africa. They have the partial skeletons of 15 different individuals, over 1500 bones, all recovered from a single cave. They're calling it a new and unique species, and further, they're claiming that the site is a ritual burial chamber.
Whoa. Brain is whirling. This thing is all over the net, over night. Better drink more coffee.
OK, that's better.
I'm a little put off by the abrupt and sensationalist appearance in pop news sites, but here's the science paper. It's published in eLife, an interesting journal I've written about before. It's peer-reviewed, the lead authors have a respectable reputation, and it looks legit. It's a real discovery: a cache of bones in a very difficult-to-reach, sheltered site. One of the fascinating bits of the story is that the cave is so inaccessible, reached through such narrow crevices, that all the bones were recovered by a team of women who were small enough to fit.
No matter what, this is an impressive and exciting discovery. A whole small population of individuals, all found in one place? There are years of analysis waiting to be done. Here's the holotype and the large collection of bones used in the first publication. Homo naledi is a small-brained, bipedal hominin, that's for sure.
Now for my reservations.
The researchers haven't yet dated the specimens! We don't even have a guess! That's how preliminary this publication is. I can sort of understand wanting to get an exciting find like this published as soon as possible, but I have no idea where to place this species in the family tree now. Is it 3 million years old, or 300 thousand?
It's been labeled as a new species, but is it? I'm not an expert on human evolution by any means, but it looks like it fits within the parameters of Homo erectus, and the authors note its close resemblance to H. erectus, but also insist that there are small, unique features to the skull. I'd want to see more input from other experts. It's always tempting to slap a new species name on a new specimen, but I'd be just as thrilled if this turned out to be a comprehensive assemblage of a H. erectus group.
The news stories are all speculating that this is a ritual burial site, suggesting that our ancestors had certain cultural practices long before we expected. We can't say anything about the timing, because we don't know how old the site is! But there are some suggestive details. The cave is extremely hard to access (although we don't know anything about accessibility when the cave was in use), and most interestingly, only H. naledi bones are found in the cave. That suggests it was not simply a rubbish pit, or that animal remains naturally washed into it. Ritual burial seems like a good explanation, except that these people had brains the size of an orange.
Most of the coverage right now seems gushing and uncritical, but I recommend the article in the Guardian, which has a good balance of enthusiasm and skepticism. I think it's a great day for the science of human evolution, but the full details are going to take much longer and much more work to emerge. I'm looking forward to further reports. The world had better fund more anthropology/paleontology research so I don't have to be kept waiting!
The ritual burial point is interesting. Curious to know what suggests ritual above say an interest in potholing, gone horribly wrong.
First of all, the sheer ferocious courage of the women who went into that place is off the charts. Even with all the high tech, it must take nerves of steel to crawl through a space where you can barely move and who-knows-what is down there. They deserve major credit for having done the most difficult and dangerous part of this project.
Second, the point that the specimens had small brains is interesting, particularly in light of the commentary that their brains would have been too small to account for certain advanced behaviors that are being attributed to them. In recent years there has been a trend toward discovering that various animals have capabilities that are "surprising" in light of their brain sizes: pigeons recognizing themselves in mirrors, crows making simple tools and using them in three-step plans to get food, dogs and certain species of monkeys (small monkeys, not great apes, and darn if I can't remember the species) having behavior consistent with a sense of fairness, etc.
What all of those findings point to is that our estimates of capabilities relative to brain sizes are too conservative, and thus that our models of the functioning of neurons and brains are more incomplete than we have expected. This is bound to be a fruitful area of research in coming years.
Third, if in fact these findings are evidence of burial of the dead, they may suggest that the (presumably emotional, that's my hypothesis anyway) basis for death-related beliefs is also something that can operate in smaller and simpler brains than we might have expected.
Hopefully it will become possible to excavate this entire site in detail and in a manner that entails no further dangers to researchers. Whatever we discover as a result will be highly valuable to understanding our history and possibly to further work in relating brain size to capabilities in a range of species.
@G (post # 2) You make some great points regarding capabilities vs brain size. Observing animal behavior, I've often felt animals are a lot more intelligent than we give them credit for. Thanks for sharing.
What if if a large group decended into this cave to escape something and got trapped, drowned?
Don't get me wrong- I love the possibility that this is burrial site but it seems with the limited info a number of less dramatic alternative and seemingly equally plausible hypotheses are possible?
There certainly are similarities with H. erectus but also seem to be important differences. If you subscribe to the H. ergaster/erectus split then it is fairly easy to grok a new species that is this different. If you don't, then it might be a bit harder.
There are numerous cranio-facial differences, derived wrt H. erectus. There are also very important differences in the teeth. So many differences overall that my money is on this being a population that separated form erectus relatively early in erectus time and stayed separate. In other words, the cumulative differences suggest a fairly late date, to the extent that one can (with caution) track time with morphological variation. (not the best dating technique in the world)
As far as this publication being premature because of the lack of dating, that really isn't or should not be an issue here. Big picture: We have a date for this find; Pleistocene. Probably. Plenty of new species are introduced with much coarser dates (though admittedly usually much older material). But most importantly, the way SA cave material ultimately gets dated is arduous and time consuming and sometimes near impossible. It isn't like they can run some samples and get dates. The methods uses usually involve recreating the calibration new for each deposit, inventing new approaches, etc. This could take years. It would be really bad to keep a lid on this find for that period of time.
@Ajay chitnis #4: I would highly recommend reading the companion paper from the original authors, http://elifesciences.org/content/4/e09561 , which discusses the geological setting, the site excavation, bone taphonomy (how bones fossilize), etc.
Despite being a technical paper out of my field, I found it really accessible, and the terminology I didn't recognize was available on Wikipedia.
@Iain #1: "Ritual" in this context (as I've discovered) turns out to be a technical term. It doesn't have the religious connotations, but merely means some activity which is not directly practical. Art is "ritual" in this sense, unless the art is mapmaking or some such.
Pulling recently deceased bodies into a remote, isolated cave chamber, instead of leaving them far enough away from your campsite to avoid contamination, counts as "ritual" in this sense.
I can also add this about dating. The deposit in which the hominin material was found is like a lot of material found in these caves. It is not characteristic of a particular time period. One cave I excavated in nearby had similar sediment we kew to be 1.5 million years old, and that deposit contained the same sort of undiagnostic microfauna as this site. At the same time, the sediment was exposed to other sources of material and could easily contain later material on its surface. All of the microfauna was originally contained in consolidated rock-like breccia but the parts of the breccia that made it rock like had chemically disappeared, naturally, in recent thousands of years. It is possible that Denaledi is like that; million year old material that has been demineralized. Or, it is possible that demineralized sediment was later the surface on which these hominins did their thing. You can't easily tell.
Also, on the ritual part. In caves in this area you find mammals from rodents to bats they live there) to small carnivores and primates that seem to crawl into the caves and die there. I assume they are looking for shade and water, if ill and during a drought and basically dying off. There, they dry up and mummify. You see these animals frequently. I remember visiting sites with Lee and finding several such things. SO, when you look in enough of a cave system you find these dead animals, and in cases where they would be eventually covered in sediment, they may become fossils. It is thought that many of the SA australopiths are jus this.
However, first, as pointed out, one usually finds a few different species, not just one, of larger mammal. And second, you find very little of this really deep in caves .. the farther in you go the less you find. The fact that this site has many individuals and only hominins among the large mammals is very much out of sync with what is normally seen. Thus the idea that they were going in there on purpose. (with their dead?)
The way I interpreted "ritual" in this context was "repetitive behaviors associated with abstract beliefs." That's an attempt at a conservative / minimalist definition, and not too far off-target from Michael @ 7.
Greg @ 8: Very interesting alternative hypothesis (non-ritual, relief-seeking behavior close to death), with your first-hand findings in the same geographic area to back it up. I take it someone's going to examine the present fossils in light of that.
What is the likelihood that the narrowest passages were substantially larger when these proto-humans crawled into that cave? To my mind a dying person would be unlikely to be able to crawl through narrow passages unless they had a strong differential motivator as compared to seeking some other place for respite from their condition.
Something else to look at: the position of the body, limbs, etc., as compared to what is expected as an ordinary result of death. Consistently unusual positions might indicate that the bodies were placed there by others.
There are obvious religion angles to the "burial" speculation, contingent on the (questionable per Greg @ 8) inference that the present site is a burial site:
= Possible roots of religious beliefs going back to proto-humans.
= Speculation about the neuroanatomical basis of death-related beliefs.
= Comparisons to death-related behaviors on the part of currently-living species e.g.great apes, elephants, dogs, etc.
Good question on passage size. They can get bigger bit usually don't unless there is active erosion from flowing water, which does not apply here. Maybe a tiny bit bigger from spalling etc. They can get smaller and even close up from capstone formation. Worth trying to figure out.
@Greg #10: That last comment, "They can get smaller and even close up from capstone formation," I think, is one of the potentially solvable unknowns. Berger et al. didn't answer this in their companion paper, but did mention it as a way to further inquire (not answer!) the likelihood of hominids being able to repeatedly get through the complex into Dinaledi Chamber.
If the "Superman Crawl" has become narrower over time, then it would have been wider/taller in the past, and easier to traverse. Similarly with the chute over Dragon's Back into the chamber.
All 15 bodies were found perfectly laid out next to each other. The gap that they had to crawl through to get to the location was only 18cm's wide. The main archaeologist could not get to the site as he was to big. The The Chest to the Pelvis is primate like as well as the shape of the skull. However from mid thigh is (Not Similar to Human), but exactly the same as human. From elbow down is exactly the same as human, even the hands are 95% like human's, accept they are slightly like primates hand, in that they are slightly curved in.
Homo Naledi is the perfect half human half primate.
@Gareth Moore #12: "All 15 bodies were found perfectly laid out next to each other." Wait, what? Or rather, [Citation needed]
Please go read both the primary and companion papers. They describe exactly what was found, in great detail, including all of the fragments, how the fragments were distributed, and the two small articulated pieces (one hand and one foot).
#11: I think it is answerable in a number of ways.
I know of one cave that has a small number of mammals, and what looks like a bunch of baboons that maybe all came in at once and died there. But given what is covering the bones, and a few other indicators, it looks like they have been there for many thousands of years (tens of thousands?) and the cave has features that are delicate and intact, indicating that nothing has gone in or out of there for a very long time. SO there are bones in there, but absolutely no evidence of any kind of entry way (the cave was uncovered during calcite mining).
So you can get a cave to totally seal up.
What people need to appreciate is that these very complex features require a lot of careful and constructed-on-the-fly study to understand. In order to measure the time of capstone sealing, I would sample the capstone and try to calibrate thickness with time or identify specific layers. There are minerals that are found in the groundwater there for specific periods of time, but not others, owing to changes in upstream landscape development, which may provide a sort of clock, but this clock would have to be calibrated locally. There are ways of dating (maybe) the capstone deposits sort of directly (ESR, etc.). In any event, it might be possible to measure the constricting sediment/deposits' thickness and get time rate on their formation and talk about how big the various passages would be over time. This research would take about three to five years if things go well and it was well-enough funded, in my estimate.
In the mean time, a very careful study has to be done to check that there are not other passage ways. I strongly suspect Lee and his team have already looked carefully, and I'd be surprised if there were. But that's the kind of thing that could be missed, possibly. Referring back to the case above, that is a cave with an opening big enough to allow baboons in, but we don't know where the entrance is. It is presumably camouflaged behind a giant stalactite or something.
PBS did a 2hr show on H. naledi as an alternative to the candidates debate:
Entire show on video if you scroll down. No mention of 15 individuals laid out 'side by side'.