Human Genesis

In September of 2015, Lee Berger and his research colleagues announced to the world a new species of hominin they called Homo naledi.  The remains of Homo naledi were found in a cave chamber (the Dinaledi chamber) in the Rising Star Cave system right next to the famous Swartkrans and Sterkfontein deposits in South Africa.  As is typical with new discoveries, members of the media stirred up some contrary opinions about the team’s conclusions, but this time, there was a great deal of genuine skepticism of one of their claims.  Berger’s team argued that Homo naledi intentionally disposed of their dead in the remote cave chamber in which they were discovered.  Some understood them to say that Homo naledi engaged in ritual burial, implying a complex behavior like we do today, but all it really needs to mean is that Homo naledi consistently dumped the bodies of their tribe members in the same place.  I think it’s important that we do not read too much into their claims.  No one thinks this is a fancy burial like modern humans do.

So why do Berger and Co. think Homo naledi disposed of their dead in this cave?  The Dinaledi chamber and the remains of Homo naledi have some peculiar characteristics.  Any theory explaining the presence of Homo naledi in the Dinaledi chamber will have to explain these things:

1. The bones are surprisingly concentrated in a very small chamber of a much larger cave.  No Homo naledi bones outside of the Dinaledi chamber were recovered, but in the chamber, the bones were very common.  However Homo naledi got to that chamber, we would have to explain their high frequency in the Dinaledi chamber and their absence from the rest of the cave.
2. The Dinaledi chamber is very inaccessible.  The scientists that excavated the bones required a one-way trip of two hours of crawling and climbing to get in or out of the Dinaledi chamber.  The chamber itself is separated by a huge rock (the Dragon’s Back) from the rest of the cave.  The chamber where Homo naledi bones are found is only accessible by climbing about ten meters up the Dragon’s Back and then over the other side.
3. The Dinaledi chamber contains mud and other deposits derived primarily from the chamber itself.  There is no evidence of catastrophic flow or flooding in the chamber.  Such deposits would leave very telltale signs in the muck, all of which are absent.
4. There is evidence of water in the Dinaledi chamber, including marks on the wall that reveal changes in the water table.  There is also flowstone on some of the deposits that contain the bones.  In addition, the bones show breakage and staining consistent with changes in water and humidity.  The water table never topped the Dragon’s Back.
5. Extensive survey and scanning of every part of the cave did not reveal any other entrance.  To see some of the beautiful laser scans of the cave, see this page from 3D Laser Mapping.  A survey of the surface together with ground penetrating radar did not reveal any other entrance to the Dinaledi chamber than going over the Dragon’s Back.
6. Other than a few recent bird and rodent bones, only Homo naledi bones have been recovered thus far.  Other cave deposits from South Africa typically contain more than just hominin bones.  For example, if there was a sinkhole at one point, then it could trap animals just as easily as hominins.  Likewise for the lair of a predator, which would eat more than just hominins.
7. Of the thirteen remains for which an age could be estimated, six were juveniles.  Finding that many young individuals is more reminiscent of a cemetery than a sudden burial of a living population.
8. The bones were generally quite clean.  They showed no evidence of weathering, as if they had originally died and decomposed on the surface exposed to the elements.  They showed no evidence of gnawing, which suggests that there were no carnivores chewing on them.  They did show evidence of invertebrates nibbling on them, suggesting that beetles or snails might have cleaned the meat off the bones.
9. The bones were remarkably well preserved.  Even the tiniest foot and hand bones were found in abundance, and many sets of bones were found in articulation (meaning that the bones were arranged as they were in life).  Articulated elements include at least one hand, multiple feet, and numerous other skeletal elements.  It is as if whole body parts were placed intact in the cave.
10. The bones occur in multiple parts of the Dinaledi chamber, implying that they were deposited over time rather than in a single event.

At first glance, we can think of a number of explanations for how these bones might have ended up in the remote Dinaledi chamber, all of which are discussed by the researchers in their paper describing the cave and bones.

• Catastrophic burial by a flood that washed the bones into the chamber.
• Mass death event – maybe they were chased into the chamber, got lost, and starved.
• Carnivore activity – some animal dragged its kill back to the cave to store or eat
• Deathtrap – the cave was once near the bottom of a sinkhole, and animals just fell in
• They actually lived in the cave, and somehow died and were buried there
• Deliberate burial or body disposal – someone or something put them there intentionally

All of these explanations also have implications that might not be part of the set of ten evidences, but we’ll get to those implications after we figure out which one is most likely.  First, let’s see how these different explanations stack up against the evidence.  Here’s a little chart to help you keep track of everything.  In the chart, I’ve noted which evidences are definitely explained by a theory (YES), and which evidences are definite contradictory to a theory (NO).

Taking them one at a time, there is no evidence for a catastrophic flood in the Dinaledi chamber (see evidence #3).  Plus, the bones were deposited over time (evidence #10), both of which mitigate against some sort of catastrophic burial.

The idea of a mass death seems appealing, but it would be hard to reconcile with the depositing of skeletons over time rather than all at once (see evidence #10).

Carnivores are definitely known to accumulate bones, but in this case, it’s hard to imagine how carnivores would leave behind no evidence of gnawing (evidence #8) or why they would kill and eat only Homo naledi (evidence #6).  The extreme remoteness of the chamber would also argue against carnivores depositing the bones there.  It’s hard to imagine a wolf or lion dragging a carcass more than a kilometer underground, then climbed up and over the dragon’s back.

The sinkhole idea makes a lot of sense, since that’s a common way to collect fossils.  Creatures that fall into the sinkhole either die on impact or starve to death, and their skeletons are preserved in the cave deposits.  In this case though, the Dinaledi chamber is not at the bottom of a sinkhole, and there is no evidence of any other entrance to the chamber (evidence #5).  In addition, it’s hard to imagine a sinkhole that only traps Homo naledi (evidence #6) and has no evidence of debris falling in from the outside (evidence #3).

So that leaves intentional burial, not necessarily because burial makes perfect sense but because everything else makes much less sense.  After all, it is really hard to imagine why Homo naledi would crawl so far underground to bury their dead.  If they did access the cave, they must have been able to use fire well.  They must have advanced beyond just making a fire to making functional torches or lamps.  The fact that these bodies were deposited over time even suggests that there was a cultural transmission going on: Older Homo naledi must have taught the younger ones where to take dead bodies and how to get into the Dinaledi chamber.

As mentioned above, the intentional burial hypothesis (or “body disposal” as Lee Berger prefers) was met with a lot of resistance.  Some objections were really sort of condescending by suggesting that the researchers really hadn’t done a good job.  People suggested that they missed “the second opening” to the Dinaledi chamber, which is disrespectful.  Other objections were just ignorant.  Armchair speculators said, “Maybe they got transported by water into the Dinaledi chamber,” an idea that we really can rule out completely, since there’s no evidence of those kind of deposits in the muck of the cave.  Other objections were little more than incredulity – how could something with a brain the size of an orange exhibit such an “advanced” and complicated behavior?  Personal incredulity isn’t necessarily a compelling argument, though.

Far more interesting in this regard is an article published in Journal of Human Evolution by Aurore Val.  Unlike the speculations, Val’s article was peer-reviewed, which makes it quite a bit more thought provoking.  She makes a number of objections that are well worth thinking about.  To begin, her intention was to “argue that, with the current state of knowledge, it is not possible to demonstrate that complete hominin bodies were deliberately disposed in or at the entrance of the almost inaccessible Dinaledi Chamber.”

Val claims that geologically we should expect that the Dinaledi chamber underwent a lot of change and did not remain unchanged since the Homo naledi ended up in the Dinaledi chamber.  Val argues that the “Facies 1b” layer of mud in the Dinaledi chamber supports her interpretation.  Dirks et al. describe Facies 1b as a mudstone with thin layers of sand and “abundant mammal microfossils.” Val claims that the micromammal fossils could be the result of owl pellets, which suggests that there is an entrance closer to the Dinaledi chamber.  Her idea doesn’t really explain why there is no evidence of a large entrance found in the ground penetrating radar survey, the interior laser scanning of the cave, or the surface survey.

Her next objection is essentially one of incredulity regarding Homo naledi crawling that far underground to bury their dead.  She brings up all the logistical challenges that would entail, and she makes a compelling point.  It is indeed very surprising to think of this cave as a practical burial chamber.

She then raises a series of concerns about the methods employed to study the Homo naledi bones.  One peculiar idea was the notion that somehow we don’t really have enough Homo naledi bones to make any substantial claims about whether or not something chewed on the bones.  She calculates that we’ve only found about 10% of the bones from the bodies of fifteen different individuals, and so concluding that they don’t have tooth marks is premature.  While it must be noted that we haven’t found any bones with tooth marks on them YET, it seems strange to argue that we really should refrain from making conclusions based on the large number of bones that we do have.  It does seem rather peculiar that none of the 1550 bones had any obvious evidence of gnawing.

Val also questions the microscopic tracks on the bones interpreted to be the marks of invertebrates like beetles or snails.  She notes that the researchers did not report any remains of these invertebrates and that invertebrates that chew on bones today are mostly surface dwellers.  This argument would only have force if Dirks et al. actually tried to connect the microscopic marks to a specific type of beetle or snail.  Since they noted only the general resemblance to invertebrate marks, I’m not sure why there couldn’t be some creatures that made the marks in the cave (and not on the surface as Val wants to argue).  Perhaps they were carried into the cave vicariously on the dead bodies.

Thus, though Val’s arguments are more thoughtful than other skeptical, off-the-cuff comments, they are not entirely convincing.  She seems to really favor the idea that there was another opening to the Dinaledi chamber into which the Homo naledi remains were transported, but the researchers who have done extensive work on site report no such evidence.

In the end then, it seems that intentional burial, as surprising as it is, is the most likely explanation of how these creatures got in this cave.  Until someone comes up with a better explanation that accounts for all of the evidences above, the burial hypothesis will continue to be favored.

For further reading on the burial of Homo naledi, see the following articles:

Dirks et al. 2015. Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa. eLife 4:e09561.

Randolph-Quinney. 2015. A new star rising: Biology and mortuary behaviour of Homo naledi. South African Journal of Science 111(9/10):a0122.

Val. 2016. Deliberate body disposal by hominins in the Dinaledi Chamber, Cradle of Humankind, South Africa? Journal of Human Evolution doi:10.1016/j.jhevol.2016.02.004.

Wise. 2016. Paleontological Note on Homo naledi.  Journal of Creation Theology and Science Series B: Life Sciences 6:9-13.

 

Todd Charles Wood