PLEASE NOTE: Based on subsequent analysis, I have changed my mind on this fossil. Please find my new thoughts here.
Social media has been abuzz with reports of a newly-discovered ancient relative of people. Named Homo naledi, this “new species” is supposed to shed light on the supposed evolution of human beings. One news report said the discovery “…may alter ideas about the human family tree.” Of course, we’ve heard that before. It seems that every major discovery related to the supposed evolution of humans is said to radically change our view of how humans came to be. While this discovery is very, very interesting, I seriously doubt that is has anything to do with people.
One of the things that makes this find so interesting is where the bones were found. They were found in a cave more than 80 meters from its entrance. Even more intriguing, the chamber in which the fossils were found was accessible only through a narrow chute. The chute was so narrow that most paleontologists couldn’t fit through it. Indeed, in order to excavate the fossils, the lead investigator (Lee Berger) had to put out an advertisement on social media. It called for “…tiny and small specialised cavers and spelunkers with excellent archaeological, palaeontological and excavation skills.” There were 57 people who answered the ad, and six women were chosen from that group. They excavated the bones, while the other members of the expedition watched on video.
In the end, the paleontologists think they found fragmentary remains of at least 15 individuals. The picture above shows a partial composite skeleton that was made from these different individuals. In one of the two scientific papers written about the find1, they say that this composite skeleton represents the remains of a new species. Why? Because it contains a lot of traits associated with the genus Australopithecus, which is supposed to be an early ancestor of human beings. However, it also contains traits that are more like those of modern humans. Because of this mix of “primitive” and “modern” traits, it is thought to be a new species in the supposed evolutionary history of people.
While there is certainly a mixture of traits found in these fossils, I seriously doubt that they belong in the genus Homo (the genus that contains human beings), and I seriously doubt they are related to us in any way.
Now please understand that I am not a paleontologist. I am not even a biologist. I am simply a nuclear chemist who has taken an interest in the creation/evolution controversy. As a result, you need to take my comments for what they are worth. Nevertheless, as I read the scientific papers, I kept wondering how the authors could claim that this is a single species or that it belongs in the genus Homo.
Let’s start with the issue of the genus. One of the major characteristics that is used by paleontologists to classify these kinds of creatures is the cranial capacity (the volume of the part of the skull that houses the brain). While there were no complete skulls found among the fossils, four partial skulls from different individuals were used to construct several possible composite skulls. Their cranial capacities were between 465 cubic centimeters (cc) and 560 cc, which are consistent with the range of cranial capacities found in the genus Australopithecus. They are smaller than the cranial capacities generally associated with the genus Homo. In addition, the skulls do not have the protruding nasal bone expected for the genus Homo.
Of course, there is more to the skeleton than the skull, but once again, most of the other skeletal features don’t line up with what we expect of genus Homo, either. Consider, for example, the femur, which is the leg bone between the knee and the hip. The top of the bone ends in a small ball that is attached to the rest of the bone by a long neck. In addition, there is a protrusion that points backwards. Once again this is very characteristic of the genus Australopithecus. A femur characteristic of genus Homo has a larger ball, a smaller neck, and a protrusion that points the other way. Similarly, the shapes of the hips and the ribcage are characteristic of the genus Australopithecus, not Homo.
So why do the authors assign these specimens to genus Homo? Partly, it is because of the feet and hands. While the curved finger bones are, once again, characteristic of genus Australopithecus, the thumb and some other details of the hand are quite different from what you expect from genus Australopithecus. However, they are also quite different from what is found in genus Homo. The foot is more like what is found in the genus Homo, but once again, the toes are curved, which is more consistent with the genus Australopithecus.
Since the vast majority of the skeletal remains are more consistent with genus Australopithecus and the few similarities to genus Homo are minimal at best, I think the assignment to genus Homo is not really justified based on the remains themselves. I actually think the real reason these fossils have been called “human-like” is found in the second paper related to the fossils.2 In that paper, the authors try to make the case that because these fossils were found in a hard-to-reach chamber of a cave, they were the result of ritualistic burial, which is a uniquely human characteristic.
This, however, is even more of a stretch. There are many possible reasons for an assemblage of fossils being found in a hard-to-reach part of a cave, and burial seems to be the least likely one. Based on the map of the cave as given in the paper, in order to “bury” the bodies in the chamber, a living individual would have to drag them while executing a complex climb in a dark part of the cave. Also, the paper clearly says that there is no evidence of trauma to the bodies, so the idea that they could have been dropped down a chute to land on the floor of the chamber seems rather far-fetched. Of course, as the authors point out, it’s possible that the cave was different back then and the chamber was easier to access. If that’s the case, however, there’s no reason to suspect that there was anything “special” about the chamber back then. Thus, there would be no reason to think that it was a burial chamber.
Here’s the other problem I have with the conclusions of these papers: it’s not clear that the fossils all come from the same species. One of the partial skulls, for example, is noticeably different from the others. It is much more rounded than the others, and it has a much higher forehead than the others. It’s hard to understand how that skull can be from the same species as the others. If there is a mixture of species in this fossil find, then the composite skeleton could also be a mixture of species, which makes any conclusions drawn from it useless.
So what does this non-paleontologist think of these fossils? Like the other members of genus Australopithecus, I think they are the remains of extinct varieties of apes. Most likely, it is a collection of fossils from more than one variety of extinct ape. I don’t see any justification for thinking they are part of a supposed human evolutionary line, and I certainly don’t find any reason to put them into genus Homo. Of course, I am not an expert in this field, so take that for what’s it’s worth.
I will leave you with a quote from an expert, however. Primate anthropologist Dr. Esteban Sarmiento wrote something in the journal Science five years ago about another supposed human ancestor that had been found. However, I think his quote applies to this find as well.3
…it is curious that in a century-old race for superlative hominid fossils on a continent currently populated with African apes, we consistently unearth nearly complete hominid ancestors and have yet to recognize even a small fragment of a bona fide chimpanzee or gorilla ancestor.
In my opinion, the reason is simple. No one wants to find a chimpanzee or gorilla ancestor. However, everyone wants to find a human ancestor!
2. Paul HGM Dirks, et al., “Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa,” eLife DOI: http://dx.doi.org/10.7554/eLife.09561, 2015.
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3. Esteban E. Sarmiento, “Comment on the Paleobiology and Classification of Ardipithecus ramidus,” Science 328:1105, 2010.
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