Homo naledi is the newest member of our genus (Homo) to be discovered. And ironically, it might also be the oldest; although it has yet to be reliably dated. However, one new thing about it is how it's being researched. Normally all the data is published in one big lump at the end. However, this time researchers are trying to give updates as they go. And I'm trying to do the same thing.
Last week I talked about some new research on their skull. The discoverers revealed it's unique, but still definitely belongs to our genus. They also announced the discovery of a new juvenile of Homo naledi. Or rather, they recognised that one of the bones they found before is a separate juvenile specimen.
This week we're moving down the body a bit and looking at their arm. In keeping with their new research approach, this has already had some data published about it. And now they're updating it. The resulting information on the arm doesn't quite seem right. So what's going on with Homo naledi 's weird arm?
I feel it in my fingers
When Homo naledi was first discovered it was notable for not being particularly notable. It had many of the features you would expect for an early member of our genus. It was bipedal but had a small brain. Its legs looked quite modern, but its arms didn't. It all fit in quite nicely, assuming that they really are the early member of the genus they look like. As I mentioned, they haven't been dated yet.
However, there were a few exceptions to this "expected" trend. One notable one being their hand. The earlier genus, Australopithecus, seems to have been a tree climber. And their arm was well suited for it. For the most part, Homo naledi inherited this ape-like climbing arm. Even the hand seemed well adapted for climbing, featuring long curved fingers great for grasping branches.
But as I said, the hand was weird. Whilst some parts, like the curved fingers, looked old-school other parts seem a lot more modern. The thumb, for example, is thick and strong; a lot like ours. This is a great adaptation for manipulating stuff and using tools. Not so great for climbing, which is weird given how well suited to that the rest of the hand is.
The other "weird" part of the hand is their wrist. I put weird in quotemarks because it isn't actually that unique. It's actually quite similar to ours and other later members of Homo. Which isn't what you'd expect for an early species, adapted for tree climbing.
Homo naledi and the strange shoulder
On the other hand (pun totally intended) the arm is a bit more consistent with both itself and what's expected of it. This update provides further information on the arm. And it confirms this pattern.
The rest of the arm seems to be fairly well adapted for tree climbing. It's similar to those earlier Australopiths like Lucy and distinct from later Homo in many key ways. Notably, the shoulder is orientated slightly more upwards than in modern humans. It was thought that this helps hold the arms over the head, good for dangling below trees and swinging from branch to branch. However, new evidence is challenging this view. Nevertheless, it is clearly a common trait in climbing species.
In short, this update reinforces the weird pattern documented during the discovery. A combination of tool-using traits and climbing traits. A few years ago this contradiction would be downright paradoxical. However, recent discoveries are suggesting that tool use evolved earlier than we thought. The Lomekwian is a stone tool industry made by Australopithecus. Perhaps that kicked off hand evolution, which continued with Homo naledi.
This does seem to be the best explanation. Whilst the Homo naledi shoulder does point upwards, it's also angled slightly forwards. The result is that their arm had fairly unrestricted movement around the front of the body. Which is where' they'd be using tools. A similar pattern is seen in early Homo erectus, and we know they made tools.
Of course, this is all slightly circumstantial. The real clincher would be finding tools associated with the fossils. Which is unlikely, since the site discovered isn't a habitation site. It's something far more interesting.
Homo naledi. The palaeoanthropological gift that just keeps on giving. . . mysteries! But I shan't complain too much. It keeps giving me stuff to write about after all.
References
Feuerriegel, E.M., Green, D.J., Walker, C.S., Schmid, P., Hawks, J., Berger, L.R. and Churchill, S.E., 2017. The upper limb of Homo naledi. Journal of Human Evolution, 104, pp.155-173.
Kivell, T.L., Deane, A.S., Tocheri, M.W., Orr, C.M., Schmid, P., Hawks, J., Berger, L.R. and Churchill, S.E., 2015. The hand of Homo naledi. Nature communications, 6.
Laird, M.F., Schroeder, L., Garvin, H.M., Scott, J.E., Dembo, M., Radovčić, D., Musiba, C.M., Ackermann, R.R., Schmid, P., Hawks, J. and Berger, L.R., 2017. The skull of Homo naledi. Journal of human evolution, 104, pp.100-123.
Marchi, D., Walker, C.S., Wei, P., Holliday, T.W., Churchill, S.E., Berger, L.R. and DeSilva, J.M., 2017. The thigh and leg of Homo naledi. Journal of Human Evolution, 104, pp.174-204.
Williams, S.A., García-Martínez, D., Bastir, M., Meyer, M.R., Nalla, S., Hawks, J., Schmid, P., Churchill, S.E. and Berger, L.R., 2017. The vertebrae and ribs of Homo naledi. Journal of Human Evolution, 104, pp.136-154.
