In 2015 a new member of the human family was discovered. It was called naledi and might be one of the most significant discoveries ever. Their anatomy indicates it could have been an early member of our genus Homo and may be around 2 million years old.Thus, it would potentially reveal how we evolved. Additionally, the placement of the fossils hints at a deliberate burial. This could suggest ritualistic behaviour is more ancient than we imagined.
Unfortunately, life (and its evolution) is a little more complication than that. The evidence for these bones being "buried" is a lot less conclusive than initially thought. Plus, there are no solid dates for how old the fossil is; so we can't place it in its evolutionary context. We need to know how old this species is before we can really understand it.
There are still no direct dates for this species. However, a recent paper claims to have found a way around this problem; revealing Homo naledi might have lived much more recently than we thought.
Homo naledi's age
Homo naledi was discovered in 2015 by the Rising Star Expedition. Led by Lee Berger, they were impressed by how Homo naledi shared many features with earlier, ape-like species. In particular, it was remarkably similar to Australopithecus. Ultimately, Berger and his team concluded it shared more features with the Homo group; so they placed in our genus. Something I kind of already spoiled by giving the species its full name. Sorry about that.
Nevertheless, these ape-like features led Berger et al to conclude that Homo naledi was an early member of the human genus. Hence, why it still had so many archaic features. Attempts to directly date the fossil failed, but this inference about its evolution led to a tentative date of around 2 million years. This marks when Homo was beginning to take form, with Homo erectus - the first "proper" Homo - emerging shortly after this date
However, a more rigorous statistical analysis has challenged this interpretation. Another group of researchers used Bayesian analysis to study where Homo naledi fits in the human family tree. Its a complex process I won't even pretend to understand. The key point is that Bayesian analyses actually try and find the most plausible family tree by comparing them with known data. The more time a tree "wins" comparisons with alternative trees, the more consistent it is with the data and thus the more plausible it is.
When this approach is applied to the skull of Homo naledi it produces a very surprising result. Despite its apparent similarities to Australopithecus, the fossils clock in quite young. 912,000 years ago to be exact. It's basically a baby compared to the predicted date of 2 million years old.
Homo naledi in the family tree
The initial study of Homo naledi revealed something remarkable. It shared a mixture of features with both Homo and our more ape-like ancestors, Australopithecus. In fact, it shared so many features there was some discussion of calling it Australopithecus naledi; although not for long.
The Bayesian analysis of Homo naledi didn't only reveal it's age, but it's potential place in the human family as well. Like Berger, it didn't think it belongs to Australopithecus. It was clearly a member of our Homo, like us. But much like the young date of 912,000 years; it put it a lot deeper in the Homo family than Berger.
Berger placed it at the base of our genus. An early offshoot that represents what some of the earliest members of Homo may have looked like. However, this new analysis groups it in with the same bunch as Homo erectus, the Neanderthals, and us. A sister species deep in the Homo group, rather than an early ancestor "on the outside".
Time to change the changes to textbooks?
When Homo naledi was discovered it could change the textbooks. Although that depended on how old it was. Now this analysis indicates its young, is it time to revert those changes?
Not quite.
Whilst Bayesian analysis is a great tool; it's only as good as the data you feed into it. And not that much was fed into this analysis. The data for the other species came from a previous study by these researchers; which only considered a couple of different individuals from each species. We know our ancestors could be highly variable, so this definitely raises my eyebrows. Plus, they only examined the skull of Homo naledi. Many of the more archaic features are found in the body, so this would definitely bias their results.
Given these factors, I don't think it's time to label Homo naledi a baby face just yet. Nevertheless, it does serve as a reminder that we desperately need dates for this species. It shows that without them there's a huge range of possibilities for where this species might fall; hampering any attempts to properly study it.
Summary
A new analysis of Homo naledi revealed they may be much younger than originally anticipated. Although the data used in this study is lacking, it serves as a powerful reminder Homo naledi might have some surprises for us yet.
References
Berger, L.R., Hawks, J., de Ruiter, D.J., Churchill, S.E., Schmid, P., Delezene, L.K., Kivell, T.L., Garvin, H.M., Williams, S.A., DeSilva, J.M. and Skinner, M.M., 2015. Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa. Elife, 4, p.e09560.
Dembo, M., Matzke, N.J., Mooers, A.Ø. and Collard, M., 2015, August. Bayesian analysis of a morphological supermatrix sheds light on controversial fossil hominin relationships. In Proc. R. Soc. B (Vol. 282, No. 1812, p. 20150943). The Royal Society.
Dembo et al., 2016. The evolutionary relationships and age of Homo naledi: An assessment using dated Bayesian phylogenetic methods. Journal of Human Evolution
Hawks, J. and Berger, L.R., 2016. The impact of a date for understanding the importance of Homo naledi. Transactions of the Royal Society of South Africa, pp.1-4.
