The human family is far from a linear progression. It’s a big messy bush, with loads of offshoots. Many of which came back together with a bit of interspecies love. Well known examples of such romantic partners include humans, Neanderthals, and the Denisovans. However, a new set of skulls from China show that this may be far more widespread than anticipated. These skulls reveal a possible case of ancient interbreeding in a long dead brach of the human family.
Ancient interbreeding? More like inter-boring!
The skulls in question come from the Lingjing site, in China. Specifically the Xuchang area, from which the skulls derive their names: Xuchang 1 and 2. The site itself has been excavated for several years, revealing dozens of archaeological artefacts spread across more than a hundred thousand years of prehistory. The include faunal remains and stone tools. But the real star of the show are the Xuchang skulls. They’re notable for sharing features from many different branches of humanity.
- The inner ear shares many similarities with Neanderthals, as does the back of their skulls.
- Like modern humans, they have a more gracile skull than other hominins. This is most notable in their brow ridge (which they still have, unlike us). It’s thinner and less robust than other hominins.
- The skull is fairly low, similar to other non-Neanderthal hominins from this part of Eurasia.
This weird combination of features suggests that these fossils might be the result of ancient interbreeding. Recently in their genetic past, some of their ancestors had a bit of hanky panky with other hominins. Which is cool, as the Xuchang fossils would represent the most complete “hybrid” fossil we’ve ever found.
At the same time, that’s kind of boring too. After all, we know that interbreeding between hominin species happened. There are tonnes of genetic evidence for it. Plus, we’ve already found fossils linked to it. Long time readers might remember the Italian jaw which shared both Neanderthal and human features. Or the fossils from Romania whose DNA shows they were interbreeding with Neanderthals very recently.
Travel yourself interesting
Things start to get a bit more interesting when one considers the date of these skulls. OSL dating of quartzite from the same strata as the skull places it at around 125,000 years old. This is notable for predating the successful migration of modern humans into the region!
Genetic evidence tells us modern Eurasians are descended from a group that arrived in the region ~50,000 years ago. However, this successful migration wasn’t the first. Fossils of modern humans from around the world show some our species left Africa as early as 125,000 years ago. However, this first movement seems to have been unsuccessful, with these early migrants ultimately going extinct. These regions then seem to have been abandoned, until the successful migration that gave rise to modern Eurasians. But that wasn’t until tens of thousands of years later.
Fossils from elsewhere in China also fit this pattern. There are a few modern humans from sometime between 80 – 100,000 years ago. But these populations vanish, until a new wave of migrants reaches the region around the time genetics says they did.
This has some interesting implications for this case of ancient interbreeding. If these new fossils from Xuchang do have a human influence, then that likely came from this earlier migration. They were the only ones around at the time that could have provided it. This would mean that interbreeding between modern humans and our relatives is even more ancient and widespread than we thought. Even these early populations were getting it on with the locals.
But I suppose that shouldn’t be too surprising. After all, we did evolve from filthy monkey men.
Interbreeding is perhaps the simplest explanation for these features. And the sexiest (pun partially intended). But it isn’t the only possible cause.
It could be a case of convergent evolution. Perhaps this peculiar combination of features was beneficial elsewhere in the world, causing it to develop “accidentally”. Another explanation could be incomplete lineage sorting, a phenomena we know has been implicated in human evolution before.
As such, it is far from certain that this is a case of interbreeding. In fact, the discoverers are careful to steer clear of that messy topic. DNA from the fossils might help clear up this issue. But in the meantime, we’re going to have to apply a few pinches of salt to this idea.
Demeter F, Shackelford LL, Bacon AM, Duringer P, Westaway K, Sayavongkhamdy T, Braga J, Sichanthongtip P, Khamdalavong P, Ponche JL, Wang H, Lundstrom C, Patole-Edoumba E, & Karpoff AM (2012). Anatomically modern human in Southeast Asia (Laos) by 46 ka. Proceedings of the National Academy of Sciences of the United States of America
Li, Z.Y., Wu, X.J., Zhou, L.P., Liu, W., Gao, X., Nian, X.M. and Trinkaus, E., 2017. Late Pleistocene archaic human crania from Xuchang, China. Science, 355(6328), pp.969-972.
Liu, W., Martinón-Torres, M., Cai, Y.J., Xing, S., Tong, H.W., Pei, S.W., Sier, M.J., Wu, X.H., Edwards, R.L., Cheng, H. and Li, Y.Y., 2015. The earliest unequivocally modern humans in southern China. Nature.