New Chinese hominin species: Dating

ResearchBlogging.org
When an evolutionary gaze was first cast upon humanity it was believed that we had evolved in Asia due to our many similarities with orang-utans. As such most early attempts to uncover our early ancestors focused on that region. It wasn’t until the 1960s that the focused shifted to Africa and we made real headway in our understanding of hominin evolution.

An unintended side-effect of this was that Asia, once the source of all knowledge on human evolution, got significantly less attention. As new research looks into this continent it would seem that ignoring it was unjustified and a variety of interesting were discovered. The enigmatic denisovans, Homo floresiensis and now “the red deer people.”

The latter seem to be taking the internet by storm with several papers and blogs appearing in the bast few days commenting on the discovery of these recent yet peculiar specimens. Or rather, their rediscovery. They were first excavated in 1989 in Maludong, Southern China, with further remains being stumbled upon in 1979 in the nearby Longlin cave.

However, neither of the finds were properly investigated until 2008. Then, after 4 years of research, the official verdict was in: they’re funky looking.

Unofficial verdict: Very funky looking

But the question thus becomes are they funky looking enough? The researchers claim this finds contains a peculiar mix of old and modern Homo sapiens traits with a few never-seen-before features thrown in for good measure. As such it should force us to re-evaluate the traditional model of human model into Asia.

Typically it is thought that several migrations entered Asia throughout the course of the last 100,000 years, replacing any of the previous occupants of the region. Although the interbreeding with the Denisovans and the late survival of the hobbit shows the story is more nuanced than this simple tale might suggest the general principles are still accepted, albeit with the acknowledgement that future plot twists may appear.

However, if one of the hypotheses put forwards by the scientists involved – that this represents an archaic population that survived until modern times – then this tale would have to be reconsidered even more drastically than before as this doesn’t represent some isolated island population but one that managed to survive until very recently on the mainland, in close proximity to anatomically modern humans!

Note how China isn’t an island

Their alternate hypothesis is that these finds represent an early human migration into China that retained an unusually large amount and went down a slightly different evolutionary path once it arrived. This idea is also extremely interesting as it suggests that (a) there is a lot more variability in humans than current populations might suggest, (b) this variability persisted until very recently and (c) recent branches of humanity began to evolve differently and separated from us.

However as interesting as that it it isn’t as catchy as “new species found” so most newspapers (and a certain blog) have plumped to go with that as their headline.Whilst that certainly is the maximally interesting story it is worth noting there is an alternate hypothesis that is still very interesting and just as plausible as them having discovered a new species.

But of course, for either hypothesis to be correct then the researchers would have to be correct. The finds would have to be as old as they say they are (~17,000-11,000 years old) and as strange as claimed. Are they?

Dating

At Longlin the researchers were able to get a single radiocarbon date and 3 uranium-thorium dates from the cave. 2 of the U-Th dates had to be dismissed due to contamination with the final providing a “bookend” to the site. The skeletons had to have been deposited prior to the formation of the rock they were dating (~7,500 years ago). However, knowing that the specimens are >7,500 years old doesn’t really tell us what we want to know.

The carbon date is better as it can provide an actual calendar date rather than an incredibly vague age. Further, the date provided is consistent with the U-Th information, a good indicator the date is reliable. That said it is still just a single date and radiocarbon is notoriously easy to contaminate. Without further samples to confirm its reliability I view it with more than a healthy dose of skepticism.

And all the glaring that comes associated with such skepticism

Meanwhile they have an absolute abundance of radiocarbon dates from Maludong but unfortunately no U-Th (or any other) dates against which to compare them. Lacking such outside confirmation again warrants some suspicious glaring at the radiocarbon dates, but not nearly as much as at the Longlin dates.

This is because they do all agree with each other. There’s 15 radiocarbon dates from the site and they all fit within 17,000-11,000 years ago. This accuracy is further confirmed when one realises that these dates are also consistent with their particular stratigraphic layer. All the dates from one layer of sediment are ~13,000 years ago; all the dates from another are ~16,000 etc.

So, whilst confirmation from additional techniques would be nice I feel more than happy accepting the radiocarbon dates from Maludong.

Carbon you did it again.

However, if we’re skeptical of the results from Longlin but accept those from Maludong what does that mean? Well, not that much. A lot of the specimens from Longlin are also present at Maludong so even if we dismiss the former as suspicious then we should still be able to accept the researchers’ conclusions.

A few bits of teeth are only found at Longlin (for example it contains the only premolars from this dataset) but for the most part this discrepency is minor. The biggest issue is that Longlin contains the largest complete skull fragment which may bias how researchers viewed the smaller skull fragments. This bias would be completely unwarranted if Longlin is dismissed.

But then since they provide actual data it doesn’t really matter if they’re biased – anyone can look at the dimensions of the skull and see if they really are what they say they are.

Curnoe, D., Xueping, J., Herries, A., Kanning, B., Taçon, P., Zhende, B., Fink, D., Yunsheng, Z., Hellstrom, J., Yun, L., Cassis, G., Bing, S., Wroe, S., Shi, H., Parr, W., Shengmin, H., & Rogers, N. (2012). Human Remains from the Pleistocene-Holocene Transition of Southwest China Suggest a Complex Evolutionary History for East Asians PLoS ONE, 7 (3) DOI: 10.1371/journal.pone.0031918

Continued in Part 2 ->

6 thoughts on “New Chinese hominin species: Dating

  1. I found, with a bit of luck, that Peñón Woman, from Mexico is very similar-looking in many aspects to Longlin 1. In turn Peñón Woman is not that different to a true Mongoloid skull like Peñuelas (Chile). Although indeed different enough to raise some eyebrows and throw some speculation around.

    Meanwhile the paper clearly places the other skull (vault) overlapping Crô-Magnon 1. This reminded me of my own model (outlined casually here and there) of a proto-Eurasian population with loose Caucaso-Australoid features, only gradually coalescing in each place into the modern racial types by means of internal remixing and lack of admixture at the super-regional borders/buffers like NE India or Wallacea.

    In turn I have been told once and again that Cromagnids were vaguely East Asian precisely in traits like the zygomatic (cheek) bones or the gonials, all of which may be influenced by mastication habits (and/or genetics/heritable epigenetics).

    Now with these individuals, Longlin 1 and Peñón (maybe Luzia also) we can extend that notion of Australo-Caucasoid to an Australo-Mongoloid continuum in the East which was less well defined earlier but that showed up in some scattered traits. These hyper-marked zygomatic bones would actually be exaggerated anomalies possibly at the origin of the Mongoloid phenotype (or branches of the main trunk leading to it). They seem somewhat mesocephalic but brachicephalism is another trait that must have evolved at some point (clearly not ancestral) so anything less dolicocephalic than Africans (or Upper Cave skulls) is an step in that direction.

    Also the modern Mongoloid phenotype appears to be much less homogeneous than its Caucasoid counterpart for what I’ve seen. So it’s not like a clearly defined evolutionary end has ever been reached for all the Pacific arch from Indonesia to Alaska and then to Patagonia.

    • IMO not (although I’m almost positive that some will fantasize with it). “Denisovans” are defined, as said below by their genetics. Their mtDNA widely out of the Neanderthal-Sapiens branch (possibly is H. erectus mtDNA) but their autosomal genetics is closer to Neanderthals (we still do not know the genome of Homo erectus from Asia). This leads me to think fo hybrids between Neanderthals and Homo erectus (maternal side specially), what makes sense because Neanderthals (unadmixed in principle) lived in caves just south of them.

      Also the fact that “Denisovan” admixture is only found in Australasia and some parts of SE Asia, suggests that the admixture episode actually took place in SE Asia, so “Denisovans” are just a proxy for a tropical cousin with all likelihood. Some Homo erectus are known to have lived to late dates in that area (notably the Hobbit but also H. erectus soloensis from Java, even if the dates have been pushed back a bit recently).

      I would imagine that all East Asia was thinly populated with H. erectus upon arrival of modern humans and that in some place hybridization happened. However the level of hybridization is so low even among Papuans and Australian Aboriginals (and we must discard redundant Neanderthal detected admixture, if, as I think, “Denisovans” are Neanderthal hybrids) that no traits should be apparent (<5% admixture is not obvious at all).

      The authors do claim that these people could have some erectus affinities but, if you look at the graphs, the claim is not backed at all: they are not closer to erectus than to Crô-Magnon and generally they do not step out of the H. sapiens zone, something notable for a skull with such an anomalous zygomatic bone.

  2. Difficult to say given that the denisovans are defined by their dna but there is no dna availible for this specimen.

    However, the denisovans did contribute to our modern genome whilst both of the hypotheses regarding the red deer people postulate they did not.

    So it’s a possibility but a remote one.

  3. Reblogged this on pondering the universe and commented:
    This is an fantastically written post on an awesome topic, I read an article on this in BBC new a few days ago on. Bone and teeth fragments were found in a cave in southern china back in 1989 but only recently studied. Truly an awesome revelation, if the dating is correct, this species would have possibly coexisted during a time period with modern homo sapiens! Go a head and give it a read! theres plenty of interesting posts on this this blog, i suggest you check it out.

  4. Pingback: Feather Denial « Eye on the ICR

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