Friday, November 18, 2011

Julien Riel-Salvatore on Neanderthal Assimilation To Modern Humans

The Denver Post is hyping a new finding by hometown Neanderthal expert Julien Riel-Salvatore (author of the blog "A Very Remote Period Indeed" in the sidebar), which shows how Neanderthals could have been wiped out as a species simply by admixture with modern humans who had superior population densities.

"Neanderthals were not inferior to modern humans," said Julien Riel-Salvatore, assistant professor of anthropology at UC Denver and co-author of the study published in Human Ecology.

"They were just as adaptable and in many ways simply victims of their own success," he said. . . .

Riel-Salvatore said the new computer model takes the added step of showing how Neanderthals and homo sapiens roamed farther afield than assumed.

The computer models ran for 1,500 generations, following estimated samples of humans and Neanderthals roving across the two continents.

"You set some baseline parameters and see how these 'agents' interact," said Riel- Salvatore, who co-wrote the study with C. Michael Barton of Arizona State University. One parameter included researchers' knowledge that the last ice age forced Neanderthals and humans to widen their search for food.

They interacted, and because there were far more humans, over time that species diluted Neanderthals until they appear as just a fraction of our DNA.

Evidence of Neanderthal prowess as mates follows a March study co-authored by CU-Boulder, showing Neanderthals were experts at keeping fires burning continually. That skill, key to flourishing, had previously been thought beyond their reach.

"It shows you don't need to depend on the old cliches to explain the disappearance of Neanderthals," Riel-Salvatore said. "You don't need to make assumptions about them being stupid or less flexible."

I have two main criticisms of Riel-Salvatore's take on the matter.

First, the absence of any Neanderthal Y-DNA or mtDNA despite the fact that 1-4% of autosomal DNA in modern non-Africans has a Neanderthal source does not support the kind of admixture dilution model that he is proposing. You need a very specific kind of admixture that takes into account factors like differences between hybrid fertility and intraspecies fertility to get the observed result, and you also need to take into account post-Neanderthal replacements of much of the modern human population of Europe to make the geographic uniformity of the Neanderthal percentages fit what is observed. Also, there is pretty solid evidence to indicate that there were no significantly mixed Neanderthal-modern human communities; tribes from the diifference kinds of hominin mostly kept their distance from each other. There is not a single case of a Neanderthal skeleton and a modern human skeleton buried in the same graveyard in the same culturally continous time frame, although there is evidence of modern humans using caves previously inhabited in prior eras by Neanderthals.

Second, there is a quite strong case to be made that Neanderthals, while more sophisticated than Homo Erectus, for example, were not the intellectual equals of modern humans. Their material culture remained stagnant for 200,000 years, while modern human technologies evolved continuously and at a much higher rate. Some of the technological advances attributed to them during the contact period with modern humans (e.g. the Uluzzian) have been determined to very likely have been modern human tool cultures, and in the cases where there was change in Neanderthal tool culture, the change was probably in lower quality imitation of modern humans and didn't happen until contact took place. Their food sources were much less diverse (they were pretty much exclusively apex predators while modern humans had more fish, although Neanderthals did some non-harpoon fishing, more small game, and more fruit and vegetable gathering). Their geographic range was much narrower (they didn't make into Southeast or East Asia, nor did they make it to Africa, and they had a more limited presence in the far North and Siberia although there are some traces of them in parts of these places). The quantity and quality of Neanderthal artistic expression and symbolic activity was a pale shadow of that of modern humans (they had simple burials but no elaborate paintings or sculptures). The range of materials that Neanderthals used in tools was smaller (e.g. they used far less processed bone and twine). They had less of an ecological impact on megafauna than modern humans, suggesting that they were less successful hunters. Their social groupings were smaller from a quite early point.

You may not have to make assumptions about Neanderthals being stupid or less flexible than modern humans to explain their demise. But, despite having relatively large brains, and genes that would have given them more language abilities than some of their hominin predecessors, there is ample evidence from the material culture that they left behind that they were not as adaptable as modern humans. And, if one can determine that from independent evidence, it isn't unreasonable to include that in models of how Neanderthals went extinct.


Maju said...

I also think that there is a lot of wishful thinking.

Julien Riel-Salvatore said...

Andrew -
Thanks for the post - glad the coverage is prompting some reaction. Not to be flippant, but I think you miss the main point here. In actuality, it IS a big deal to demonstrate that even with no behavioral and genetic advantage by modern humans, Neanderthals could still have disappeared as a recognizable population. You can't question that there is a shift in mobility in both populations over time, towards increasing range sizes. That being the case, it is important to investigate what the effect of this on genetic and cultural systems could have been.

To answer your specific points:
1) "You need a very specific kind of admixture..." Fair enough, but that wasn't the point of the paper. We're not arguing that our results match those results precisely. Rather, we're saying that they provide an explanatory pathway to start investigating this.

2) "pretty solid evidence to indicate that there were no significantly mixed Neanderthal-modern human communities": only if you depend on what is ultimately an antiquated binary view of human variability in the Late Pleistocene, where hominins are classified as either Neanderthal or modern human. In actuality, what we have by and large for the period 45-30kya are archaeological assemblages, the link of which to biological entities is highly questionable, no matter what a superficial reading of authors like Mellars might suggest.

3) "tribes from the diifference kinds of hominin mostly kept their distance from each other": there is no evidence for this, I have no idea what you're basing this on.

4) "not a single case of a Neanderthal skeleton and a modern human skeleton buried in the same graveyard in the same culturally continous time frame": so what? outside of Saint-Cesaire, there are no UP burials until the Gravettian. By the simplistic reasoning you use in the next sentence (caves later used by modern humans), this means Neanderthals and Gravettians were more 'modern' than whoever made the Aurignacian (which remains an open question).

5) "material culture remained stagnant for 200,000 years": again, not true. Coloring materials, ornaments, systematic small game and sea resource use, shifting mobility strategies, clearly separated activity areas within sites, systematic control of fire, long-distance raw material procurement, and burials are all associated with Neanderthals. Pretending this isn't the case by quoting authors who ignore this evidence doesn't mean this 'inconvenient' evidence isn't there. This is hardly what I would call monotonous.

6) "very likely have been modern human tool cultures...": this is very debatable. The new study by Benazzi doesn't resolve this issue - as I've said all along, two milk teeth do not allow us to make a strong species-level attribution of the Uluzzian, let alone transitional industries as a whole. Expect to see more stuff in press about this shortly, but try to keep a more open-mind about the nature of the evidence instead of just latching onto what fits your preconceptions about how the Middle-Upper Paleolithic transition played out. As I've said, at this point, it's much better to try to figure what people were doing with these tools as opposed to obsessing about authorship and not realizing that these industries weren't efforts in bio-cultural self expression, but rather tools used in survival. Plus, as I've also said in press repeatedly, while there are some very interesting features of the Uluzzian that arguably make it look 'modern', there are tremendous differences between it and both the Mousterian and proto-Aurignacian that can't simply be glossed over.

Julien Riel-Salvatore said...

part 2:
7) "Their geographic range was much narrower (they didn't make into Southeast or East Asia": if you think of Neanderthals as a regionally specific population, this is to be expected. Plus, it's not so much the range that matters as the kinds of ecosystems they were occupying: from the Mediterranean to the Arctic, from coastal plains to high mountains (occupied for the first time) - not to shabby when you actually think about it.

8) "they had a more limited presence in the far North and Siberia although there are some traces of them in parts of these places": again, so what. By that reasoning, Aurignacian people should be less cognitively capable than the Gravettian. This is pretty spurious.

9) "they used far less processed bone and twine": does that speak to monotony or a toolkit well-adapted to their needs? As for twine, there is hardly any evidence of it before the Gravettian, and even then, much of it is indirect.

10) "less of an ecological impact on megafauna": what evidence do you have of this? Neanderthal have been shown to overexploit certain gazelles in the Near East; in contrast, modern humans are overexploiting small game and shellfish colonies by the Late Upper Paleolithic. Again, it seems you're generalizing from the UP as a whole, and not looking at the critical time period, which should be the transition itself.

11) "You may not have to make assumptions about Neanderthals being stupid or less flexible than modern humans to explain their demise." Well, doesn't that say something fairly important about how we might need to recalibrate how we think of this process?

12) "they were not as adaptable as modern humans": you try to live in Ice Age Europe with stone tools and tell me how you do ;) All joking aside, the geographical range of Neanderthals suggest they were quite adaptable indeed, as does the wide range of resources they used. If modern humans were so much more adaptable, why did they not settle more temperate latitudes until 45-40kya? If you think about it, they seem to stick to ecosystems that were fairly warm and productive. The real challenge in the Pleistocene was to survive in Eurasia, not the sub/tropics. That the Neanderthals did - and for such a long time - tells you a lot about how 'adaptable' they were.

Much of what this paper is about concerns how we look at the record, not an actual explanation of it. That's not the point of models - their goal is to generate test expectations based on hard data as opposed to the traditional, more inductive approach that continues to dominate in paleoanthropology. If you PM me, I'll be more than happy to send you a pdf of the paper and SI should you (or Manu) wish to read it.

Maju said...

Julien, you have very good points about Neanderthal reality and I have no doubt that you know all that much better than Andrew or me (I'm no Neanderthal basher). But the bulk of the hypothesis has no evidence to support it: that Neanderthals and modern humans admixed (to any level beyond anecdote) in Europe (or West Asia after the well known OoA episode that left a mark in all the Eurasian genomes almost identically, per Green, Paabo, etc.) is not proven or even suggested by anything.

Neanderthals were probably at our cognitive level or almost or even higher. In truth I could not care less: the Tuniit were also at similar cognitive level to that of Inuits and even had some technological advantages initially... But the Inuits took over the American Arctic and the Tuniit went extinct, apparently without leaving much of a genetic legacy among the Inuit (per the genetic analysis performed on a Dorset culture individual some years ago).

Hunter-gatherers displace each other with some ease, sometimes to extinction (if there's nowhere else to go, as happened with the Neanderthals and the Tuniit, probably with some climatic help). It may have have happened also to some H. sapiens groups in Europe and elsewhere later on.

Your claim is that Neanderthals live in us. True (to a small extent) but not because of any admixture that happened in the process of colonization of West Eurasia c. 48-40 Ka ago but because of an earlier admixture event at the time of the migration from Africa to India.

It is a practical impossibility that the population that migrated westward from South Asia and colonized West and Central Asia, Europe and probably parts of North Africa as well, the Western population that displaced Neanderthals and that is our common ancestors, could retain (after all that conjectural admixture you claim) only as much Neanderthal blood (or even less) as Chinese or Papuans.

Sorry, there is no way. I know that some argue for eventual replacement of that admixed population with the Neolithic but the Neolithic of West Asia was created by the same Western population (rooted in the same colonizing front of 40+ Ka ago in any case).

This Western people went to all the areas known to have been inhabited by Neanderthals: Zagros, Palestine, Syria, Altai, Caucasus... and Europe and replaced them there in a lengthy and somewhat mysterious process (but with bouts of hyperactivity, notably the Aurignacian explosion) and they show no more Neanderthal genetics than Hu Jingtao or the Dalai Lama.

So where is your alleged admixture in the modern population which is, beyond reasonable doubt, descendant of those Westerner Eurasians who displaced and replaced the Neanderthals.

I'm anyhow interested in the fine detail and therefore in the paper as such, so I'll drop you a line in hope of reading it. As always, thanks for being so open with your time and work.