Wednesday, 1 February 2012

Palaeoanthropologically Speaking (Revised): Neanderthal Genome is No Guarantee That We Interbred, with Belated Apologies to Marco Langbroek and Svante Pääbo


'I disapprove of what you say, but I will defend to the death your right to say it.' 
~Evelyn Beatrice Hall (1868-post 1939)* 
1896 Alfred-Pierre Agache--L'Épée (The Sword). A portrait of Evelyn Beatrice Hall. The Latin motto is translated 'on behalf of justice.'
That's a thrilling way to start! Don't you think? A most handsome woman, our Ms. Hall. And an eminently quotable one. On top of it all, a darned good impression of a Pre-Raphaelite painting. Awe. Some.


Now, to business. I trust that I'm not flaunting blog etiquette (or worse) by bringing up for discussion a comment that Marco Langbroek left in regard to my previous post: 'Clone a Neanderthal?' I'm extremely grateful for his comment. He's the first serious detractor to chime in since I began this project almost four months ago. This tells me that I'm getting through to the Very Serious Archaeologists. That's gratifying. 
    I can imagine that there are many more in the anthropological community like him who, upon reading or hearing of my post on cloning Neanderthals, will have muttered something like 'Pish-posh,' or 'Don’t be a silly goose,' or 'Gimme a break, dude,' or possibly even 'Hogwash!' 

     I'm hoping to use Dr. Langbroek's comment as a reason to opine upon the recent DNA genome sequencing that's spurred claims that Neanderthals and modern humans at one time interbred. 
[By the way, aside from being dramatic in a way that I couldn't have predicted until I found that beauty of an image, I intended the epigraph to assure Dr. Langbroek that this will be a civil take-down. I have every intention of following through on that promise. I trust that you'll stop me if I start to get out of hand.]
     And, because it's always best to know your opponent before you stand back-to-back and start pacing away from each other, I'd like to say that I'm in complete agreement with Dr. Langbroek when it comes to the motivation for his own major research project, 'Neandertal Living Space: the organisation of living space and the use of landscapes in Neanderthal society.' [You can see the entire document by clicking here, then click on research synopsis, about mid-page.] In his own words,
Neandertals might have had their own ... ways of doing things, which are "invisible" if one uses models from modern ethnography only as 'templates' to understand the structure of the Neandertal archaeological record. It is for this reason that Neandertals are so difficult to force into the existing frameworks. Very complex Neandertal behaviour might be hidden in the archaeological record, because our current methodologies which are heavily leaning on ethnocentric frames of reference do not allow to detect such Neandertal idiosyncracies. This situation is remarkable, as it should be these behavioural idiosyncracies, rather than just their brow ridges and lack of chin or perceived inferiority or similarity, which actually make the Neandertal identity. Certainly from an archaeological perspective.
I couldn't agree more. 
     On the other hand, I can't help but see Langbroek's problem statement as a paraphrase of a notion that I've been struggling with for some time. Neanderthal behaviour could well be incommensurable from a modern human point of view---literally not understandable, because we can't conceive of the possibilities. And while I agree with his motivation, I think he may already have doomed himself to a sterile research result. Why? Because he'll begin from the assumption that Neanderthals are every bit as human as you or I--which means the proposition for which he seeks support in the archaeological record is assumed in the premise. This is another example of petitio principii, the logical fallacy known as begging the question. 


You'll see in a moment that he's as certain as anyone could be that the Neanderthals were every bit as human as you or I. How then does he propose to recognize characteristically Neanderthal use of space when he already assumes that they gave meaning to their spaces in the same way that you or I do? He'll be chasing his tail. 
[But that's for him and those who'll referee his attempt to publish the results. If, and I strongly doubt this, those referees were to decline publication for the reasons I've outlined, what then? I can say one thing for certain. The agencies that have funded this research based on his proposal will have serious denatured avian protein on their faces.] 
Finally, to the meat of this essay. I came here to tease out what's implied in Langbroek's comment on my last post. 
     It reads as follows
We don't need to clone a Neandertal in order to know if Neandertals could hybridize with Homo sapiens. We already know they can, and did. Each current Eurasian has 2% to 4% of Neandertal genes as a result of hybridization 40-60 ka ago.It is therefore interesting that you state: "think of what that hybrid might turn out to be like". Well, I can tell you: more like us than you might think. After all, me, typing this, and you too, are a 2% to 4% Neandertal-sapiens hybrid. So, are "they" really that much different from us then, per your suggestion? I doubt it.And that is exactly a reason why we shouldn't clone them. But with regard to hybridization with such a clone product: we already have been there and did that, during the Pleistocene. And kept hybridizing with the offspring, to the point that nowadays each and every Eurasian person has Neandertal genes in him or her. This wouldn't have happened, if "they" were really that animaline.
The DNA evidence that Langbroek is referring to, among others, is the work of Svante Pääbo (justifiably famous for sequencing the Neanderthal genome). Dr. Langbroek's comment implies, nay proclaims, that Pääbo's conclusions are solid gold. I have a problem with any proclamation of that ilk [as you might imagine]. While Pääbo's genomic work might well be sterling (and I have no doubt), his arguments leave a lot to be desired.
     Briefly, once he had a 'draft' of the Neanderthal genome, Pääbo compared it with the genomes of four (yes, 4) modern humans from four widely separate parts of the globe. The one African chosen, a Kalahari San person from the very south of that continent, a
pparently doesn't share the same genetic synapomorphies that three other modern human individuals share with the Neanderthals.   
     Working from the fossil evidence Pääbo knows that the ancestors of the Neanderthals left Africa some time between about 600 and about 400 kya (i.e. Homo antecessor or similar). Then, again based on the fossil record, Pääbo concludes that a quasi-identical population stayed on in Africa, and that, as the genomes in Europe and Africa diverged, the African holdouts became skeletally modern. Moreover, on the best evidence thus far, there's no record of those modern-ish Africans outside of Africa until about 100kya (e.g. at Qafzeh Cave, in Israel). Thus, evolution worked its magic on the geographically isolated genomes of the Neanderthals and skeletally modern humans for upwards of 300 ky. 
     Pääbo has presented evidence that Neanderthals and present-day humans share a portion of their genome that neither species shares with the present-day, single individual who provided the DNA from South Africa. Pääbo's argument, therefore, comes down to this: the skeletally modern humans didn't leave Africa with the apomorphic genome. Ipso facto, presto change-o, they must have acquired the apomorphic genome after they, too, left Africa. And if they didn't leave Africa with the apomorphic genes, they could only have acquired them through interbreeding with the Neanderthals. Brilliant! Case closed! Nobel Prize! 
    Not quite.
    See. Here's where it gets sticky. And this is why this business of ours is so bloody hard to do really good work in--you have to sift through a lot of uncastrated bovine excrement to get to a narrative of the way things more than likely 'went down,' palaeologically speaking.
     Sticky point #1. Africa is, what, 9,500 km from north to south? Imagine, in a time before there were people like us, there were antique humans all over the African continent. What are the odds that they all share a common genome? Slim and none, I'd suggest. How many genetic bottlenecks would it take to produce a mini-genome divergence in a more or less widely distributed population of the same species? Not many, I'd suggest. Pääbo and his followers have placed a great deal of faith (and faith alone--no scientifically valid evidence is produced) in the assumption that the present-day southern African stands as a model for all of the descendants of what would have been a northern African sub-population of the hypothetical pan-African species that gave rise to both the Neanderthals and modern humans (skeletal or behavioral).
     Sticky Point #2. The timing of the putative hybridization. Pääbo's theory is based on the assumption (there's that word again) that the Qafzeh hominids were like us. They weren't! They were behaviorally identical with the Neanderthals. Their technologies were the same. All that modern humans share with them is the appearance of their skeletons. So, presumably, a hundred thousand years or so ago, some skeletally modern, technologically Middle Palaeolithic hominids met up with some Neanderthals with the same behavioral appurtenances. Et, voila! Little hybrid babies. A beautiful and emotional ending to an epic story that spans hundreds of thousands of years. The families were united again, at last. Why is that news? It'd be a different story if African ex-pats 50 or so kyr ago were to have done the same thing. At least by then we can be fairly certain they and we were cognitive equals.
     Unfortunately for Pääbo and Marco Langbroek there's no way to be certain that the Qafzeh hominids were anything like modern humans, on the evidence. And as you all know, the technology employed by that species and the Neanderthals is alien to modern humans. What all that means about the cognitive abilities of Middle Palaeolithic hominids is still, alas, unresolved.
     So, bottom line. Pääbo and Co.'s scenarios are plausible. But plausibility isn't enough on which to hang a claim the magnitude of the one that says we are the sons and daughters of Neanderthal and modern human interbreeding. Extraordinary claims require extraordinary evidence. Pääbo's evidence is extraordinary in only one respect--it's extraordinarily shaky. All that can be said for sure is that Neanderthals and modern humans shared a common ancestor. Well. Duh!
     Of course, I could be very wrong. 
     At least I admit it.

 * [Often attributed to Voltaire, this phrase was in fact coined by Evelyn Beatrice Hall (1868 - after 1939), an English writer who wrote under the pseudonym Stephen G. Tallentyre.]

7 comments:

  1. Applaus!
    And actually, my research goes from the notion that Neandertals did distinctly *not* give meaning to place/space the way we do.
    Interestingly, it turns out that the peers that referee my journal submissions do not quite like the suggestion that Neandertals organized their space quite different from us, at the intrasite-level: they too much love their spatially structured camp site reconstructions (my own ideas are more closely in line with Jan Kolen's "CLS" idea: the construction of a small temporary personal space by sweeping materials away). That was one of the main obstacles I bumped into with my research so far.
    If you look up the paper I have in press in Quat. International (I know, I am baiting you now - it will probably result in a new scathing blog-post with 1000 reasons why I am wrong and hence personally inept) and my 2001 paper in Archaeological Dialogues you'll also note that I have been suggesting a mobility pattern for Neandertals and their immediate predecessors (i.e. this concerns spatial behaviour and organisation on the landscape scale), that is quite different from modern hunter-gatherers and tries to steer away from the traditional ethnographically-inspired assumption of an organisation around "home-bases" etc. (I do not believe there is evidence for Middle Palaeolithic "home bases"). In that aspect too Neandertal spatial conceptions were quite different from "us", I argue.
    So I wonder where the hell you get the notion from that I, and I quote: "already assume[s] that they gave meaning to their spaces in the same way that you or I do". You couldn't be more wrong in that assumption.
    One thing I'll give you. While I feel they were different, I do not buy into the idea that Neandertals were lumbering idiots, more ape than human. That is a biased view as too much archaeological evidence speaks against it. As I point out in my Quat. Int. paper, it is a view based on pre-Darwinian Scala Naturea thinking seriously at odds with modern evolutionary thinking.

    ReplyDelete
  2. By the way, good science is also getting your facts straight, and you have a few of your facts wrong in your essay above.
    The genetic study by Svante Pääbo's group (Green et al. 2010) for example included more than four genomes and not only your one San from southern Africa but also Yoruba from West Africa.

    ReplyDelete
    Replies
    1. Hi,
      I have attempted to clarify what I think are some misunderstandings raised in Dr. Langbroek's comments, above. So I've composed a rapprochement post. It wouldn't work in one of these comment windows. Please go to http://thesubversivearchaeologist.blogspot.com/p/dear-dr.html and see what you think. I'm hoping that it puts things in perspective.

      Delete
  3. John Hawks has over the past weeks posted new analytical results of Neandertal-modern genetics twice, whereby he significantly increases the number of genomes involved (to over 1000 genomes included).

    part I: http://johnhawks.net/weblog/reviews/neandertals/pigmentation/neandertal-introgression-1000-genomes-style-2011.html

    part II: http://johnhawks.net/weblog/reviews/neandertals/neandertal_dna/1000-genomes-introgression-among-populations-2012.html

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