Wednesday 5 March 2014

Neanderthal Demise, V.2012: Dalén et al. Pimp Their Genomics. Thas Wha' I'm Talkin' Uhbout!*

No. Your senses aren't playing tricks on you. You're looking at a genuine, bona fide, blurt from The Subversive Archaeologist. For reals! I've been busying myself with other matters, including some serious homemaking (see Figure 1, at left).

Compared to geological time, my prolonged absence from the intertubes var. internets would be virtually imperceptible. So, as we're, all of us, good archaeologists, what's a nanoepoch among friends? [Inelegant segué warning!] Speaking of time, today's diatribe subject comment blurt should take little more than a nanomillenium of yours.

A tip o' the brown fedora to Iain Davidson for pointing me to this week's write-up, by Gail Glover, concerning a Molecular Biology and Evolution article from a couple of years ago (?). I noted it at the time, but evidently failed to consult that note thereafter! No worries! Still plenty of time before the door is closed on matters of human biological and cultural evolution. [Good news for those of us needing a little bit of job security!]

Dalén, L., L. Orlando, B. Shapiro, M. Brandström-Durling, R. Quam, M.T.P. Gilbert, J.C.D. Fernández-Lomana, E. Willerslev, J.L. Arsuaga, and A. Götherström. "Partial Genetic Turnover in Neandertals: Continuity in the East and Population Replacement in the West." Mol. Biol. Evol. 29(8):1893–1897, 2012. [doi:10.1093/molbev/mss074]
I risk ridicule even remarking on research of this kind, since my expertise doesn't encompass smaller organismic units than individuals and their behaviour. I'll say it: genomics is well beyond the limits of my mental acuity, beyond my purview, past my perspicacity, too complicated for my wee noggin. [It's been said that I have all the mental alacrity of a soap dish when it comes to Gs. Cs, Ts, and As.] [I should be flattered that someone has taken the time to get to know me!] However, forms of argument are well within my purview. Philosophically speaking, there are observations [data] and conclusions, and then there are the lines of reasoning that connect observations to conclusions. In other words, the observations become the evidence for conclusions by means of logical argument—otherwise known as interpretation. Consumers of research findings either have the wherewithal to be critical, or they are compelled, one way or another, to accept the findings of others by appeal to their authority—which is a logical fallacy—alternatively referred to as argumentum ab auctoritate (argument from authority). To whit, if Prof. So-and-So said it, it must be so. But, even the best minds can be wrong some times.
And, since argument from authority amounts to a claim for someone's infallibility, argument from authority is inherently flawed. After all, infallibility is humanly impossible! [Just ask me.] [On second thought. Don't.] And so, it is to argument that I will turn in this discussion, both the authors' and those of their consumers—i.e. those citing this research within the bigger picture of global human evolution. 

Dalén et al. (2012) examined mitochondrial DNA (mtDNA) from archaic bipedal apes across the geographic and temporal range of what are commonly referred to as "Classic" Neanderthals. Briefly, a Classic Neanderthal is identified using a suite of physical features that are outside the range of  contemporaries elsewhere in the world and today's humans. The cartoon below illustrates some of the salient distinguishing features.

The features that serve to distinguish Classic Neanderthals from people like you and me, and from just about every other bipedal ape that's ever trod on two feet. (Credit: hairymuseummatt (original photo), KaterBegemot (derivative work) [CC-BY-SA-2.0 (], via Wikimedia Commons. 

The authors observed that regardless of where in the Classic Neanderthal's range they took samples, those living prior to about 48,000 years ago [48 ka] shared more or less comparable degree of mtDNA heterogeneity. However, since about 48 ka those living in the west of that same range manifested a lesser degree of genetic variability that distinguished them from those further east, and from those that had lived in western Europe prior to 48 ka.

The authors conclude that some environmental or other process split the Classic Neanderthals into two reproductively isolated groups, and eventually saw the extinction of the original heterogeneous western genome. The following illustration is borrowed from Dalén et al. It shows the sampled locations and the cluster of western genotypes distinct from the one that spanned both the Classic Neanderthal's geographic and its temporal range.

Back to epistemology, specifically argument.

Palaeoanthropologists and archaeologists come in two basic flavours: those that cleave to the idea that western European Neanderthals were coeval with, and interbred with the modern humans that we know entered that region after about 48 ka. The other flavour of palaeo people holds the opposite view, that the Neanderthals and modern humans probably never met one another. I'm a representative of that second group. As a group, we seem to be in the minority.

Dalén et al.'s findings clearly support the school of thought to which I belong. Do I accept their findings prima facie? You bet I do! Am I relying on their authority? Yeppers! Am I therefore a damned fool? NOT necessarily. [Wait a second. What kind of a question is that? Who put you up to it? The nerve of some people!]

I'm not necessarily a damned fool. As you can see from the graphic depiction [above] of my intellectual position vis a vis Dalén et al., I'm on a precarious perch. As long as I stay put, I should be okay. But if I'm to live much longer I can't stay here forever. Do I march ahead and say "good on you, Dalén et al.," chancing an owie or two? Or, do I take the sensible course, and retrace my steps, metaphorically and physically declining to accept the authors' conclusions? Ahead, or back? Mine is the sort of situation they must have had in mind when they invented the phrase "on the horns of a dilemma." What if I side-stepped the issue? Meh. Not such a good tactic at this juncture. It'd hurt just as much as going forward, but with less intellectual and scholarly integrity.

Of course, I could try to delude myself into thinking that this was a fence, and that by sitting down right here, the worst that could happen is that some of my critics will think I'm wishy-washy. Nah! Not only am I replete with those two kinds of integrity [and a handful more, I might add], in my day job I'm very familiar with self-delusion. Like a good rationalization a self-delusion can be very calming at times. But, as a frequent reader of the Subversive Archaeologist, you'll be well aware of my natural inclination to take a position and argue it to death. Given the two alternatives, I think I'll stay where I am, waiting [perhaps in vain] for a deus ex machina to rescue me.

That's it then! Here I stay, sitting [well, standing] on the proverbial fence. I'll accept Dalén et al.'s conclusions PROVISIONALLY. That oughta satisfy the Argument Police AND the likes of you, Dear Reader. Hasta luego!

No comments:

Post a Comment

Thanks for visiting!

Note: only a member of this blog may post a comment.