Overturning assumptions: why genes matter in history

Martin had a comment below:

You equate language groups with ethnic, even political, groups. That's quite a stretch. Western archaeologists abandoned that idea in the 1970s.

I think I should expand a bit on my comment where I address Martin's assertion. I think I made it pretty clear that when it comes to burial styles or pottery motifs I render unto archaeologists their expertise, on the other hand, there's the old joke that archaeologists reduce the entirety of the past to material artifacts. Obviously such remains loom large because we unfortunately have no access to time travel machines and pottery is a robust & plentiful echo of the past (the data sets of pottery are large enough that you could do statistical analysis). That being said, in human historical genetics there has been a traditional focus on mtDNA for technical reasons (e.g., mtDNA is present in large quantities), but it is likely that this is distorting our picture of past genetic events. This is why when possible we need to draw upon as many sources of insight as possible to shed light upon the past.

As Martin implies by his comment archaeologists have to work with background assumptions. During the first half of the 20th century they were influenced by the racial ideas in common circulation in the West; naively coupling ethnicity, language, culture and inferring from the shift in material remains massive migrations. To some extent these extrapolations were nothing so much as epic fantasy fed by their own notions of national pride or racial destiny. After World War II archaeologists, and historical and human scientists in general, withdrew from this tendency, and leaned toward the other direction: peoples did not move, only culture did. Whereas previously historians and archaeologists might have posited that the Etrusans brought their civilization from distant shores, now they assumed that the society was a natural extension of indigenous traditions (with perhaps outside cultural influence). Similarly, they turned away from models where Anglo-Saxons drove Celts into the sea so as to affect ethnic change during the 6th century, and presumed that in fact the dynamic was one of elite emulation where the Germanic language and culture percolated from on high after the conquest by a small warrior elite.

These were assumptions, fed by some empirical data, but assumptions nonetheless. Skeletal analysis was not advanced enough (or feasible where cremation was dominant) to answer whether populations, or simply ideas, had moved. But assumptions need to be sensitive to new data and methods, and I don't think that many historical scientists have taken note of the power of genetic science in probing their axioms and changing the lay of the land. There are two clear examples of this. In regards to the multiple genetic data (from humans, living and dead , and cattle) that the Etruscans cluster in part with Anatolians as opposed to the rest of the Italian population, some archaeologists stated:

"The overwhelming proportion of archaeologists would regard the evidence for eastern origins of the Etruscans as negligible," said Anthony Tuck, an archaeologist at the University of Massachusetts Center for Etruscan Studies.

Historical science is interpretative, and those interpretations are embedded in systems of assumptions. We know now that a significant proportion of Etruscan ancestry was certainly exogenous and of recent vintage to the north-central regions of Italy. We also know that these populations were probably derived from Anatolia. They have left descendants in the local region of what was Etruria, and they have left genetic clues to their cultural impact via Anatolian cattle lineages extant in the region, and DNA retrieved from subfossils from putative Etruscan burials also suggests eastern Mediterranean associations. The question is not whether Etruscans were exogenous or indigenous, we know that they were in part at least outsiders genetically. The question is what aspect of their culture was derived from the indigenous societies, who they likely assimilated, and what was derived from Anatolia. Prior to the genetic data archaeologists constructed models which assumed that indigenous derivation was the overwhelming probability, and so I'm sure that colored their perception of the material remains. In earlier decades they likely would have assumed that there was an alien racial element and would have seen greater cultural discontinuities. The reality is not either/or, and it need not rest upon a priori presuppositions.

The second case study I want to focus on are the Anglo-Saxons and their relation to the British substrate of what has become England. Gildas' apocalyptic annals of the Saxon invasions of Britain, combined with chauvinistic prejudice against Celtic peoples, resulted in an early 20th century perception among the English that they were the descendants of Germans and not the Celts and Latinized-Celts who inhabited the land when the Romans left early in the 5th century. The Welsh & Irish were looked upon as alien & inferior races. The political context is also pretty well known, so this was very convenient. Similarly, after World War II the collegiality of German peoples, which had included the English, was no more. The winds had changed and a model which posited elite emulation was ascendant. There were always problems with this; unlike Gaul the natives did not manage to impose their language or religion on their barbarian overlords. To the contrary, English has always been severely deficient in any Celtic loan words (which reassured those who wanted to believe that the Celts were fundamentally different from the Germanic Anglo-Saxons). When I read Norman Davies' The Isles the author presented the consensus model of elite emulation and culture diffusion. He noted that this hypothesis was not all conjecture: there are historical documents from the early Anglo-Saxon period which allude to Celtic speaking (British) subjects of the new dispensation. The "blood price" for a Celt was, not surprisingly, lower than for that of a Saxon. This stipulation suggests that Celts were numerous enough that they had to be accounted for in the legal codes. Combined with the working assumption that culture, not people, tends to be more mobile and Davies' model was entirely plausible. I believed it.

But contemporaneously with Davies' work a new field was emerging which attempted to draw historical inferences from phylogenetic trees constructed from ancestrally informative genes. This field was enabled by technical improvements (e.g., PCR, better extraction techniques, cheaper computation), but once the details were ironed out a profusion of papers and popular books appeared on the scene which attempted to sketch out history via the relationships discernible from genetics. An early precursor of this line of thinking was presented in The History and Geography of Human Genes, L. L. Cavalli-Sforza's magnum opus. Cavalli-Sforza's post-doc, Spencer Wells, published Journey of Man, while Bryan Sykes, an Oxford geneticist with a penchant for marketing, came out with The Seven Daughters of Eve. The field was "hot," and there are many other books out there which use the insights from scientific genealogy to converge upon historical truths. But there's a problem here: a lot of sloppy scholarship has come out of this field. Scientists who look at a phylogenetic tree or allele frequencies make their inferences in a thin background of extra-genetic data. In other words, they don't know much history or archaeology. Reading books and papers within historical population genetics can be wince-inducing because of this deficiency, the peer review process obviously doesn't include any historians who are well versed in matters not phylogenetic.

If the past is a stool, it needs to be propped up on multiple legs lest it fall over (to borrow a metaphor from Mitt Romney). A synthetic discipline needs different actors to throw in their two cents. I am worried that too many geneticists think that historical detail is an afterthought, when the use of their tools toward the ends which they aim for are predicated upon the importance of historical detail! I also am a bit shocked sometimes at the ignorance of historical scholars of this whole new domain of knowledge which offers precise and systematic inferences for them to work with. So let's go back to the Anglo-Saxons. What do the genes tell us? A fair amount. In short, it seems that neither cultural diffusion nor replacement explains the total pattern of genetic variation within the present day expanse of England. It also seems that contrary to the early 20th century line of thinking on any given gene someone who is English is more likely to share a most recent common ancestor with the Irish or Welsh as opposed to a German. Nevertheless, in contradiction to the idea that peoples don't move, cultures do, it seems that a substantial (genetically non-trivial) proportion of the ancestry of the English derives from the Anglo-Saxons. That is, on a large minority of genes the English have a more recent comment ancestor with the Dutch and Germans, and not the other peoples of the British Isles. This varies as a function of geography; in East Anglia the Anglo-Saxon proportion may predominate. It also might vary as a function of sex; male lineages seem to show a stronger Anglo-Saxon stamp than female ones. This is intelligible when filtered through social science assumptions as to the nature of mating systems in the pre-modern world. East Anglia was the core of the "Saxon Shore" from which the barbarians expanded across the rest of England. Distant regions such as Cornwall are not surprisingly predominantly pre-Saxon in ancestry; not only was there a Celtic population in this region deep into historical times, but a wave of Anglo-Saxon advance would dilute the genetic signal of the Germans the further away you moved from the point of disembarkation. There are other small data points which are not surprising if you know some history; Scandinavian ancestry is significant within what was once the Danelaw. Differences between the Welsh and English are far crisper on the male lineages than female ones. This is comprehensible when you note the likelihood of male biased long distance migration from Germany, as well as normative patrilocality so that women would be moving to the village of their husband while men would remain where they were born. Gene flow across Offa's Dyke would then occur via female lineages as opposed to male ones.

The big takeaway picture is that we live in an age where assumptions are rooted in the possibility of a wide range of facts and methods. When one has little to go on one must make assumptions with little basis as a matter of course. We don't have that excuse anymore. Historically oriented scholars should read the genetic literature because it is accessible and copious. Geneticists should make the acquaintance of historians because quite often their knowledge of the past seems little more advanced than what you would find in an elementary school book.

Note: The provisionality of some of the genetic data needs to be kept in mind. Some of Spencer Wells' inferences based on M17/Ra1a seem unlikely now that the phylogenetic tree is being revised.