August 14, 2023

Neat aDNA stories

The number of new palaeogenomics papers (whether human aDNA, environmental DNA, animal work, deep genetic tracing of hominin origins etc etc etc) can be pretty overwhelming. I was joking with a friend just recently that it would be really helpful if all of our aDNA colleagues would take a 6-month break from publishing to give us mere mortals a chance to catch up. Having said that, I'm glad they didn't immediately take me up on it, because July finally saw the publication of a much awaited prehistoric aDNA case study.¹

The site of Gurgy "Les Noisats" (Paris Basin, France) is a large flat cemetery dating to the early fifth millennium BC (the local Middle Neolithic) and more or less contemporary with the well known Cerny monuments. Lead author Maïté Rivollat and colleagues analysed the DNA of 110 of the 128 individuals excavated (the other 18 were too poorly preserved), undertook isotopic analysis of their teeth (and occasionally other bones) for information on diet and mobility, and compared all of this quite carefully to the excellent excavation data with pretty spectacular results.

The headline finding is that they identified a genetic genealogy spanning seven generations (as well as smaller five generation tree) with interesting implications for social structure and mobility. The adults buried in the cemetery are mostly male (the children are evenly split), and it looks from the genetics as if the mothers were not only (mostly) unrelated to the main patrilines, but only rarely related to each other.

The Gurgy genetic pedigrees showing more distant relations determined from IBD analysis (Rivollat et al. 2023, Fig 2)

Based on the Sr data, the authors suggest the community moved around within a fixed territory, perhaps every few decades (the incoming mothers all show Sr data consistent with the local area which is, admittedly, quite geologically diverse.

I'm quite taken by the age distribution and I think I'm going to spend quite a lot of time with the supplementary information thinking about it. In short, the oldest generation present includes a secondary burial of an adult male who was moved to Gurgy and appears to have been a focus for at least some of his descendants' graves. As the authors note, the first few generations to be buried at Gurgy comprise mostly adults while the final few represent mostly children. They interpret this as perhaps (and I'm grateful for their repeated qualifications) reflecting the Gurgy community coming into the local area, burying an important relative taken with them (having left their own dead children behind in another cemetery somewhere), then burying locally for a few generations before moving to new territory (leaving the dead children of the last generations behind at Gurgy).

In the spirit of thinking about kinship, I wonder if a slightly different scenario is also plausible. After about four generations, I would assume that the living community no longer has personal connections to the founder generation (that adult male secondary burial and his small cohort). Assman (and various colleagues across several decades of writing) term the embodied, everyday knowledge and experience of the recent past and its people "communicative memory", a form of uncontrolled knowledge with a ca 80-100 year (3-4 generation) span.² Here at Gurgy, after those four-ish generations (i.e., just beyond the scope of communicative memory of the founding ancestral burials), returning to this specific burial ground within a larger home area may not have seemed so pressing. I can imagine those adults from later generations exhuming their own honoured father/uncle/parent and starting a new cemetery elsewhere for their generation and the ones to follow.

I am thinking here particularly of the recent re-evaluations of early 2nd millennium British single graves by Bruck and Booth.³ Based on histological and radiocarbon data, they suggest that a number of these graves represent individuals who were interred anywhere from decades to a century after they died, in other words that they remained in circulation (perhaps socially alive) for a few generations. Then, they seem to have passed out of living memory, making their social death and interment possible and desirable.

The point I'm trying to make here is that the foundation and abandonment of these cemeteries may well have been cyclical and not related to migratory events (or perhaps only with the normal generational mobilities practiced in some places and times, such as Middle Neolithic (5th millennium BC) central France). The three to four generation lifespan may indicate instead the period of time for a known and loved family or community member and their generational cohort to fade from living memory into a more vaguely known ancestor, and thus become a less imperative focus for living ritual practices, such as funerary rites.