Dear Harald #2

The ancIBD method paper from the David Reich Lab was just published in Nature (open access here). It's a very useful effort, but the authors are still somewhat confused about the origin of the Corded Ware culture (CWC) population. From the paper (emphasis is mine):

This direct evidence that most Corded Ware ancestry must have genealogical links to people associated with Yamnaya culture spanning on the order of at most a few hundred years is inconsistent with the hypothesis that the Steppe-like ancestry in the Corded Ware primarily reflects an origin in as-of-now unsampled cultures genetically similar to the Yamnaya but related to them only a millennium earlier.

This is basically a straw man argument, because it's easy to debunk. So why put it in the paper? Well, as far as I can see, to make the idea that the CWC is derived from Yamnaya look more plausible.

This idea, that the CWC is an offshoot of Yamnaya, seems to be the favorite explanation for the appearance of the CWC among the scientists at the David Reich Lab.

However, I'd say they're facing a major problem with that, because the CWC and Yamnaya populations have largely different paternal origins. That is, CWC males mostly belong to Y-haplogroups R1a-M417 and R1b-L51, while Yamnaya males almost exclusively belong to Y-haplogroup R1b-Z2103.

Indeed, as far as I know, there are no reliable instances of R1a-M417 or R1b-L51 in any published or yet to be published Yamnaya samples.

But it is possible to reconcile the Y-haplogroup data with the ancIBD results if we assume that the peoples associated with the Corded Ware, Yamnaya and also Afanasievo cultures expanded from a genetically more diverse ancestral gene pool, each taking a specific subset of the variation with them.

This gene pool would've existed somewhere in Eastern Europe, probably at the western end of the Pontic-Caspian steppe, at most a few hundred years before the appearance of the earliest CWC burials in what is now Poland.

Moreover, the split between the CWC and Yamnaya populations need not have been a clean one, with long-range contacts and largely female-mediated mixing maintained for generations, adding to the already close genealogical links between them.

Citation...

Ringbauer, H., Huang, Y., Akbari, A. et al. Accurate detection of identity-by-descent segments in human ancient DNA. Nat Genet (2023). https://doi.org/10.1038/s41588-023-01582-w

See also...

On the origin of the Corded Ware people

Dear Harald...

I've started analyzing the Identity-by-Descent (IBD) data from the recent Ringbauer et al. preprint (see here). Unfortunately, it'll take me a few weeks to do this properly, so I won't be able to write anything detailed on the topic for a while.

Meantime, this is the comment that I left for the authors at bioRxiv (at this time it's still being approved, but it should appear there within a day or so, possibly along with a reply from the authors):

Hello authors,

Thanks for the interesting preprint and data. However, I'd like to see you address a couple of technical issues and perhaps one theoretical issue in the final manuscript:

- the output you posted shows some unusual results, which are potentially false positives that appear to be concentrated among the shotgun and noUDG samples. I'm guessing that this is due to the same types of ancient DNA damage creating IBD-like patterns in these samples. If so, isn't there a risk that many or even most of the individuals in your analysis are affected by this problem to some degree, which might be skewing your estimates of genealogical relatedness between them?

- many individuals from groups that have experienced founder effects, such as Ashkenazi Jews, appear to be close genetic cousins, even though they're not genealogical cousins. Basically, the reason for this is reduced haplotype diversity in such populations. Have you considered the possibility that at least some of the close relationships that you're seeing between individuals and populations might be exaggerated by founder effects?

- thanks to ancient DNA we've learned that the Yamnaya phenomenon isn't just an archeological horizon, but also a closely related and genetically very similar group of people. Indeed, in my mind, ancient DNA has helped to redefine the Yamnaya concept, with Y-chromosome haplogroup R1b-Z2103 now being one of the key traits of the Yamnaya identity. So considering that the Corded Ware people are not rich in R1b-Z2103, and even the earliest Corded Ware individuals are somewhat different from the Yamnaya people in terms of genome-wide genetic structure, it doesn't seem right to keep claiming that the Corded Ware population is derived from Yamnaya. I can't see anything in your IBD data that would preclude the idea that the Corded Ware and Yamnaya peoples were different populations derived from the same as yet unsampled pre-Yamnaya/post-Sredny steppe group.

See also...

Dear Harald #2

On the origin of the Corded Ware people