On Nov 16, 2023, at 12:00 PM, Iain via groups.io <gubbins@...> wrote:

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Hi Ed,

I don't know that there's been a lot of talk specifically about Colmar 239, but if you're basing your origin estimates off Globetrekker, then you're in for a bad time. Globetrekker effectively brings Family Tree DNA up-to-date with the efforts that Rob Spencer, Hunter Provyn and others have been doing for a few years now, but no-one really comes close to an accurate solution because the biases in the data still haven't been correctly accounted for, and the ancient DNA (in my opinion) hasn't been given the right weighting in the calculations.

The problem with assigning origins based on ancient DNA is the same as assigning origins based on modern testers: how much does one sample really tell you? The key here is contemporaneity. A sample like Ploti?tě nad Labem 1, who lived within a few generations of the R-U106 MRCA, says a lot about where R-U106 formed. Colmar 239, living 1000 years or so after the R-A10645 MRCA, says much less about where R-A10645 formed. We also have to be careful with our nomenclature: an ancient DNA sample may not be tested for all the SNPs in a haplogroup, therefore may descend from an intermediate haplogroup that is now either untested or extinct; similarly the sample may be positive for downstream sub-clades, for either not positive for all SNPs, or not tested for any.

If we assume a front speed of a between one and a few km/year for human migrations (https://www.pnas.org/doi/10.1073/pnas.1920051117), we can presume that R-U106 was founded within a few hundred km of where Ploti?tě nad Labem 1 was buried. This puts the origin of R-U106 in the vicinity of Bohemia, although doesn't allow us to definitively narrow it down to a specific country. If we do the same to Colmar 239, we can say that R-A10645 was founded somewhere within between one and a few thousand km of the La Tene culture, i.e., somewhere within Europe. That's not very constraining.

In both cases, we can say that at least some of R-U106 passed through the Bohemian part of the Corded Ware Culture, and that some of R-A10645 passed through the La Tene culture. In all likelihood, proportionally more of R-U106 probably passed through the Bohemian CWC because there had been much less time for R-U106 to diverge into different regions and cultures by that point. So, not only is Ploti?tě nad Labem 1 more constraining geographically regarding the origin of R-U106 than Colmar 239 is of R-A10645, but it also says more specifically about what cultures our contemporary early R-U106 ancestors were doing at the time. By contrast, by 600 BC, R-A10645 could have been spread to many different cultures in many different places, and we only sample one.

To put some numbers on this, imagine a population that diffuses out at a constant rate over time. It might cover 1000 square km after 100 years, 4000 square km after 200 years, 9000 square km after 300 years, and 2.5 million square km (1/4 of Europe) after 5000 years, etc. Imagine a tester in a 5000-year-old haplogroup like R-U106 today. We can draw a circle around him of 2.5 million square km and say that there's a 68% chance that the origin of R-U106 lies within that circle. If we have ancient DNA that's from 1000 years after R-U106 split, then we can draw a circle of 100,000 square km around the burial, thus that ancient DNA is 25 times more precise, and thus "worth" 25 modern testers today. For Ploti?tě nad Labem 1, we are dealing with a sample probably about 100 years or so after R-U106 split, thus the circle is 2500 times smaller, and that ancient DNA is "worth" 2500 modern testers in terms of defining origins.

Of course, populations move and spread and haven't expanded at a constant size, and all sorts of other confounding factors so, actually, each ancient DNA sample is "worth" much more than this, because it strips out all of these systematic trends. But the comparative "worth" of Ploti?tě nad Labem 1 is still more than 100 times that of Colmar 239 by this argument, and Colmar 239 on its own probably doesn't say much more about the origins of R-A10645 than the existing 42 FTDNA testers already did.

The take-home point here, then, is that ancient DNA needs to assigned to a contemporary haplogroup (not a much more ancient one) before it says anything about our ancestors, and it is only samples really close to the TMRCA of the haplogroup that can be so incredibly defining in terms of origins.

Cheers,

Iain.