I don't really get how the authors came up with their three models:
- the "Paleolithic" model assumes beginning of expansion at 21 kBP; as this was unsupported under any mutation rate, I won't bother with it further.
- the "Neolithic" models had expansion beginning at 10.5kBP, that is about 2k prior to the known earliest colonization of Europe from Anatolia, that occurred around 6,700 years BC.
- the "recent" model has the expansion starting at 3kBP, but already at 3kBP R1b1b2 makes its earliest appearance at Lichtenstein in Germany, and indeed 3kBP takes us to the Iron Age, a period extremely unlikely to have been one of major dispersals into Europe, dispersals that could not have gone unnoticed by the literate civilizations of the time.
Here is what the authors have to say:
Our results show that an expansion in Neolithic or Mesolithic times (350 generations ago or 10 ky) leads to a lower sum of squared errors than post-glacial re-expansion started 700 generations ago (21 ky ago), regardless of assuming a GMR or EMR model (Figure 2 and Table 2). Using GMRs, simulations of recent (100 generations ago) and rapid expansions from three distinct origins provided a better fit to the geographical distribution of microsatellite diversity than did models with expansion started 350 generations ago. Although models of recent origins using GMRs provided poorer fit than a model of Neolithic expansion using the EMR (Figure 2 and Table 2), the small observed difference makes them however difficult to discriminate (odd ratio = 1.7; Figure 3).So, basically the "evolutionary" rate stands its own against the "germline" rate assuming that the Neolithic expansion started 2,000 years before it did, and using the "germline" rate for an expansion at a much later time than anyone would believe.
Not directly related to the paper, I looked at the ongoing Dodecad v3 results to possibly correlate the spread of R-M269 to Western Europe with the autosomal evidence. It appears that the "West European" autosomal component shows a stronger relationship to the "West Asian" one than the "East European" one. This is consistent with an episode of gene flow into Europe from West Asia that affected Western more than Eastern Europe, which parallels the R-M269 distribution in Europe.
More interestingly, I had previously traced a peculiar "Dagestan component" in Europe that, counter-intuitively, seemed to be maximized in the Northwest. Looking at the recent Caucasus Y-chromosome paper, I notice the presence of R-M269 in the Lezgins of Dagestan (~29.6%), as well as the Abkhaz (12.1%). Looking at my Dodecad v3 results, I obtain a value of 24.3% of the "West European" component in the Lezgins, and a value of 15.7% in the Adygei, who are linguistically related to the Abkhaz. By contrast, other R1b-rich populations (namely Armenians and Turks) from West Asia show no substantial evidence of the "West European" component.
PLoS ONE 6(6): e21592. doi:10.1371/journal.pone.0021592
Wave-of-Advance Models of the Diffusion of the Y Chromosome Haplogroup R1b1b2 in Europe
Per Sjödin1, Olivier François
Whether or not the spread of agriculture in Europe was accompanied by movements of people is a long-standing question in archeology and anthropology, which has been frequently addressed with the help of population genetic data. Estimates on dates of expansion and geographic origins obtained from genetic data are however sensitive to the calibration of mutation rates and to the mathematical models used to perform inference. For instance, recent data on the Y chromosome haplogroup R1b1b2 (M269) have either suggested a Neolithic origin for European paternal lineages or a more ancient Paleolithic origin depending on the calibration of Y-STR mutation rates. Here we examine the date of expansion and the geographic origin of hgR1b1b2 considering two current estimates of mutation rates in a total of fourteen realistic wave-of-advance models. We report that a range expansion dating to the Paleolithic is unlikely to explain the observed geographical distribution of microsatellite diversity, and that whether the data is informative with respect to the spread of agriculture in Europe depends on the mutation rate assumption in a critical way.