A new paper in Proceedings of the Royal Society dovetails with some posts I've put up on the peopling of Japan of late. The paper is Bayesian phylogenetic analysis supports an agricultural origin of Japonic languages:
Languages, like genes, evolve by a process of descent with modification. This striking similarity between biological and linguistic evolution allows us to apply phylogenetic methods to explore how languages, as well as the people who speak them, are related to one another through evolutionary history. Language phylogenies constructed with lexical data have so far revealed population expansions of Austronesian, Indo-European and Bantu speakers. However, how robustly a phylogenetic approach can chart the history of language evolution and what language phylogenies reveal about human prehistory must be investigated more thoroughly on a global scale. Here we report a phylogeny of 59 Japonic languages and dialects. We used this phylogeny to estimate time depth of its root and compared it with the time suggested by an agricultural expansion scenario for Japanese origin. In agreement with the scenario, our results indicate that Japonic languages descended from a common ancestor approximately 2182 years ago. Together with archaeological and biological evidence, our results suggest that the first farmers of Japan had a profound impact on the origins of both people and languages. On a broader level, our results are consistent with a theory that agricultural expansion is the principal factor for shaping global linguistic diversity.
I don't know the technical details of linguistics to comment, but the alignment between the linguistic model and archeology is pretty impressive to me. There's a 95% confidence interval which can push the time back to 4,000 years, so there's some fudge factor too. The basic technique is borrowed from phylogenetics. This is pretty clear when you notice that one of the algorithms seems to be the same one used in the rice genomics paper. Nick Wade covers the paper in The New York Times, so no need for me to give a blow-by-blow in a domain where I don't have much insight anyway. Dienekes Pontikos really likes these results and the method which they use. He, rightly in my opinion, believes that they lend more credence to the thesis promoted in the early 2000s using the same technique that the last common ancestor of Indo-European languages is very far back in time. I'm skeptical of this model, at least in its simple general form, but these results do push me into thinking that that model is more plausible. But to really understand this stuff I probably need to teach myself some rudimentary linguistics, so I guess we'll see. More broadly this gets to the question: did farming spread through demographic expansion or cultural diffusion? Obviously it's not an either/or. There's a small residual of Amerindian ancestry in American whites, so there was some diffusion through genetic assimilation. The Xhosa tribe of South Africa seem to have ~20% Khoisan ancestry. They're the group on the Bantu farming frontier, the last before the Bantu toolkit ceased to be effective and the Khoisan managed to maintain their hold before the whites arrived. Some of the admixture is from pastoralist Khoi, but some of it may also be from hunter-gatherer Bushmen. But here's my issue at this point: what are the examples where we know that hunter-gatherers picked up agriculture? The instances of Japan and the Bantu expansion are two where we're now rather sure that it was demographic expansion and replacement. Was it so different in the past? I think it may have been insofar as farming was less advanced a cultural toolkit in terms of its ability to overpower hunter-gatherers. And yet still I am becoming more convinced of the thesis of that farming spread through procreation, not propagation. My hesitation is mostly due to the reality that our understanding of the past is so clouded as a fundamental matter.