Language and culture expansion is explained by two main alternative diffusion models: demic diffusion, which involves mass movement of people; and cultural diffusion, which refers to cultural impact between populations, and involves limited genetic exchange between them. Language transfer since ancient times seems to be associated with an expansion of people[Mikhailova 2015], which is demonstrated, in most cases, by a significant replacement of patrilineal Y-DNA. Investigation of Y-DNA haplogroups help demonstrate e.g. the expansion of Han people in Northern and Southern China[Wen et al. 2004][Zhao et al. 2015], and the expansion of Arabs in the Arab peninsula[Chiaroni et al. 2010], and into Southern Levant and North Africa[Nebel et al. 2002]. Recently, the genetic history of Europe – including the expansion of hunter-gatherers and farmers – has been more precisely shaped thanks to ancient DNA research[Fu et al. 2016].
The recent expansion into Europe and Asia of Eurasian pastoralists, commonly identified with Indo-European speakers in mainstream diffusion models[Gimbutas 1993][Mallory 2014], was linked to haplogroup R1a[Semino 2000][Wells et al. 2001][Zerjal et al. 1999] due to the correlation of its modern geographic distribution with the ancient Corded Ware culture, and modern Balto-Slavic, Germanic, and Indo-Iranian speaking areas[Mirabal et al. 2009][Underhill et al. 2010].
Haplogroup R1b, which shows a modern Western European distribution peaking in the British Isles and around historically Basque-speaking regions[Myres et al. 2011][Lucotte 2015], was until recently associated with a Palaeolithic Western European origin[Morelli et al. 2010][Semino 2000]. With decreased age estimates of haplogroup R1b in Europe, a more recent spread with farming has been suggested[Myres et al. 2011][Chiaroni, Underhill, and Cavalli-Sforza 2009][Cruciani et al. 2011][Balaresque et al. 2010].
Following these genetic frameworks, Indo-European languages would have spread with an Indo-European-speaking, R1a-dominated, invasive, Eastern (Corded Ware culture) population into a non-Indo-European-speaking, R1b-dominated, Western Atlantic (Bell Beaker culture) population. This connection was the weakest link between the supposed archaeological and the attested historical European linguistic landscapes, needing explanatory models that included some kind of cultural diffusion model – e.g. technologically- or economically-based[Brandt et al. 2015].
Ancient DNA (aDNA) investigation allows us to disentangle complex human history[Slatkin and Racimo 2016]. The most recent research of ancient genetics[Haak et al. 2015][Allentoft et al. 2015][Mathieson et al. 2015], concerned with general population movements of Eurasians westwards from the steppe, has shown with their published data that haplogroup R1b was almost absent from Western Europe until after the expansion of Eurasian pastoralists, that the origin of most of its modern descendants in Western Europe is probably to be traced to the Pontic-Caspian steppes, and therefore that its expansion into central Europe happened at nearly the same time as haplogroup R1a, i.e. from the East and after ca. 3000 BC[Haak et al. 2015]. In these studies, R1a was almost absent from samples of the Yamna horizon, most of which belonged to haplogroup R1b-M269.
The earliest linguistic link between haplogroups R1b and R1a, deemed until recently a cultural diffusion along the Corded Ware – Bell Beaker contact area (and later among Bell Beaker groups), seems thus to be contested by the latest genetic research. However, alternative explanations are being sought to adapt older paradigms to the newest research, suggesting a direct connection of the expansion of Indo-European languages to the Corded Ware culture[Allentoft et al. 2015], and thus R1a as the genetic marker of the expansion of Proto-Indo-European speakers in Europe[Horvath 2015].
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