As for the immigrant Indo-European and the presumably indigenous Dravidian languages in India, there is one major candidate genetic marker for immigration from the northwest. It is a Y-chromosome DNA type (J2a) rather than an mtDNA type, and its immigrant status is suggested by its presence at 10 to 20% frequency in high castes, both in Indo-European speakers and farthersouth among Dravidian speakers, and its near-absence in lower castes or “tribals” ( 8).
When dealing with language-genetic correlations, we must always be vigilant. In particular the following two points should always be remembered:
- Inference that a particular haplogroup existed in early speakers of a language does not mean that it was the only or even dominant haplogroup among them
- It does not mean that it was ever exclusive to the speakers of the language either
Finer-scale determination of the phylogeny, coupled with historical knowledge and direct typing of ancient DNA remains of historical peoples will surely help inform us more about the ancient origins of common Y-chromosome types.
The highlighted sentence from the abstract below agrees with my own thinking, since even if it is minimal (e.g., in the case of the East Eurasian components in Hungarians and Turks), I know of no case where a people has adopted a new language without even a trace of the patrilineages of the bearers of that language. This is quite useful, as it makes it possible that we may reconstruct some of the patrilineages of the proto-speakers of the language, e.g., in a manner similar to what I did for the case of Tocharian.
Science 9 September 2011:
Vol. 333 no. 6048 pp. 1390-1391
Mother Tongue and Y Chromosomes
Peter Forster, Colin Renfrew
Some 6000 different languages are spoken in the world today, and tracing the prehistory of languages and of language change by means of genetic markers has long been a goal (1). However, this has proven to be a more challenging task than simply tracing colonizations. Nevertheless, a number of genetic studies over the past few years have started to address language and language change before recorded history. A correlation is emerging that suggests language change in an already-populated region may require a minimum proportion of immigrant males, as reflected in Y-chromosome DNA types. By contrast, the female lineages, as indicated by mitochondrial DNA (mtDNA) types, do not reflect the survivor language but represent more ancient settlement.