Thanks, Herman (and Chris?), for this reference.
Both the study and the brief reactions so far confirm me in considering "genetics" only a parameter of secondary, derived importance depending on social inertia (which became stronger ca. 70 generations ago, i.e. ca. 350 CE, that is, around the date of the final redaction of what is now known as the generalized (sarvaparsada) Manava Dharma Sastra or Manu Smriti).
The real underlying parameter in the case of, for instance, the sufficiently attested spread of Vedic culture *within* the Indian subcontinent from 1700 BCE is to be understood in terms of memetics and memory culture.