Originally Posted by
Albion
I see. But I don't think J and G have much to do with Indo-European. IE probably developed in either the Pontic Steppe, Central Asia or Anatolia (unlikely). I don't think J2 and G are so associated with it.
G is prominent in Caucasians and Iranian peoples but quite rare amongst most IE's (Iranians excepted). J2 and G carriers must have been quite some elite to be able to replace the languages like that, I think it is unlikely.
More likely is that G2a spread to Europe during the Neolithic and some latter with the Indo-Europeans, Iranian nomads and the Alans on their way to Iberia.
It is important to note that these haplogroups are both found in areas which retained non-IE languages the longest (Etruscans in Italy, Rhaetians in the Alps, etc...)
I see them as Neolithic survivals, it is likely that much of Neolithic Europe was a mixture of G2a and I1 / 2 IMO.