The Neolithic dispersal in Europe was headed by G2a people with "local" partners (above all I2a1 which is found in Treilles, Els Trocs, Funnel, Starcevo...). The G2a reached Languedoc and Catalonia being yet a majority (Avellaner, Treilles).

With the new Y-DNA samples from the Chalcolithic it's possible to see that Megalithism changed proportions. We have 8 I2a2 (adding La Mina and Atapuerca), 2 G2a, 1 I2a1 and a C1a for such period (it's true that some enthusiasts try to assign some of such samples to the Bell Beakers, but the extreme lowest datation for such samples is 2346 BC, and BB appeared in the Basque Country around 2350, they just might wait for the promised BB paper).

So it seems that as the Cardial culture spread an Anatolian haplo, the Megalithism favoured a "local" haplo. Just wondering if Bell Beakers' R1b was not the same case.

Take it as an ironic theory just to compare with the L51 case: I2a2 is first recorded in Mesolithic Ukraine and there was a Yamnayan carrying such clade... so Megalithism was delivered from the steppes also, even if Iberian Chalcolithics are devoid of steppe admixture (no matter because almost all Urnfield samples were I2a2 and spoke Celtic).