I want to draw your attention to several key points on Jan Apel's diagram.
|Dates are B.C.|
First, you'll notice that the continuity of pressure flaking is owed mostly to Northeast Asia and probably comes from the Altai region (5900 B.C.) where the technique may have roots back to the Upper Paleolithic and spread from there to the Americas. (However it is absent at Malta-Buret.)
The technique was also used in the West since Late Paleolithic but seems to have died out almost everywhere.
Although not shown, bifacial surface pressure flaking is probable in Mezraa-Teleilat (Southeast Anatolia) (Coskunsu, 2002) around the Pottery Neolithic (PN). It's possible that the R1 paragroup, ceramic technology and pressure flaking technology came as a package from Central Asia towards the end of the PPNB in the Northern Middle East.
Second, you'll notice that the emergence of bifacial surface pressure flaking in the North Black Sea region roughly coincides with the emergence of the North Pontic pastoral cultures and copper technology. This concave base also spreads from the Pontic to Afansevo in the East and with the later Single Grave tradition to the West.
Arrowheads don't equal haplogroups, but sudden changes in lithic technology should alert us to possible male population movements. I would suggest that changes in the North Pontic is a result of a male migration from the NE Middle East/Northern Zargos.
Thirdly, pressure flaking re-emerges in the Iberian peninsula at the end of the fourth millennium. Although this is 300-400 years before the earliest Beaker dates in the Tagus Estuary, the technology leaves Iberia with the Beakers.
There's two or more possibilities what may have been going on in the late pre-Beaker 4th millenium.
One is slow process where Saharan pastolists were slowly gaining a foothold in certain regions of Iberia. I doubt Iberia was invaded on a Tuesday night, 2783. Immigration could have lasted centuries and proper "International Beaker" probably didn't exist yet. It couldn't have since it acquired so many Iberian traits and that didn't happen instantly.
One early Chalcolithic example may be the very respectable frequency of L3F in Late Neolithic SE Iberia reflecting intrusion from the Southern Sahel. L3F has been linked, along with R1b-V88 with the spread of Chadic languages in Africa and is otherwise absent earlier in the European Neolithic. If L3F women migrated to SE Iberia, they certainly came with L3F men, who might very well have R1b-V88 (and others) and who would have been pressure flakers on barbed projectiles.
Another possibility is that the culture of Almeria was more directly influenced by trade and movements from the Northern Middle East. There does seem to be cultural communication between the two. As for L3F, I'll link to a recent paper in another post.