About Proto-Germanic

[Orentil]

"A long transition follows the arrival of Bell Beakers, from around 2200 BC to 1700–1600 BC, which continues in part Late Neolithic traditions—such as longhouses, flintwork, metalwork and burial rites—and incorporates them to the new culture (Figure 63). The Dagger Period integrated the diverse cultural traditions of the previous period into a single south Scandinavian cultural sphere under the influence of Bell Beakers (Prescott 2009), which suggests the formation of “a shared Nordic language based upon the frequent interaction that followed from the distribution of flint daggers” (Kristiansen 2009)."

Excellent summary, this is exactly what I meant. From all theories I know, this is the most convincing. And the Allentoft genetic results fit perfectly to the archaeological conclusions above about the dagger period.