Cultural differences, including language, may be a possible driver of biological evolution, research implies. An article in Discover Magazine reports on research involving the Xavánte, an Amazon aboriginal tribe, and concludes:
Hostile neighbors still tend to exchange genes (e.g., kidnapping of women for brides, or slaves which are eventually assimilated into the enslaving tribe). Only a small amount of gene flow is necessary to prevent the accumulation of group-level differences. So you need strong between group selection to maintain those differences. In contrast, cultural differences can easily manifest in large between group variation, and little within group variation. An accent is the most obvious illustration. A tribe can easily have a distinctive accent which immediately separates it from its neighbors, and only manifests modest within group variation (e.g., along generational lines). The model posited here is that these between group cultural differences are powerful enough to driven biological differences. Are they? I am not sure that they are at this fine a scale, but am open to the proposition.