Several factors are speculative. There is some (necessarily scant) evidence that Neolithic Central Europeans did not have the LPT gene but we know nothing of Atlantic Neolithics, among whom this trait is most common nowadays. This is important, I’d say, because the trait shows significant correlation with neutral genes, like Rh, what makes me think it was actually present in relative high levels among pre-Neolithic Europeans (why? accident maybe – otherwise I’d have to start speculating again about Magdalenian horse domestication).

Whatever the case the authors seem to have confirmed some selection in NW Europe for this trait (but looks neutral in the rest).