We have two extremes to avoid here.
Genetics do increase the probability of a language being related, but obviously
you can't assume that genetics are going to intuitively carry one's
My mother is French and German, but I speak
Spanish better than both and she speaks only English. I'm mostly Irish on
dad's side, but neither of us speak Irish Gaelic, though one day I hope I can
get the gumption to learn that great language. Yet, there are genetic
commonalities between an Irish and an Indian or a Hausa-speaker and an
Hebrew-speaker, and these need to be understood to grasp the big picture of
genetic, cultural and linguistic development through the ages.