You seem to be confusing culture with genetics and I assure you, the former is far more divisive then the latter. A pair of Irish parents can absolutely have an English child simply by having and raising that child in England. I know this because I went to school with several of them. And as for those "36.2 million Irishmen living in the USA." They're not Irish, they're Yanks with Irish ancestry, just like I'm an Englishman with Welsh, Swiss and we're pretty sure Norman and Nordic ancestry (among a great many others.) Now when it comes to B5's telepaths, the separation between teep and mundane isn't at all genetic because the telepath gene is present in most if not all humans, it's just latent in most cases (that's why dust works.) The difference is entierly cultural. telepaths perceive the world around them in a fundamentally different way that mundanes cannot comprehend and by which they automatically feel threatened.