The key part of the story (which, frankly, I can’t recall whether I read in the NG version, or some other version)… is that the only trace of the prior species was in the mitochondria!
The mitochondrial genes of the California variety can be found nowhere else on earth. So when the the descendants of the common ancestors returned, over time all the males got run out of town… and the females successfully bore chicks under the new hegemony!
Something vaguely similar can be found in the anthropology literature, as I recall, but I do not remember whether the story (if true) was located in South America, Africa or Asia.
It is said that a fierce tribe had made a thorough conquest of another tribe in the region. All the males had either died protecting their women… or themselves, or ran away to fight another day - - but only if they were going to fight some other tribe easier to defeat.
The women were sorted out, under various protocols one might imagine … some liking their new companion, and others not so much.
But the twist in the story is that the females maintained their original language, in addition to mastering the language of their captors.
As they raised their children, generation after generation, the little boys and girls would know some of the mother’s language, while learning the father’s language too (of course). But at a certain age, the mothers would stop speaking their maternal language to the boys. And the boys would soon forget what they had ever known - - though there could very well be some sort of illicit use of the female language in the back rooms occupied by naughty boys, with smirks and laughs known of naughty boys everywhere in the world!
The daughters would grow up learning their mother’s language, communicated only between other females.
I love the story… I hope it is a true one!