[danans]

It's not about the origin of a single language.

It's about the origin of a population whose widely dispersed descendants often speak a language whose primary features descend from the language spoken by the original population (albeit changed via thousands of years of drift and borrowing from other languages).

That doesn't mean that a) all features of the descendant language come from the origin language or b) all speakers of the descendant language have ancestry from the original population.