Grammar sharing does not occur only between pairs of languages

A. Not only do we see distinct languages with aspects of grammar that one must have borrowed from the other, but even distinct language groups or families that are so similar to one another in structure that it is clear that over time, a certain complex of grammatical traits has been shared and distributed widely, creating what is called a language area.

B. Thus, in a language area, although it can appear that all the languages trace back to a single ancestor, in fact, they may trace to several different proto-languages. Their similarity has arisen over time from grammar mixture.