Page "Language family" Paragraph 14

The concept of language families is based on the historical observation that languages develop dialects, which over time may diverge into distinct languages.

However, linguistic ancestry is less clear-cut than familiar biological ancestry, in which species do not crossbreed.

It is more like the evolution of microbes, with extensive lateral gene transfer: Quite distantly related languages may affect each other through language contact, which in extreme cases may lead to languages with no single ancestor, whether they be creoles or mixed languages.

In addition, a number of sign languages have developed in isolation and appear to have no relatives at all.

Nonetheless, such cases are relatively rare and most well-attested languages can be unambiguously classified as belonging to one language family or another.