information:classification, structural:summarization
Contact languages

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, even if this family's relation to other families is not known.

Language contact can lead to the development of new languages from the mixture of two or more languages for the purposes of interactions between two groups who speak different languages. Languages that arise in order for two groups to communicate with each other to engage in commercial trade or that appeared as a result of colonialism are called pidgin. Pidgins are an example of linguistic and cultural expansion caused by language contact. However, language contact can also lead to cultural divisions. In some cases, two different language speaking groups can feel territorial towards their language and do not want any changes to be made to it. This causes language boundaries and groups in contact are not willing to make any compromises to accommodate the other language.