Language family
A language family is a group of languages related through descent from a common ancestral language or parental language, called the proto-language of that family. The term "family" reflects the tree model of language origination in historical linguistics, which makes use of a metaphor comparing languages to people in a biological family tree, or in a subsequent modification, to species in a phylogenetic tree of evolutionary taxonomy. Linguists therefore describe the daughter languages within a language family as being genetically related. The divergence of a proto-language into daughter languages typically occurs through geographical separation, with different regional dialects of the proto-language spoken by different speech communities undergoing different language changes and thus becoming distinct languages from each other.
One well-known example of a language family is the Romance languages, including Spanish, French, Italian, Portuguese, Romanian, and many others, all of which are descended from the spoken Latin of the ancient Roman Empire. The Romance family itself is part of the larger Indo-European family, which includes many other languages native to Europe and South Asia, such as English and Hindi, all believed to be descended from a common ancestor language Proto-Indo-European, spoken several thousand years ago.
The language families with the most speakers are the Indo-European family and the Sino-Tibetan family, the latter mainly due to the many speakers of Mandarin Chinese in China. A language family may contain any number of languages: some families, such as the Austronesian and Niger-Congo families, contain hundreds of different languages, while some languages, termed isolates, are not known to be related to any other languages and therefore constitute a family consisting of only one language.
Membership of languages in a language family is established by research in comparative linguistics. Genealogically related languages can be identified by their shared retentions; that is, they share systematic similarities that cannot be explained as due to chance, or to effects of language contact (such as borrowing or convergence), and therefore must be features inherited from their shared common ancestor. However, some sets of languages may in fact be derived from a common ancestor but have diverged enough from each other that their relationship is no longer detectable; and some languages have not been studied in enough detail to be classified, and therefore their family membership is unknown.