genetic linguistics
an approach to linguistics in which languages are classified according to their historical “family” relationships. The world’s 4,000 or so languages are conventionally divided into some 18 families, each of which is presumed to have developed from a common ancestral protolanguage. The larger families, such as Indo-European, are further divided into subfamilies, such as Celtic, Germanic, Aryan, and so on. See comparative linguistics; diachronic linguistics.