Genetic classification One of the ways to classify human languages is according to their ancestry, i.e., their common origin. Languages which are genetically related have a common ancestor, i.e., they belong to a single language family, the structure of which is typically exhibited in a family tree. In historical linguistics, a language family is identified with a group of languages which all derive from a single common ancestor, that is, they all started off at some time in the past as no more than regional dialects of that ancestral language. The languages in a family are therefore linked in a genetic relationship. The number of language families currently spoken on the planet is around 300; further research will no doubt succeed in reducing this number by combining some families into larger families. As has already been said in one of the earlier classes, the branch of linguistics whose primary concern is the classification of languages is called comparative linguistics, which is divided into historical-comparative linguistics (concerned with genetic classification of languages) and typological-comparative linguistics (concerned with the classification of languages on the basis of presently existing common features). Thus a historical (genetic) classification of languages is established according to the degree to which they have a common genesis, and then analyses the processes of language evolution which led to this division of languages, attempting to present, at least in part, the causes of particular evolutionary processes.