There are two basic theories about the origin of language. The first, monogenesis, holds that language began only once. Groups speaking the original “proto-World” language became separated as primitive humans migrated into new territories. The tendency for pronunciations to change and for new words to appear among the isolated groups eventually made their speech unintelligible to one another. The second theory, multigenesis, finds that the incredible variety among modern languages, of which about 3,500 are still spoken, indicates that language was invented more than once. Both theories recognize that languages constantly change and that modern languages belong to a small number of language families, many of which have left written records from ancient times. These form the literature of regions and nations in the broadest sense—any information recorded in the form of carved, inked, engraved, chiseled, or molded letters or characters: deeds and wills, genealogies, administrative accounts and censuses, laws, the tenets and traditions of religions, manuals, histories, songs, and stories.
Whatever their ultimate origin, ancient languages either died out entirely or mutated into one or more modern languages. The group of languages descended from a single forebear constitutes a language family. Linguists generally agree that twenty-nine families exist, along with a few language isolates, such as Basque, whose affiliation is unclear: Afro-Asiatic, Algonquian, Altaic, Andean-Equatorial, Australian Aboriginal, Austro-Asiatic, Austronesian, Aztec-Tanoan, Caucasian, Dravidian, Eskimo-Aleut, Ge-Pano-Carib, Hokan, Indo-European, Indo-Pacific, Japanese, Khoisan, Korean, Macro-Chibchan, Macro-Siouan, Na-Dené, Niger-Congo, Nilo-Saharan, Oto-Manguean, Paleosiberian, Penutian, Sino-Tibetan, Tai, and Uralic. Some scholars distinguish even larger groupings—superfamilies, or macrophyla: Nostratic (including Afro-Asiatic, Dravidian, Indo-European, Altaic, Uralic, Korean), Dené-Caucasian (including Na-Dené, Sino-Tibetan, Eskimo-Aleut, Caucasian), Amerind (most native American Indian languages), and Austric (including Austronesian, Tai, Austro-Asiatic).
In most cases, the original parent language speakers remained more or less in their ancestral lands; most languages and literatures were regional. However, Indo-European and Sino-Tibetan peoples traveled and conquered so extensively that a few ancestor languages, particularly Latin, Greek, and Chinese, became international languages of commerce and learning.