The hypothesis of common origin for some or all of these languages—that is, the theory that they form a language family—was widespread before the 1960s, but has almost no supporters among specialists today. Opponents of the Altaic hypothesis maintain that the similarities are due to areal interaction between the language groups concerned. The inclusion of Korean and Japanese has also been criticized and disputed by other linguists. As for Turkic, Tungusic, and Mongolic, if they were related genetically, earlier forms would be closer than modern forms. This is true for all accepted linguistic families. However, an analysis of the earliest written records of Mongolic and Turkic languages shows fewer similarities rather than more, which suggests that they do not share a common ancestor but rather have become more similar through language contact and areal effects. Because of this, most modern linguists do not accept the Altaic family.
The idea that the Turkic, Mongolic, and Tungusic languages are closely related was allegedly first published in 1730 by Philip Johan von Strahlenberg, a Swedish officer who traveled in the eastern Russian Empire while a prisoner of war after the Great Northern War. However, as has been pointed out by Alexis Manaster Ramer and Paul Sidwell (1997), von Strahlenberg actually opposed the idea of a closer relationship among the languages that later became known as "Altaic". Von Strahlenberg's classification was the first attempt to classify a large number of languages, some of which are Altaic.
The term "Altaic", as applied to a language family, was introduced in 1844 by Matthias Castrén, a Finnish philologist who made contributions to the study of the Uralic languages. As originally formulated by Castrén, Altaic included not only Turkic, Mongolian, and Manchu-Tungus (=Tungusic), but also Finno-Ugric and Samoyed.
The original Altaic family came to be known as the Ural–Altaic. In the "Ural–Altaic" nomenclature, Finno-Ugric and Samoyedic are "Uralic", whereas Turkic, Mongolic, and Tungusic are "Altaic", as are Korean and Japanese if they are included at all.
For much of the 19th and the early 20th centuries, the theory of a common Ural–Altaic family was widespread, based on such shared features as vowel harmony and agglutination. However, while the Ural–Altaic hypothesis can still be found in encyclopedias, atlases, and similar general references, it has generally been abandoned by linguists. For instance, it was characterized by Sergei Starostin as "an idea now completely discarded".