Classifications similar to Dené–Caucasian were put forward in the 20th century by
Alfredo Trombetti,
Edward Sapir,
Robert Bleichsteiner,
Karl Bouda,
E. J. Furnée,
René Lafon, Robert Shafer,
Olivier Guy Tailleur,
Morris Swadesh,
Vladimir N. Toporov, and other scholars. Morris Swadesh included all of the members of Dené–Caucasian in a family that he called "Basque-Dennean" (when writing in English, 2006/1971: 223) or "
vascodene" (when writing in Spanish, 1959: 114). It was named for
Basque and
Navajo, the languages at its geographic extremes. According to Swadesh (1959: 114), it included "Basque, the Caucasian languages, Ural-Altaic, Dravidian, Tibeto-Burman, Chinese, Austronesian, Japanese, Chukchi (Siberia), Eskimo-Aleut, Wakash, and Na-Dene", and possibly "Sumerian". Swadesh's Basque-Dennean thus differed from Dené–Caucasian in including (1) Uralic, Altaic, Japanese, Chukotian, and Eskimo-Aleut (languages which are classed as
Eurasiatic by the followers of
Sergei Starostin and those of
Joseph Greenberg), (2)
Dravidian, which is classed as
Nostratic by Starostin's school, and (3)
Austronesian (which according to Starostin is indeed related to Dené–Caucasian, but only at the next stage up, which he termed Dené–Daic, and only via
Austric (see
Starostin's Borean macrofamily). Swadesh's colleague
Mary Haas attributes the origin of the Basque-Dennean hypothesis to
Edward Sapir. In the 1980s,
Sergei Starostin, using strict linguistic methods (proposing
regular phonological correspondences,
reconstructions,
glottochronology, etc.), became the first to put the idea that the Caucasian, Yeniseian and Sino-Tibetan languages are related on firmer ground. In 1991,
Sergei L. Nikolaev added the Na-Dené languages to Starostin's classification. In 1996,
John D. Bengtson added the
Vasconic languages (including Basque, its extinct relative or ancestor
Aquitanian, and possibly
Iberian), and in 1997 he proposed the inclusion of
Burushaski. The same year, in his article for
Mother Tongue, Bengtson concluded that
Sumerian might have been a remnant of a distinct subgroup of the Dené–Caucasian languages. In 1998,
Vitaly V. Shevoroshkin rejected the
Amerind affinity of the Almosan (
Algonquian-Wakashan) languages, suggesting instead that they had a relationship with Dené–Caucasian. Several years later, he offered a number of lexical and phonological correspondences between the North Caucasian,
Salishan, and
Wakashan languages, concluding that Salishan and Wakashan may represent a distinct branch of North Caucasian and that their separation from it must postdate the dissolution of the
Northeast Caucasian unity (Avar-Andi-Tsezian), which took place around the 2nd or 3rd millennium BC. ==Academic concerns with Dené–Caucasian==