Dené–Caucasian is a proposed language family that includes widely-separated language groups spoken in the Northern Hemisphere: Sino-Tibetan languages, Yeniseian languages, Burushaski and North Caucasian languages in Asia; Na-Dené languages in North America; and the Vasconic languages from Europe (including Basque). A narrower connection specifically between North American Na-Dené and Siberian Yeniseian (the Dené–Yeniseian languages hypothesis) was proposed by Edward Vajda in 2008, and has met with some acceptance within the community of professional linguists. The validity of the rest of the family, however, is viewed as doubtful or rejected by nearly all historical linguists. History of the hypothesis 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. The inclusion of the Na-Dené languages has been somewhat complicated by the ongoing dispute over whether Haida belongs to the family. The proponents of the Dené–Caucasian hypothesis incline towards supporters of Haida's membership in Na-Dené, such as Heinz-Jürgen Pinnow or, most recently, John Enrico. Edward J. Vajda, who otherwise rejects the Dené–Caucasian hypothesis, has suggested that Tlingit, Eyak, and the Athabaskan