The concept is due to Harold C. Fleming (1987), who proposed such a "mega-super-phylum" for the languages of Eurasia, termed Borean or Boreal in Fleming (1991) and later publications. In Fleming's model, Borean includes ten different groups: Afrasian (his term for Afroasiatic), Kartvelian, Dravidian, a group comprising Sumerian, Elamitic, and some other extinct languages of the ancient Near East, Eurasiatic (a proposal of Joseph Greenberg that includes Indo-European, Uralic, Altaic, and several other language families), Macro-Caucasian (a proposal of John Bengtson that includes Basque and Burushaski), Yeniseian, Sino-Tibetan, Na-Dene, and Amerind.
Fleming writes that his work on Borean is inspired by Greenberg's exploration of Eurasiatic, and is oriented towards the concept of "valid taxon". He rejects Nostratic, a proposed macrofamily somewhat broader than Eurasiatic, and withholds judgment on Dené–Caucasian, a proposal that would encompass Sino-Tibetan, Yeniseian, Basque, and several other language families and isolates. Fleming calls Borean a "phyletic chain" rather than a super-phylum. He notes that his model of Borean is similar to Morris Swadesh's Vasco-Dene proposal, although he also sees similarities between Vasco-Dene and Dené–Caucasian. He sees Borean as closely associated with the appearance of the Upper Paleolithic in the Levant, Europe, and western Eurasia from 50 thousand to 45 thousand years ago, and observes that it is primarily associated with human populations of Caucasoid and Northern Mongoloid physical appearance, the exceptions being southern India, southern China, southwestern Ethiopia, northern Nigeria, and the Chad Republic.
As envisaged by Sergei Starostin (2002), Borean is divided into two groups, Nostratic and Dene–Daic, the latter consisting of the Dené–Caucasian and Austric macrofamilies. Starostin tentatively dates the Borean proto-language to the Upper Paleolithic, approximately 16 thousand years ago. Starostin's model of Borean would thus include most languages of Eurasia, as well as the Afroasiatic languages of North Africa and the Horn of Africa, and the Eskimo–Aleut and the Na-Dene languages of the New World.
Murray Gell-Mann, Ilia Peiros, and Georgiy Starostin maintain that the comparative method has provided strong evidence for some linguistic superfamilies (Sino-Caucasian and Eurasiatic), but not so far for others (Afroasiatic and Austric). Their view is that since some of these families have not yet been reconstructed and others still require improvement, it is impossible to apply the strict comparative method to even older and larger groups. However, they consider this only a technical rather than a theoretical problem, and reject the idea that linguistic relationships further back in time than 10 thousand years before the present cannot be reconstructed, since the "main objects of research in this case are not modern languages, but reconstructed proto-languages which turn out to be more similar to one another than their modern day descendants." They believe that good reconstructions of superfamilies such as Eurasiatic will eventually help in investigating still deeper linguistic relationships. While such 'ultra-deep' relationships can currently be discussed only on a speculative level, they maintain that the numerous morphemic similarities between language families of Eurasia, many of which Sergei Starostin compiled into a special database that he later supplemented by his own findings, are unlikely to be due to chance, making it possible to formulate a Borean super-superfamily hypothesis.
They have also suggested possible links between 'Borean' and other families. In their view comparisons with 'Borean' data suggest that Khoisan cannot be included within it but that more distant connections on an even deeper level might be possible, that how the African superfamilies Niger–Congo, East Sudanic, Central Sudanic and Kordofanian are related to Borean remains to be investigated, that the situation with the native languages of the Americas remains unresolved, and that while there are some lexical similarities between Borean and the Trans–New Guinea languages, these remain too scarce to establish a firm connection. They comment that while preliminary data indicates possible connections between Borean and some superfamilies from Africa, the Americas, and the Indo-Pacific region further research is needed to determine whether these additional superfamilies are related to Borean or unidentified branches of it. Gell-Mann et al. note that their proposed model of Borean differs significantly from that of Fleming.