Linguistically, that is. According to this Linguist List report from Edward Vajda, Johanna Nichols, and James Kari:
A long-sought connection between Siberian and North American language families has been demonstrated by linguists from Washington and Alaska. Professor Edward Vajda of Western Washington University (Bellingham), a specialist on the Ket language isolate spoken by a shrinking number of elders living along the Yenisei River of central Siberia, combining ten years of library and field work on Ket and relying on the earlier work of Heinrich Werner on the now-extinct relatives of Ket, has clarified the dauntingly complex morphology and phonology of Ket and its Yeniseic congeners. At a symposium held Feb. 26-27 at the University of Alaska, Fairbanks and a panel to take place Feb. 29 at the Alaska Anthropological Association annual meeting in Anchorage, Vajda shows that the abstract forms of lexical and grammatical morphemes and the rules of composition of the Ket verb find systematic and numerous parallels in the Na-Dene protolanguage reconstructed to account for the modern Tlingit and Eyak languages and the Athabaskan language family (whose daughters include Gwich’in, Koyukon, Dena’ina and others of Alaska, Hupa of California, and Navajo of the U.S. Southwest). The comparison was made possible by recent advances in the analysis of Tlingit phonology and Tlingit-Athabaskan-Eyak presented at the same symposium by Prof. Jeff Leer of the University of Alaska, Fairbanks, and by earlier work by Prof. Michael Krauss of UAF on the now-extinct Eyak language and on comparative Athabaskan, and on Athabaskan lexicography and verb stem analysis by symposium organizer Prof. James Kari of UAF. Working independently, Vajda and the Alaska linguists have arrived at abstract stem shapes and ancestral wordforms too numerous and displaying too many idiosyncratic parallels to be explained by anything other than common descent. The comparison also shows conclusively that Haida, sometimes associated with Na-Dene, is not related.
The distance from the Yeniseian range to that the most distant Athabaskan languages is the greatest overland distance covered by any known language spread not using wheeled transport or sails. Archaeologist Prof. Ben Potter of UAF reviewed the postglacial prehistory of Beringia and speculated that the Na-Dene speakers may descend from some of the earliest colonizers of the Americas, who eventually created the successful and long-lived Northern Archaic tool tradition that dominated interior and northern Alaska almost until historical times.
Vajda’s work has been well vetted. In addition to Na-Dene specialists Krauss, Leer, and Kari, who have reacted favorably, the symposium was also attended by historical linguists Prof. Eric P. Hamp of the University of Chicago and Prof. Johanna Nichols of the University of California, Berkeley, both of whom announced their support for the proposed relationship, and Bernard Comrie, Director of the Linguistics Department, Max Planck Institute for Evolutionary Anthropology, Leipzig and professor at UC Santa Barbara, endorsed Vajda’s method.
As George Bryson says in his (remarkably thorough and accurate—kudos, Mr. Bryson!) Anchorage Daily News story, “Establishing that two such far-distant language groups are closely related is both demanding and rare in the exacting field of historical linguistics.” (Thanks for the links, Patrick!)