[4] Much of the early evidence adduced has been typological; in particular, both families have a complex agglutinative prefixing verb structure, which differs from most of the other languages in Asia and—to a lesser extent—North America.

The first peer-reviewed publication to propose the existence of a distinct Dene–Yeniseian family was written by the macrofamily supporter Merritt Ruhlen (1998) in Proceedings of the National Academy of Sciences, United States.

[7] As alluded to by Fortescue's comment, scientific investigations of long-range language family relationships have been complicated by an ideological dispute between the so-called "lumpers" and "splitters", with "lumpers" caricatured as bumbling amateurs willing to group together disparate, unrelated families based on chance resemblances[8] and the "splitters" caricatured as rigid enforcers of orthodoxy willing to "shout down" researchers who disagree with their belief that long-range connections are impossible to establish.

[9] At a symposium in Alaska in 2008, Edward Vajda of Western Washington University summarized ten years of research, based on verbal morphology and reconstructions of the proto-languages, indicating that the Yeniseian and Na-Dene families might be related.

Accompanying Vajda's lead paper are primary data on Na-Dene historical phonology by Jeff Leer, along with critiques by several linguistic specialists and articles on a range of topics (archaeology, prehistory, ethnogeography, genetics, kinship, and folklore) by experts in these fields.

He suggested that Yeniseian tone differences originated in the presence or absence of glottalized consonants in the syllable coda, as still present in the Na-Dene languages.

[10][11] As for the wider Dene–Caucasian hypothesis (see below), while Vajda did not find the kinds of morphological correspondences with these other families that he did with Yeniseian and Na-Dene, he did not rule out the possibility that such evidence exists, and urges that more work be done.

His conclusion was that, contrary to prevailing belief, such structures are often preserved intact with little change over several thousands of years, and as a result may actually be stronger evidence of a genetic connection than the lexical relationships that are traditionally sought.

As a result, he agreed with the consensus belief that lexical evidence of a genetic relationship becomes virtually undetectable after about 8,000 to 10,000 years of linguistic separation, but suggested that certain sorts of complex morphology may remain stable beyond this time period.

Vajda presents comparanda for an ancient Dene-Yeniseian possessive connector prefix (possibly *ŋ) that appears in idiosyncratic ways in Dene (or Athabaskan), Eyak, Tlingit, and Yeniseian nouns, postpositions, directionals, and demonstratives.

In his 2012 presentation, Vajda also addressed non-linguistic evidence, including analyses of Y-chromosome and mitochondrial DNA haplogroups, which are passed unchanged down the male and female lines, respectively, except for mutations.

[15][16] One significant exception is the critical review of the volume of collected papers by Lyle Campbell[17] and a response by Vajda[18] published in late 2011 that imply that the proposal is not settled at the present time.

Nonetheless, Starostin concedes that Vajda's work "is, by all means, a step forward", and that it "may eventually point the way towards research on grammaticalization paths in Yeniseian and Na-Dené".

[26] In addition, Wilson (2023) has argued that a cluster of related technology words in proto-Athabaskan and Yeniseian languages suggests a linguistic continuum between the two continents that extended well into the Common Era, clouding any conclusive evidence for the back-migration model.

In 1925, a supporting article summarizing his thoughts, albeit not written by him, entitled "The Similarities of Chinese and Indian Languages", was published in Science Supplements.

[41] A 2023 analysis by David Bradley using the standard techniques of comparative linguistics supports a distant genetic link between the Sino-Tibetan, Na-Dene, and Yeniseian language families.