within 5,000 to 9,000 years making the application of comparative methods to ancient superfamilies highly questionable. Additionally, apparent cognates can arise by chance or from loan words. Without the existence of statistical estimates of chance collisions, conclusions based on comparison alone are thus viewed as doubtful. Stefan Georg and Alexander Vovin, who, unlike many of their colleagues, do not stipulate a priori that attempts to find ancient relationships are bound to fail, examined Greenberg's claims in detail. They state that Greenberg's morphological arguments are the correct approach to determining families, but doubt his conclusions. They write "[Greenberg's] 72 morphemes look like massive evidence in favour of Eurasiatic at first glance. If valid, few linguists would have the right to doubt that a point has been made [...] However, closer inspection [...] shows too many misinterpretations, errors and wrong analyses [...] these allow no other judgement than that [Greenberg's] attempt to demonstrate the validity of his Eurasiatic has failed." In the 1980s, Russian linguist 's hypothesis () linking the Indo-European, Uralic, and Altaic (including Korean in his later papers) language families. Andreev also proposed 203 lexical roots for his hypothesized Boreal macrofamily. After Andreev's death in 1997, the Boreal hypothesis was further expanded by Sorin Paliga (2003, 2007). Pagel et al. In 2013, Mark Pagel, Quentin D. Atkinson, Andreea S. Calude, and Andrew Meade published statistical evidence that attempts to overcome these objections. According to their earlier work, most words exhibit a "half-life" of between 2,000 and 4,000 years, consistent with existing theories of linguistic replacement. However, they also identified some words – numerals, pronouns, and certain adverbs – that exhibit a much slower rate of replacement with half-lives of 10,000 to 20,000 or more years. Drawing from research in a diverse group of modern languages, the authors were able to show the same slow replacement rates for key words regardless of current pronunciation. They conclude that a stable core of largely unchanging words is a common feature of all human discourse, and model replacement as inversely proportional to usage frequency. Pagel et al. used hypothesized reconstructions of proto-words from seven language families listed in the Languages of the World Etymological Database (LWED). They limited their search to the 200 most common words as described by the Swadesh fundamental vocabulary list. Twelve words were excluded because proto-words had been proposed for two or fewer language families. The remaining 188 words yielded