"Their primary source of information was a detailed ethnographic description of over 1,200 language groups across the world." This method could be extremely er

"Their primary source of information was a detailed ethnographic description of over 1,200 language groups across the world." This method could be extremely error-prone, due to borrowings, etc. between languages, e.g. see some of the criticisms against gluttochronology (http://en.wikipedia.org/wiki/Glottochronology#Discussion http://en.wikipedia.org/wiki/Glottochronology#Discussion) which uses similar techniques to determine relation between languages.