the development of behavioral modernity toward the end of the Middle Paleolithic or at the beginning of the Upper Paleolithic, roughly 50,000 years ago. Thus, in the opinion of Richard Klein, the ability to produce complex speech only developed some 50,000 years ago (with the appearance of modern humans or Cro-Magnons). Johanna Nichols (1998) argued that vocal languages must have begun diversifying in our species at least 100,000 years ago. In 2011, an article in the journal Science proposed an African origin of modern human languages. It was suggested that human language predates the out-of-Africa migrations of 50,000 to 70,000 years ago and that language might have been the essential cultural and cognitive innovation that facilitated human colonization of the globe. In Perreault and Mathew (2012), an estimate on the time of the first emergence of human language was based on phonemic diversity. This is based on the assumption that phonemic diversity evolves much more slowly than grammar or vocabulary, slowly increasing over time (but reduced among small founding populations). The largest phoneme inventories are found among African languages, while the smallest inventories are found in South America and Oceania, some of the last regions of the globe to be colonized. The authors used data from the colonization of Southeast Asia to estimate the rate of increase in phonemic diversity. Applying this rate to African languages, Perreault and Mathew (2012) arrived at an estimated age of 150,000 to 350,000 years, compatible with the emergence and early dispersal of H. sapiens. The validity of this approach has been criticized as flawed. Characteristics Speculation on the "characteristics" of Proto-World is limited to linguistic typology, i.e. the identification of universal features shared by all human languages, such as grammar (in the sense of "fixed or preferred sequences of linguistic elements"), and recursion, but beyond this nothing can be known of it. Christopher Ehret has hypothesized that Proto-Human had a very complex consonant system, including clicks. A few linguists, such as Merritt Ruhlen, have suggested the application of mass comparison and internal reconstruction (cf. Babaev 2008). A number of linguists have attempted to reconstruct the language, while many others reject this as fringe science. Vocabulary Ruhlen tentatively traces a number of words back to the ancestral language, based on the occurrence of similar sound-and-meaning forms in languages across the globe. Bengtson and Ruhlen identify 27 "global etymologies". The following table lists a selection of