The Proto-Human language (also Proto-Sapiens, Proto-World) is the hypothetical direct genetic predecessor of all the world's spoken languages. It would not be ancestral to sign languages. The concept is speculative and not amenable to analysis in historical linguistics. It presupposes a monogenetic origin of language, i.e. the derivation of all natural languages from a single origin, presumably at some time in the Middle Paleolithic period. As the predecessor of all extant languages spoken by modern humans (Homo sapiens), Proto-Human language as hypothesised would not necessarily be ancestral to any hypothetical Neanderthal language. Terminology There is no generally accepted term for this concept. Most treatments of the subject do not include a name for the language under consideration (e.g. Bengtson and Ruhlen). The terms Proto-World and Proto-Human are in occasional use. Merritt Ruhlen used the term Proto-Sapiens. History of the idea The first serious scientific attempt to establish the reality of monogenesis was that of Alfredo Trombetti, in his book L'unità d'origine del linguaggio, published in 1905. Trombetti estimated that the common ancestor of existing languages had been spoken between 100,000 and 200,000 years ago. Monogenesis was dismissed by many linguists in the late 19th and early 20th centuries, when the doctrine of the polygenesis of the human races and their languages was widely popularised. The best-known supporter of monogenesis in America in the mid-20th century was Morris Swadesh. He pioneered two important methods for investigating deep relationships between languages, lexicostatistics and glottochronology. In the second half of the 20th century, Joseph Greenberg produced a series of large-scale classifications of the world's languages. These were and are controversial but widely discussed. Although Greenberg did not produce an explicit argument for monogenesis, all of his classification work was geared toward this end. As he stated: "The ultimate goal is a comprehensive classification of what is very likely a single language family." Notable American advocates of linguistic monogenesis include Merritt Ruhlen, John Bengtson, and Harold Fleming. Date and location The first concrete attempt to estimate the date of the hypothetical ancestor language was that of Alfredo Trombetti, who concluded it was spoken between 100,000 and 200,000 years ago, or close to the first emergence of Homo sapiens. It is uncertain or disputed whether the earliest members of Homo sapiens had fully developed language. Some scholars link the emergence of language proper (out of a proto-linguistic stage that may have lasted considerably longer) to