The term Proto-World language refers to the hypothetical, most recent common ancestor of all the world's languages – an ancient proto-language from which are derived all modern languages, all language families, and all dead languages known from the past 6,000 years of recorded history.
In such a scenario, Proto-World would spread from a small population out to other human populations long after they separated. Note also that it would not necessarily be the first language spoken altogether, but only the latest common ancestor of all languages known today, and already may have looked back on a long evolution, and even may have existed alongside other languages of which no trace survived into historical times. For example, it is disputed whether Homo neanderthalensis had the faculty of speech. If they did, their language in all probability would not have been derived from Proto-World as defined above. Furthermore, if they had a language, this would substantiate the claim for the existence of Proto-World, without making any prediction as to its form, because it would imply that the origin of language predates human phylogenetic separation.
Many question the underlying theory of monogenesis, the assumption that all known languages do derive from a common ancestor, suggesting that language may have developed independently in different groups of early humans from proto-linguistic means of communication, thereby disputing the existence of Proto-World, or at least shifting focus to glottogonic issues. This debate is essentially about the definition of the term language, and about whether the system of communication employed by human beings at the time of Mitochondrial Eve qualifies as a language in the narrow sense.
Drawing on the works of Vladislav Illich-Svitych, the American linguist Joseph Greenberg claimed that long-distance relationships can be shown by applying a controversial approach he called "mass lexical comparison". The languages are compared by using a limited set of words (including function words and affixes) simply by means of counting cognates. He used this method to establish a classification of African languages. His work has generated considerable interest outside the linguistic community. It is still much debated.
Sergei Starostin cautiously suggested a number of roots from the "Borean language" - the hypothetical ancestor of different language families of the northern hemisphere; possible etymological matches between what he considered the five major macrofamilies of the Old World, Eurasiatic, Afroasiatic, Sino-Caucasian and Austric with potential parallels from Amerind and several African language families added, but noting that it is still much too early to talk of a reconstructed "Proto-Borean" language, let alone Proto-World.
Merritt Ruhlen is one of the most vocal and controversial supporters of the Proto-World hypothesis.
The following table shows some roots in various language families which show similarities. The symbol V stands for a vowel.
Some of the Indo-European words that come from words in this table are qui (Latin), who, aqua (Latin), digit, bough (from the root bhāghu- meaning elbow or shoulder), fud (dialectal English for vulva).
Based on these correspondences, linguist Merritt Ruhlen has developed a table of basic words in Proto World:
Critics say that from a purely statistical point of view, even among any two unrelated languages, there will most likely be a number of similar-sounding words with similar meanings (see also Swadesh list).
In addition, situations are conceivable in which a completely new language may have arisen even at later times. There is no known instance of such an event for spoken languages, but the Nicaraguan Sign Language is an example of a non-articulate language which arose naturally among deaf children raised by hearing parents However some consider Nicaraguan Sign Language to be an invalid example of spontaneous language generation since pre-existing gestures used by the surrounding hearing-capable population may likely have been its basis. There is no known fully developed spoken language that has emerged spontaneously from a non-speaking population.