Trees, Waves and Linkages: Models of Language Diversification 1 on the Diversification of Languages 1.1 Language Extinction, Language Emergence

The number of languages spoken on the planet has oscillated up and down throughout the history of mankind. 1 Different social factors operate in opposite ways, some resulting in the decrease of language diversity, others favouring the emergence of new languages. Thus, languages fade away and disappear when their speakers undergo some pressure towards abandoning their heritage language and replacing it in all contexts with a new language that is in some way more socially prominent (Simpson, this volume). The process of language extinction may be rapid or slow, and varies in intensity depending on historical circumstances. While this process results in the erosion of language diversity, others bring about the opposite result: an increase in the number of spoken languages. Because no natural language appears ex nihilo, one has to explain how new languages emerge out of older ones. Some – such as pidgins and creoles (Romaine 1988, Siegel 2004) or mixed languages (Matras & Bakker 2003) – result historically from the encounter of two populations who were driven, under very special social conditions, to combine elements of their respective languages and create a new one. Yet this pattern, whereby a language is born of two parents, is not the typical scenario. New languages also commonly arise from the internal diversification of a single language as it evolves into separate daughter languages over time, following processes where external input does not necessarily play the central role. This phenomenon of internal diversification is the object of the present chapter. The two tendencies outlined above – language extinction and language emergence – have always occurred in human history; 2 yet in terms of scientific knowledge, the modern scholar is faced here with a strong asymmetry. Except for the few that have left behind written materials that can be deciphered, most extinct languages of the past will forever be unknown, whether in their linguistic structures or the social causes of their demise. By contrast, linguistic diversification has brought about an observable outcome, in the form of attested languages. The latter can be analysed and compared in a historical perspective,