The Persistence of a Local Dialect When a National Standard Language is Present: An Evolutionary Dynamics Model of Cultural Diversity

Cinthia M. Tanaka, Joung-Hun Lee, Yoh Iwasa

In recent decades, cultural diversity loss has been a growing issue, which can be analyzed mathematically through the use of the formalism of the theory of cultural evolution. We here study the evolutionary dynamics of dialects in order to find the key processes for mitigating the loss of language diversity. We define dialects as different speech systems of the same language which are mutually intelligible. Specifically, we focus on the survival of a local dialect when competing against a national standard language, with the latter giving an advantage in occupational and economic contexts. We assume individuals may use different dialects, in response to two different situations: they may use the national language in a formal workplace, while they may use a local dialect in family or close friend meetings. We consider the choice of a dialect is guided by two forces: (1) differential attractiveness of the local/standard language and (2) willingness to speak the same dialect (conformity factor) inside a private group. We found that the evolutionary outcome critically depends on how conformity works. Conformity enhances the effect of differential attractiveness between the local dialect and the standard language if conformity works favoring only those states in which all speakers use the same dialect (unanimity pressure model), but conformity has no effect at all if it works in proportion to the fraction among peers (peer pressure model).