William Croft 

(Univ of New Mexico)
Human language evolved, and human languages also evolve. Although we have virtually no empirical evidence about prior stages of the evolution of the human language capacity, we have abundant evidence about how human languages evolve. Yet evolutionary thinking has not been found in the study of language change until recently. 

The fields of historical linguistics and sociolinguistics have studied language change processes. These disparate and disconnected approaches to the study of language change can be integrated in an evolutionary framework. First, language change, like other evolutionary processes, is a two-step process: the generation of variation and the selection of variants. Traditional historical linguistics focuses on how innovations arise (generation of variation); sociolinguistics on how variants are propagated through a speech community (selection). Second, language change takes place via language use. That is, evolution of linguistic forms occurs each time a linguistic form is used. In evolutionary terms, the linguistic form, or more precisely a particular token of use of a linguistic form, is the replicator in the evolutionary process of language change. Following David Hull's General Analysis of Selection, I have argued that the speaker functions as interactor, functioning as the means both of generating variation in replicators and of selection of replicators, leading to language change. Language and language change is an example of cultural transmission, and other processes of cultural transmission can be modeled in the same way.

Selection in language change, that is, propagation of linguistic variants in a speech community, is a fundamentally social process, and the dynamics of interaction between speakers (interactors) and language forms in use (replicators) provides a rich theory of how selection can operate in cultural evolution. Generation of variation is a type of creativity, the theme of this summerschool. Variation in language change can only be understood in the context of the joint cooperative activity between humans that language helps to achieve. As a result, the mapping between language form and meaning is fundamentally indeterminate. The variation generated via language use in a social context  is the source of language change.

An evolutionary framework for language change provides a unified approach to language, a potential model for more general theories of cultural transmission and contributes to understanding the coevolution of modern humans and our cultural behaviors such as language.