Abstract
In this talk we suggest that the constraints on language processing and planning imposed by the structuring of interaction into turns at talk can affect the evolution of structural features of languages, such as basic word order. Speakers strive to reduce gaps and overlap between turns at talk (Sacks, Schegloff & Jefferson, 1974). Indeed, most gaps between turns are shorter than the minimum reaction time from planning to speak to actually speaking, suggesting that speakers project turn endings, and begin planning responses before the previous turn has ended. Recent research has demonstrated variation in the timing of turn-taking between speakers of different languages (Stivers et al., 2009). There is also variation between languages in the structure of individual turns, such as the basic order of subject, object and verb. There may be links between these two phenomena (Schegloff, 1996), mediated by the speaker’s planning of an utterance or the listener’s projection of the utterance. For instance, in Japanese, the verb appears at the end of an utterance, making projection difficult for the listener (Tanaka, 2000). Interestingly, the shortest average gaps occur for a verb-initial language (Tzeltal), which should make planning for the speaker difficult.
We take a cultural evolutionary approach to this puzzle. If the basic timing of turn-taking is a fundamental principle of human languages (Levinson, 2006), then linguistic structures may have adapted to the constraints of turn-taking. For example, if the verb provides the syntactic frame for a sentence, then its position in the sentence might adapt to several pressures: verbs in final position give speakers more time to plan the most complex component of the turn; verbs in initial position allow recipients to project the shape of the turn relatively early. If speakers use the same configuration in a sequence of turns, then the amount of time for planning between each turn is optimised – what we call the principle of symmetry. Another constraint is that verbs in medial position are less vulnerable to overlap on the margins of the turn.
We present a cultural evolutionary model as a proof of this concept. While many explanations of the origins and structure of language focus on constraints on individual cognition, this hypothesis suggests that constraints of interaction between individuals can also shape the distribution of structural features that we observe in the world’s languages.
