There is increasing recognition that both individual and cultural processes play a role in the evolution of language, but it is not clear how these interact. Silent gesture, an experimental paradigm in which adult hearing participants describe events using only their hands, can help us discover the individual biases that play a role when no conventional communication system is in place. When people improvise to convey information in this way, the gestures they produce will show variability that is dependent on the semantic properties of the meaning to be conveyed. Conventional languages, by contrast, are typically more systematic and regular.

Understanding the transition from improvised variability to conventionalised regularity is a major goal of language evolution research. I will present our recent work that extends the silent gesture paradigm, to show how individuals improvise solutions to communicative challenges, how pairs of individuals create conventions through interaction, and how these conventions are transmitted over time through learning.

I will focus on the emergence of two linguistic features: (1) systematic structure in the lexical domain, and (2) basic word order conventions. Surprisingly, these two features seem to prefer different circumstances for their emergence. While systematic structure crucially emerges when interaction and cultural transmission are combined, word order conventions do not depend on transmission (a pattern that is consistent with recent findings in Nicaraguan Sign Language).

I will reflect on how different aspects of language are the result of cognitive biases in individuals and mechanisms of cultural evolution - in different ways.