Language is the primary repository and mediator of human collective knowledge. A central question for evolutionary linguistics is the origin of the combinatorial structure of language (sometimes referred to as dual- ity of patterning), one of language’s basic design features. Emerging sign languages provide a promising arena to study the emergence of language properties. Many, but not all such sign languages exhibit combinatori- ality, which generates testable hypotheses about its source. We hypoth- esise that combinatoriality is the inevitable result of learning biases in cultural transmission, and that population structure explains differences across languages. We construct an agent-based model with population turnover. Bayesian learning agents with a prior preference for compress- ible languages (modelling a pressure for language learnability) commu- nicate in pairs under pressure to reduce ambiguity. We include two trans- mission conditions: agents learn the language either from the oldest agent or from an agent in the middle of their lifespan. Results suggest that (1) combinatoriality emerges during iterated cultural transmission under concurrent pressures for simplicity and expressivity; and (2) population dynamics affect the rate of evolution, which is faster when agents learn from other learners than when they learn from old individuals. This may explain its absence in some emerging sign languages. We discuss the con- sequences of this finding for cultural evolution, highlighting the interplay of population-level, functional and cognitive factors.
|Journal||Philosophical Transactions of the Royal Society B: Biological Sciences|
|Publication status||Accepted/In press - 2 Jul 2021|