Abstract
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 duality 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 combinatoriality, which generates testable hypotheses about its source. We hypothesize 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 compressible languages (modelling a pressure for language learnability) communicate in pairs under pressure to reduce ambiguity. We include two transmission 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 consequences of this finding for cultural evolution, highlighting the interplay of population-level, functional and cognitive factors.This article is part of a discussion meeting issue ‘The emergence of collective knowledge and cumulative culture in animals, humans and machines’.
Highlights
Humans use language daily throughout their lives
Since we are using a simplicity prior, it makes sense that the simplest languages will dominate. To put it another way, the easiest languages to learn in the set of possible languages are the degenerate ones, and since the only pressure on the languages being transmitted is that they be learned each generation, the tendency will be for languages to adapt to be more learnable through cultural evolution
Our simulation results lend support to the idea that the cultural evolution of language gives rise to the kind of structure we see as typifying human language
Summary
Humans use language daily throughout their lives. Language is a key repository and the primary mediator of collective knowledge in our species. Languages used by larger communities, covering larger geographical areas with a higher degree of contact with other languages, tend to be simpler than those used in smaller, more close-knit populations [4,20,21,22,23,24,25,26,27,28,29,30] This has been suggested to derive from the presence of adult, non-native language learners [4,31]. Each sign in ABSL appears to be built not from a recombination of phonological elements that robustly reoccur across a wide set of distinct lexical items, but rather as a non-decomposable whole, demonstrating that duality of patterning is not an inescapable consequence of the existence of a communication system.
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