Minimal requirements for the cultural evolution of language
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Spike, Matthew John
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Human language is both a cognitive and a cultural phenomenon. Any evolutionary account of language, then, must address both biological and cultural evolution. In this thesis, I give a mainly cultural evolutionary answer to two main questions: firstly, how do working systems of learned communication arise in populations in the absence of external or internal guidance? Secondly, how do those communication systems take on the fundamental structural properties found in human languages, i.e. systematicity at both a meaningless and meaningful level? A large, multi-disciplinary literature exists for each question, full of apparently conflicting results and analyses. My aim in this thesis is to survey this work, so as to find any commonalities and bring this together in order to provide a minimal account of the cultural evolution of language. The first chapter of this thesis takes a number of well-established models of the emergence of signalling systems. These are taken from several different fields: evolutionary linguistics, evolutionary game theory, philosophy, artificial life, and cognitive science. By using a common framework to directly compare these models, I show that three underlying commonalities determine the ability of any population of agents to reliably develop optimal signalling. The three requirements are that i) agents can create and transfer referential information, ii) there is a systemic bias against ambiguity, and iii) some mechanism leading to information loss exists. Following this, I extend the model to determine the effects of including referential uncertainty. I show that, for the group of models to which this applies, this places certain extra restrictions on the three requirements stated above. In the next chapter, I use an information-theoretic framework to construct a novel analysis of signalling games in general, and rephrase the three requirements in more formal terms. I then show that we can use these 3 criteria as a diagnostic for determining whether any given signalling game will lead to optimal signalling, without the requirement for repeated simulations. In the final, much longer, chapter, I address the topic of duality of patterning. This involves a lengthy review of the literature on duality of patterning, combinatoriality, and compositionality. I then argue that both levels of systematicity can be seen as a functional adaptation which maintains communicative accuracy in the face of noisy processes at different levels of analysis. I support this with results from a new, minimally-specified model, which also clarifies and informs a number of long-fought debates within the field.