Zuidema, Willem Hero. “The major transitions in the evolution of language.” PhD diss., University of Edinburgh, 2005.
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The origins of human language, with its extraordinarily complex structure and multitude of functions, remains among the most challenging problemsfor evolutionary biology and the cognitive sciences. Although many will agree progress on this issue would have important consequences for linguistic theory, many remain sceptical about whether the topic is amenable to rigorous, scientific research at all. Complementing recent developments toward better empirical validation, this thesis explores how formal models from both linguistics and evolutionary biology can help to constrain the many theories and scenarios in this field. I first review a number of foundational mathematical models from three branches of evolutionary biology – population genetics, evolutionary game theory and social evolution theory – and discuss the relation between them. This discussion yields a list of ten requirements on evolutionary scenarios for language, and highlights the assumptions implicit in the various formalisms. I then look in more details at one specific step-by-step scenario, proposed by Ray Jackendoff, and consider the linguistic formalisms that could be used to characterise the evolutionary transitions from one stage to the next. I conclude from this review that the main challenges in evolutionary linguistics are to explain how three major linguistic innovations – combinatorial phonology, compositional semantics and hierarchical phrase-structure – could have spread through a population where they are initially rare. In the second part of the thesis, I critically evaluate some existing formal models of each of these major transitions and present three novel alternatives. In an abstract model of the evolution of speech sounds (viewed as trajectories through an acoustic space), I show that combinatorial phonology is a solution for robustness against noise and the only evolutionary stable strategy (ESS). In a model of the evolution of simple lexicons in a noisy environment, I show that the optimal lexicon uses a structured mapping from meanings to sounds, providing a rudimentary compositional semantics. Lexicons with this property are also ESS’s. Finally, in a model of the evolution and acquisition of context-free grammars, I evaluate the conditions under which hierarchical phrase-structure will be favoured by natural selection, or will be the
outcome of a process of cultural evolution. In the last chapter of the thesis, I discuss the implications of these models for the debates in linguistics on innateness and learnability, and on the nature of language universals. A mainly negative point to make is that formal learnability results cannot be used as evidence for an innate, language-specific specialisation for language. A positive point is that with the evolutionary models of language, we can begin to understand how universal properties and tendencies in natural languages can result from the intricate interaction between innate learning biases and a process of cultural evolution over many generations.