Language Evolution and Computation Bibliography

For a long time, human language has been assumed to be genetically determined and therefore the product of biological evolution. It is only within the last decade that researchers have begun to investigate more closely the domain-general cognitive mechanisms of cultural evolution as an alternative explanation for the origins of language. Most of this more recent work focuses on the role of imperfect cultural transmission and abstracts away from the mechanisms of communication. Specifically, models developed to study the cultural evolution of language ''both theoretical and computational ''often tacitly assume that linguistic signals fully specify the meaning they communicate. They imply that ignoring the fact that this is not the case in actual language use is a justified idealisation which can be made without significant consequences. In this thesis, I show that by making this idealisation, we miss out on the extensive explanatory potential of an empirically attested property of language: its pragmatic plasticity. The meaning that a signal comes to communicate in a specific context usually differs to a certain degree from its conventional meaning. This thesis (i) introduces a model of the cultural evolution of language that acknowledges and incorporates the fact that communication exhibits pragmatic plasticity and (ii) explores the explanatory potential of this fact with regard to language evolution.

The thesis falls into two parts. In the first part, I develop the model conceptually. I begin by analysing the components of extant models of general cultural evolution and discuss how models of language change and linguistic evolution map onto them. Innovative use is identified as the motor of cultural evolution. I then conceptualise the cognitive mechanisms underlying innovative language use and argue that they originate in pre-linguistic forms of ostensive-inferential communication. In a next step, the identified mechanisms are employed to provide a unified account of the two main explananda of evolutionary linguistics, the emergence of symbolism and the emergence of grammar. Finally, I discuss the implications of the presented analysis for the so-called proto-language debate. In the second part of the thesis, I propose a computational implementation of the developed conceptual model. This computational implementation allows for the simulation of the cultural emergence and evolution of symbolic communication and provides a laboratory-like environment to study individual aspects of this process. I employ such computer simulations to explore the role that pragmatic plasticity plays in the development of the expressivity, signal economy and ambiguity of emerging and evolving symbolic communication systems.

As its main contribution to the study of language evolution, this thesis shows that a model of linguistic cultural evolution that incorporates the notion of pragmatic plasticity has the potential to explain two crucial evolutionary puzzles, namely (i) how language can emerge from no language, and (ii) how language can come to exhibit the appearance of design for communication. The proposed usage-based model of language evolution bridges the evolutionary gap between no language and language by identifying ostensive-inferential communication as the continual aspect present in both stages, and by demonstrating that the cognitive mechanisms involved in ostensive-inferential communication are sufficient for the transition from one stage to the other.

Computational modelling has proven a useful method to study the emergence of language-like communication systems. However, most existing models abstract away from the two facts that (1) lan- guage use exhibits pragmatic plasticity1 and (2) linguistic knowledge is an integral part of human conceptual knowledge. This paper introduces a basic architecture for a model that overcomes these shortcomings by incorporating elements of Relevance Theory and Cognitive Semantics.

Traditionally, grammaticalisation has been described as being based on phenomena specific to language such as metaphorical extension or reanalysis. This characterisation is somewhat in contrast to claims that grammaticalisation is involved in the much more general process of the initial emergence of language. In this article, we provide a unified analysis of both the metaphor-based and the reanalysis-based account of grammaticalisation which is grounded in the cognitive mechanisms underlying ostensive-inferential communication. We are thus able to show that the process of grammaticalisation is an instantiation of a domain-general pre-linguistic phenomenon.

We argue that studying grammaticalisation is useful to evolutionary linguists, if we abstract away from linguistic description to the underlying cognitive mechanisms. We set out a unified approach to grammaticalisation that allows us to identify these mechanisms, and argue that they could indeed be sufficient for the initial emergence of linguistic signal-meaning associations.

Ambiguity is a defining property of natural language distinguishing it from artificial languages. It would seem to be dysfunctional, and therefore its ubiquity in language poses an evolutionary puzzle. This paper discusses the implications of a typical iterated learning model on the conditions under which syntactic ambiguity emerges and stabilises in language. It contrasts the purely nativist stance that language imperfections such as syntactic ambiguity are artifacts arising from internal constraints of the genetically determined language faculty with the view that they are frozen accidents persisting because they are easily learnt.