Self-domestication and Language Evolution James Geoffrey Thomas BSc, MA, MSc A thesis submitted in fulfilment of requirements for the degree of Doctor of Philosophy to Linguistics and English Language School of Philosophy, Psychology and Language Sciences University of Edinburgh 25th September 2013 i Declaration I hereby declare that this thesis is of my own composition, and that it contains no material previously submitted for the award of any other degree. The work reported in this thesis has been executed by myself, except where due acknowledgement is made in the text. James Geoffrey Thomas ii Dedication To Barbara Scholz, much missed, who was wonderfully critical of my work and wonderfully uncritical of me. iii Acknowledgements I thank my supervisors, Simon Kirby, Richard Shillcock and Barbara Scholz, for many years of sustained guidance, support and encouragement. I would also like to thank all the members of the Language Evolution and Computation Research Unit, past and present, for providing a continuously supportive and stimulating intellectual environment. I have learned much from many of you, both in formal talks and casual conversations. Special thanks are also owed to Erin Brown, Thom Scott-Phillips and Bill Thompson, each of whom provided invaluable feedback on one or more chapters of the thesis. Finally, none of this would have been possible, from undergraduate onwards, without the continuous support of my parents. It is not only the shoulders of giants on which we stand. iv Abstract This thesis addresses a major problem facing any attempt to account for language structure through a cultural mechanism: The processes required by such a mechanism are only possible if we assume the existence of a range of preconditions. These preconditions are not trivial, and themselves require an explanation. In this thesis I address the nature and origin of these preconditions. I approach this topic in three stages. In the first stage, I pull-apart the functioning of one prominent cultural account of language evolution—the Iterated Learning Model —to identify the preconditions it assumes. These preconditions cluster into two main groups. The first concerns the traditional transmission of the communication system. The second relates to the emergence of particular skills of social cognition that make learned symbols and language-like communication a possibility. In the second stage, I turn to comparative evidence, looking for evolutionary analogies that might shed light on the emergence of these preconditions. Two case studies—the Bengalese finch and the domestic dog—are considered in detail, both of which show aspects of one of the preconditions emerging in the context of domestication. In each case I examine what it is about the domestication process that led to this outcome. In the final stage, I consider whether this same context might explain the emergence of these preconditions in humans. The claim that humans are a self-domesticated v species has a long history, and is increasingly invoked in contemporary discussions of language evolution. However, it is often unclear exactly what this claim entails. I present a synthesis and critique of a range of empirical and theoretical perspectives on self-domestication. I conclude that human self-domestication is a coherent concept, and that there are several plausible accounts of how it might have occurred. The realisation that humans are a self-domesticated species can, therefore, provide some insight into how a cultural account of language structure might be possible at all. vi Contents Declaration.................................................................................................................................i Dedication.................................................................................................................................ii Acknowledgements..................................................................................................................iii Abstract....................................................................................................................................iv Contents..................................................................................................................................vi List of Tables..........................................................................................................................xiv List of Figures.........................................................................................................................xv Introduction – Self-domestication and Language Evolution...................................1 I. Language evolution.........................................................................................................3 i. The scope of the thesis.....................................................................................................3 ii. Approaches to language evolution...................................................................................5 iii. Cultural and biological accounts......................................................................................7 II. Self-domestication..........................................................................................................9 III. Self-domestication and language evolution.............................................................11 IV. Chapter plan.................................................................................................................12 Chapter 1 – The Iterated Learning Model and its Preconditions….......................13 1.1 – Formalism, functionalism and the ILM ….......................................................13 1.2 – Biological accounts and the linkage problem..............................................15 1.2.1 – The linkage problem...............................................................................................15 1.2.2 – Natural selection and the linkage problem.............................................................16 1.2.3 – Extra-biological regularities in evolution.................................................................21 1.3 – Cultural accounts and the linkage problem..........................................................23 vii 1.3.1 – Iterated learning I: simulations...............................................................................24 1.3.2 – Iterated learning II: experiments............................................................................30 1.3.3 – Summary................................................................................................................36 1.4 – Evolutionary preconditions of the ILM.................................................................39 1.4.1 – The ability to acquire new signals.........................................................................40 1.4.2 – The ability to acquire and produce new signal-meaning associations..................43 1.4.3 – The ability to infer communicative intent...............................................................44 1.4.4 – The existence of a bottleneck................................................................................47 1.4.5 – The existence of the expressivity pressure............................................................48 1.4.5.1 – Why communicative function? Natural selection as a seductive solution.....................49 1.4.5.2. – Problems with that seductive solution: bootstrapping and foresight............................50 1.4.5.3 – Models of linguistic communication I: The code model...............................................53 1.4.5.4 – Models of linguistic communication II: The ostensive-inferential model........................55 1.4.5.5 – Relevance theory..................................................................................................56 1.4.5.6 – The expressivity pressure in light of relevance theory................................................60 1.5 – The role of natural selection in cultural accounts of language structure.........63 1.6 – The complementarity of the ILM and pragmatic approaches to language......66 1.7 – Conclusions..............................................................................................................67 1.7.1 – How does the ILM work?.......................................................................................67 1.7.2 – What are its necessary preconditions?..................................................................69 Chapter 2 – Traditional Transmission and the Bengalese Finch..........................73 2.1 – The logic of evolutionary comparisons..........................................................74 2.2 – The Bengalese finch and the white-rumped munia: the differences.....76 2.2.1 – Brief historical account...........................................................................................76 2.2.2 – Dimensions of learning in songbirds......................................................................77 2.2.2.1 – When song is learned............................................................................................77 viii 2.2.2.2 – The necessity of early experience...........................................................................78 2.2.2.3 – The importance of social experience.......................................................................79 2.2.2.4 – The number of songs learned.................................................................................79 2.2.2.5 – Copying fidelity of learners.....................................................................................80