1 MODELLING RELIGIOUS SIGNALLING A thesis submitted for the degree of Doctor of Philosophy at the Australian National University Carl Joseph Brusse February 2019 © Copyright by Carl Joseph Brusse, 2019 All Rights Reserved 2 3 This thesis is solely the work of its author. No part of it has been submitted for any degree, or is currently being submitted for any other degree. To the best of my knowledge, any help received in preparing this thesis, and all sources used, have been duly acknowledged. 4 5 for Caroline, Alida, and Isobel 6 7 ACKNOWLEDGEMENTS I owe a great debt to my supervisory panel members past and present: Kim Sterelny, Justin Bruner, Rachael Brown, and Ben Fraser, for their deeply insightful commentary and gentle corrective during the various phases of this project. In particular, Kim very much provided both the inspiration for this project and the impetus for venturing to return to philosophy for this PhD candidature. I would not have entered into this without his encouragement, and I certainly would not have made it out the other side without his support and mentorship. Thank you, Kim, for your judgment and generosity, and for your astute, necessity-sensitive application of patience (or lack thereof) when required. Justin too deserves special mention for patiently schooling me in evolutionary game theory and signalling games (despite my sometimes bizarrely misguided intuitions), and in suggesting and contributing to my first simulation projects and our joint paper at the 2016 PSA, published in Philosophy of Science. Being at the School of Philosophy at the ANU, the number of faculty and grad students (local and visiting) who have taken the time to listen and offer valuable insights would be too long to record here. A few of the locals who deserve special mention are Ste Mann, Chris Lean, Ron Planer, Anton Killin, Heather Browning, David Kalkman, Alex Sandgren, Dominie Dessaix, Donald Nordblom, Ross Pain, and Ten-Herng Lai. I would especially like to acknowledge Matt Spike for the many hours he spent sitting next to me, helping me get my most recent simulations to work. Other philosophers from here and elsewhere whose insights I have mined include Paul Griffiths, Emily Parke, Brett Calcott, Toby Handfield, Russell Grey, Kevin Zollman, Pierrick Bourratt, Colin Klein, Seth Lazar, Geoffrey Brennan, and Alan Hájek. Given the interdisciplinary features of this project, I have also been lucky enough to benefit from the intellectual generosity of many expert scholars in the science of religion, especially Joseph Bulbulia, Aiyana Willard, Eleanor Power, Martin Lang, Quentin Atkinson, John Shaver, and two anonymous reviewers from Religion, Brain and Behavior. Regarding material support, I must thank my current employer, the University of Sydney, and Professor Paul Griffiths in particular for his generosity, support and understanding over the last months of write-up. Thank you, Paul. The ANU’s support to me as student has included travel scholarships, and too many free meals to count as part of the ‘thesis boot camp’ and veterans’ days program. These are the sessions where much of this thesis was written up, along with 8 funded ‘shut up and write’ sessions organised by PARSA, and informal sessions organised by myself and others, including Adam Bugeja and Hanh Nguyen. The comradery and productivity of the group writing environment was a revelation. Finally, but most importantly, I want to thank my wife – Caroline Margaret Brusse. Without her encouragement and support I would not have started, continued, or finished this thesis. Her firm conviction that I could get it done, and her shouldering of disproportionate burdens and responsibilities while I flailed my way towards submission is the single most important reason it is now completed (and we can get something of our lives back). This dissertation is dedicated to her, and to our children Alida and Isobel, both of whom were born while it was being written. 9 10 11 ABSTRACT The origins of human social cooperation confound simple evolutionary explanation. But from Darwin and Durkheim onwards, theorists (anthropologists and sociologists especially) have posited a potential link with another curious and distinctively human social trait that cries out for explanation: religion. This dissertation explores one contemporary theory of the co-evolution of religion and human social cooperation: the signalling theory of religion, or religious signalling theory (RST). According to the signalling theory, participation in social religion (and its associated rituals and sanctions) acts as an honest signal of one’s commitment to a religiously demarcated community and its way of doing things. This signal would allow prosocial individuals to positively assort with one another for mutual advantage, to the exclusion of more exploitative individuals. In effect, the theory offers a way that religion and cooperation might explain one another, but which that stays within an individualist adaptive paradigm. My approach is not to assess the empirical adequacy of the religious signalling explanation or contrast it with other explanations, but rather to deal with the theory in its own terms – isolating and fleshing out its core commitments, explanatory potential, and limitations. The key to this is acknowledging the internal complexities of signalling theory, with respect to the available models of honest signalling and the extent of their fit (or otherwise) with religion as a target system. The method is to take seriously the findings of formal modelling in animal signalling and other disciplines, and to apply these (and methods from the philosophy of biology more generally) to progressively build up a comprehensive picture of the theory, its inherent strengths and weaknesses. The first two chapters outline the dual explanatory problems that cooperation and religion present for evolutionary human science, and surveys contemporary approaches toward explaining them. Chapter three articulates an evolutionary conception of the signalling theory, and chapters four to six make the case for a series of requirements, limitations, and principles of application. Chapters seven and eight argue for the value of formal modelling to further flesh out the theory’s commitments and potential and describe some simple simulation results which make progress in this regard. Though the inquiry often problematizes the signalling theory, it also shows that it should not be dismissed outright, and that it makes predictions which are apt for empirical testing. 12 13 CONTENTS 1. Cooperation and Religion: evolutionary approaches ................................................................ 14 1.1. Explaining costly behaviour .................................................................................................................................... 17 1.2. The problem of religion: maladaptation and cultural evolution .................................................................... 33 1.3. Timelines of emergence .......................................................................................................................................... 50 1.4. Summary and context .............................................................................................................................................. 60 2. Big Gods ....................................................................................................................................... 63 2.1. Overview of the big gods model: theory and mechanisms ............................................................................ 63 2.2. Predictions and evidence ........................................................................................................................................ 66 2.3. Connecting the conceptual and the empirical ................................................................................................... 74 2.4. Conclusions ................................................................................................................................................................ 79 3. Rationale for a signalling theory of religion ............................................................................... 81 3.1. The Signalling theory as an explanation .............................................................................................................. 83 3.2. Mechanism, endogeny, and scalability .................................................................................................................. 86 3.3. Functionalism and the scope for explanation .................................................................................................... 89 3.4. Summary ..................................................................................................................................................................... 92 4. Signalling theory for religious signalling .................................................................................... 95 4.1. Signals and signalling systems ................................................................................................................................. 95 4.2. Honesty in fakeable and unfakeable signals ...................................................................................................... 104 4.3. The problem with ‘costly signalling’ ................................................................................................................... 108 4.4. Why signalling theory matters