Modelling the evolution of socio- political complexity Submitted by Alice Jean Williams to the University of Exeter as a thesis for the degree of Doctor of Philosophy in Biological Sciences March 2019 This thesis is available for Library use on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. I certify that all material in this thesis which is not my own work has been identified and that no material has previously been submitted and approved for the award of a degree by this or any other University. Signature: ………………………………………………………….. 1 2 Abstract The level of organisation required to maintain cohesion in the vast societies we live in today is unprecedented in our past. In this thesis I look into why human societies began to shift from the small-scale groups which characterises the vast majority of human past, into the large-scale entities most of us currently live in. Several ideas have been proposed to explain why many different features of social complexity began to coalesce together in some areas of the world before others, each with some level of support from the archaeological record. In this thesis I have taken a different approach. I rigorously test one hypothesis for its logical consistency before applying it to archaeological data by formalising it as an agent-based model. The hypothesis described by Robert Carneiro (1970, 2012a) suggests that the more limited population movement is through environmental, resource, or social circumscription, the more likely complex societies are to form. By constructing agent-based models from this hypothesis I can show the conditions under which this statement is true, and have identified several areas where assumptions were not made explicit in the original hypothesis. By adapting the models to correspond with the conditions of the Valley of Oaxaca in highland Mexico, I show the extent to which the circumscription theory may explain the emergence of social complexity there and where the gaps in our knowledge lie. In creating and testing an agent- based model of the circumscription hypothesis I have shown how agent-based models may be used in archaeology to deepen our understanding of verbal theories and identified conditions which could have intensified the emergence of complex societies around the world. 3 Acknowledgements “You are here to learn the subtle science and exact art of potion-making.” Severus Snape, in Harry Potter and the Philosopher’s Stone (J. K. Rowling, 1997). I have learnt that building an agent-based model from scratch is a craft which requires endless patience. Nothing is so humbling, as having the computer fling Every. Single. Error. that you yourself wrote into the code back at you. I would therefore like to thank my supervisors Alex Mesoudi and Andy Young for nudging me along this very winding and challenging journey with great wisdom and patience. Thank you also to Lacey Carpenter, for welcoming me on excavation at El Palenque, and to the staff at both the Royal Cornwall Museum in Truro and the National Museum of Scotland in Edinburgh, for letting me dose up on some archaeology away from the computer. The research and placements I undertook would not have been possible without funding from NERC GW4+ DTP. “For every task that must be done, there is an element of fun. Find the fun, and SNAP! The job’s a game!” Mary Poppins (Disney, 1964) There is an element of fun in everything. I would like to thank a very long list of people for helping me find the fun when I struggled to see it myself. In no particular order, but grouped roughly by when and where I met you, I’d like to thank you all. Beth Clark, Paula Marjamäki, and Ian Skicko, you’ve been wonderful housemates and fellow PhD warriors. You have all picked me up whenever I’ve fallen flat, especially you Beth. My turn to be your champion! Lewis Bartlett, you have your own sentence to thank you for your absolute belief in me from the start. Adam Flitton, thank you for steadfastly putting up with my random nonsense and helping me in moments of utter exasperation. Lotty Brand, your good humour is infectious. Thank you for being so persistently optimistic and interested in my strange research endeavours. Emma Wood, art buddy, thank you for reassuring me that my writing was not as dire as I thought. Becky Boulton and Paul Davison, you swooped in and gave me perspective from the Land Beyond Thesis when I needed it most. For everyone I have ever had the pleasure of sharing an office with, thank you for the tea and company. 4 To anyone I’ve not mentioned here, you are not forgotten. You have all helped me out in some way, shape, or form, so thank you. My glowing thanks and love are for you, my kin of life and genes. Ellie Shelley, Emily Ryley, and Kate Grant, you are the friends for whom time does not matter. Kate, who would’ve thought our lives would be so closely entwined over such distances? Ethel Burns, I am privileged to call you my Godmother. No one could ask for a more powerful role model. Stuart Williams, my affable, wonderful brother, the bafflement most certainly won’t stop here. Janice and Jerry Williams, the best of parents, your unwavering love and support is the greatest comfort for me. I would be a husk of a person without you all. You have my love. Always. Brenda Eaton, Grandma, I think of you particularly. Your name would have adorned the title page of your own thesis had times been different and our lives reversed. "Words are, in my not so humble opinion, our most inexhaustible source of magic, capable of both inflicting injury and remedying it." Albus Dumbledore, in Harry Potter and the Deathly Hallows, Part II (2011) A thank you must also go to all the fiction and music that will forever keep me going. The power of a story, and the words we choose to tell it with, cannot ever be underestimated. I hope that you, reader, may find some interest and amusement in these pages. So onwards with the thesis! 5 Contents Abstract .............................................................................................................. 3 Acknowledgements ............................................................................................ 4 Contents ............................................................................................................. 6 Table list ........................................................................................................... 12 Figure list .......................................................................................................... 13 Overview .......................................................................................................... 17 Chapter 1: What is social complexity and why did it emerge in some human societies? ........................................................................................... 18 1.1 Introduction ................................................................................................. 19 1.2 What is social complexity? ......................................................................... 19 1.3 How can we measure social complexity? ................................................... 23 1.3.1 Size ............................................................................................................................... 24 1.3.2 Power differentiation .................................................................................................. 25 1.3.3 Organisation ................................................................................................................ 26 1.3.4 The measure of social complexity used in this thesis ........................................... 28 1.4 What causes social complexity to increase? .............................................. 29 1.5 Circumscription theory ................................................................................ 33 1.5.1 Archaeological evidence............................................................................................ 36 1.5.2 If there is environmental circumscription, is there also evidence of polity formation? .............................................................................................................................. 36 1.5.3 Is it possible to have social circumscription in areas without high resource concentration? ....................................................................................................................... 39 1.5.4 What can be concluded about the potential of the circumscription hypothesis to explain social complexity formation? ................................................................................. 39 1.5.5 Limitations of the circumscription hypothesis ......................................................... 40 1.6 Agent-based modelling ............................................................................... 41 1.7 Aim of this thesis ........................................................................................ 42 6 Chapter 2: How can agent-based models be used as an archaeological tool to investigate the emergence of social complexity? ........................... 43 2.1 Introduction: formal models ........................................................................ 44 2.2 Agent-based models (ABMs) ...................................................................... 46 2.2.1 Emergence of complex phenomena ........................................................................ 47 2.2.2 Scale ............................................................................................................................