The Evolution of Human Post-Marital Residence
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The evolution of human post-marital residence A thesis submitted to the University of Manchester for the degree of Master of Philosophy in Bioarchaeology in the Faculty of Science and Engineering 2016 Edith Invernizzi School of Earth and Environmental Sciences List of contents List of content p. 2 List of tables p. 4 List of figures p. 5 Abstract p. 6 Declaration p. 7 Copyright statement p. 7 Acknowledgements p. 8 CHAPTER I p. 9 1.1 A brief overview of human residence strategies p. 10 1.2 Factors in the emergence of human residence strategies p. 12 1.2.1 Resources p. 12 1.2.2 Productivity p. 14 1.2.3 Warfare p. 14 1.2.4 Individual investment in offspring versus kin p. 16 1.2.5 Inter- and intra-generational conflict within the family p. 18 1.3 Dispersal, life history traits and cooperative breeding p. 20 1.4 Foreword to a model of dispersal p. 22 CHAPTER II p. 24 Summary p. 24 2.1 Methods p. 24 2.1.1 AGENT-BASED MODEL p. 24 2.1.2 EXPERIMENTS p. 30 2.2 Results p. 33 2.3 Discussion p. 38 2.4 Conclusion p. 40 2.5 Supplementary Information: cultural mutation p. 41 CHAPTER III p. 43 3.1 The Mosuo p. 43 3.1.1 Human behavioural ecology of the Mosuo p. 45 3.2 The Han p. 47 3.3 Male investment towards household subsistence: a history of conflict p. 48 CHAPTER IV p. 52 4.1 Methods p. 52 4.2 Results p. 59 4.3 Discussion p. 64 2 4.4 Conclusion p. 66 CHAPTER V p. 67 5.2 A general discussion p. 67 5.2 Conclusion p. 70 References p. 71 Appendix 1 p. 75 Appendix 2 p. 90 Final word count: 22,982 Final word count with references and appendices: 31,943 3 List of tables Table 1.1: PMRS key terminology p. 10 Table 2.1: Strategy classification based on dispersal decisions made by couple’s members p. 28 Table 4.1.1: Descriptive statistics of collected data for the response and each predictor variable used p. 55 Table 4.1.2: Summary of data for categorical variables in the used predictor subset (marriage status and partner co-residence status) p. 57 Table 4.1.3: List of predictors of total number of hours worked for each analysed data set p. 58 Table 4.2.1: Effect size and summed weight of tested predictors of total hours worked for the full data-set. p. 60 Table 4.2.2: Effect size and summed weight of tested predictors of total hours worked for the Mosuo data-set. p. 61 Table 4.2.3: Effect size and summed weight of tested predictors of total hours worked for the Han data-set. p. 61 Table 4.2.4: Effect size and summed weight of tested predictors of total hours worked for the female Mosuo data-set. p. 62 Table 4.2.5: Effect size and summed weight of tested predictors of total hours worked for the male Mosuo data-set. p. 62 Table 4.2.6: Effect size and summed weight of tested predictors of total hours worked for the married male Mosuo data-set. p. 63 Appendix table 1: Collected household data for each individual participant. p. 90 Appendix table 2: Data on worked hours by individual participants p. 97 4 List of figures Figure 2.1.1: Flowchart of the model, from the agent’s perspective p. 31 Figure 2.1.2: Flowchart of the model, from a household perspective p. 32 Figure 2.2.1: Trajectories over time of the population-average sex-specific dispersal trait values and relative PMRS frequencies, in the full life-history model p. 33 Figure 2.2.2: Boxplots showing variability in final dispersal trait values and PMRS frequencies in the full life-history model. p. 34 Figure 2.2.3: Trajectories over time of the population-average sex-specific dispersal trait values and relative PMRS frequencies, in the basic model p. 36 Figure 2.2.4: Representative trajectories of population average dispersal traits under the female- biased cost and variability plots of the final trait values and PMRS frequencies, when duolocality is absent p. 37 Supplementary Figure 2.5.1: Trajectories of the mean population dispersal trait values and PMRS frequencies shown under both cost conditions in the mutation model p. 41 Figure 3.1: Map of the fieldwork site, Lugu Lake, within the People’s Republic of China p. 43 Figure 4.1.1. Bar graph showing number of individuals in each age category in the collected data, divided by sex and ethnicity. p. 57 5 Abstract This thesis was presented at the University of Manchester by Edith Invernizzi, candidate for the degree level Master of Philosophy in Bioarchaeology, in date 27th September 2016, with the title The evolution of human post-marital residence. Post-marital residence is an aspect of human cultures strongly connected to ecology. It influences the dynamics of fitness conflict within the family nucleus, but it also interacts with environment’s ecology through its dependence on resources. The problem of why this trait should take different forms within the same species has been the subject of a longstanding debate. Here, I will present a theoretical simulation study modelling the emergence of post-marital residence strategies (PMRS), whose results show how reproductive cost and offspring investment are drivers of sex-biased dispersal. The mechanism described represents an underlying factor to strategy evolution, in-built in human life-history, with which other ecological aspects are likely to interact. This outcome places the two factors mentioned at the centre of the discussion on strategy emergence. To attempt an empirical investigation of sex differences in offspring investment, I will present a fieldwork study conducted among a Chinese ethnic minority, the Mosuo, in which members of a married couple reside separately, each with their matrilineal kin. This study consists in a series of exploratory analyses of labour effort allocation and is aimed at addressing the problem of male contribution to household subsistence (here seen as a form of family investment). My perspective, as formed from the results, is of the emergence of different strategies as (also) resulting from the unstable balances reached in the conflict for reproductive investment between the sexes. 6 Declaration The candidate Edith Invernizzi hereby declares that portions of Chapter I in the present thesis have been submitted as part of a literature review for the present degree course in December 2015, under the title “Agent-based modelling and the evolution of residence strategies”. No other portion of the work used or referred to in the following thesis has previously been submitted in support of an application for another degree or qualification of this or any other university or other institute of learning. Copyright statement i. The author of this thesis (including any appendices and/or schedules to this thesis) owns certain copyright or related rights in it (the “Copyright”) and she has given The University of Manchester certain rights to use such Copyright, including for administrative purposes. ii. Copies of this thesis, either in full or in extracts and whether in hard or electronic copy, may be made only in accordance with the Copyright, Designs and Patents Act 1988 (as amended) and regulations issued under it or, where appropriate, in accordance with licensing agreements which the University has from time to time. This page must form part of any such copies made. iii. The ownership of certain Copyright, patents, designs, trade marks and other intellectual property (the “Intellectual Property”) and any reproductions of copyright works in the thesis, for example graphs and tables (“Reproductions”), which may be described in this thesis, may not be owned by the author and may be owned by third parties. Such Intellectual Property and Reproductions cannot and must not be made available for use without the prior written permission of the owner(s) of the relevant Intellectual Property and/or Reproductions. iv. Further information on the conditions under which disclosure, publication and commercialisation of this thesis, the Copyright and any Intellectual Property University IP Policy (see http://documents.manchester.ac.uk/display.aspx?DocID=24420), in any relevant Thesis restriction declarations deposited in the University Library, The University Library’s regulations (see http://www.library.manchester.ac.uk/about/regulations/) and in The University’s policy on Presentation of Theses 7 Acknowledgments This Master of Philosophy was made possible only by the generous contribution of Mr James Davidson to the KNH Centre for Egyptology, University of Manchester. I thank Prof Andrew Chamberlain for taking the risk of awarding me the funding. The project and research work was created and put into effect only thanks to the collaboration of the Human Evolutionary Ecology research group at the University College of London (UCL) and of the Zoology department at the Chinese Academy of Sciences (CAS), Beijing branch. I thank in particular: Prof Ruth Mace (UCL) Prof Yi Tao (CAS) Dr Ji Ting (UCL and CAS) Dr Qiaoqiao He (CAS) Dr Matthew Thomas (UCL, Norwegian Institute for Cultural Heritage Research (NIKU) and Norwegian Institute for Nature Research (NINA)) I thank Prof Andrew Chamberlain and Dr Tucker Gilman for the excellent supervision and personal support. 8 CHAPTER I Introduction Human dispersal in relation to mating shows considerable within-species variation in its sex bias. When looking at the movement of the two members of a couple after marriage, opposite PMRSs such as patrilocality and matrilocality are found in populations living in relatively close geographical proximity.