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Life History Theory and the Social Clustering of Adolescent Behaviour

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Life History Theory and the Social Clustering of Adolescent Behaviour Life history theory and the social clustering of adolescent behaviour Abram Joachim van Leeuwen Thesis presented for the degree of Doctor of Philosophy University College London 1 I, Abram Joachim van Leeuwen, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Abram J. van Leeuwen 2 Abstract Humans – foragers and megacity dwellers alike – inhabit complex social worlds. Many behavioural and non-behavioural traits show distinct patterns of social clustering: members of social groupings are more similar to each other than to random individuals. This thesis uses social clustering as an entry point for the study of behavioural variation, exploiting the fact that different causal mechanisms will produce different clustering patterns. I combine this with a focus on evolutionary explanations of behavioural variation, particularly those derived from life history theory, and apply this approach to contemporary adolescents in the United Kingdom. Adolescents are a key demographic from a life history theoretical perspective: transitioning from the pre- reproductive to the reproductive phase of life, adolescents start displaying many of the behaviours and traits of interest to life history theorists. Moreover, paths taken during adolescence may have long-term implications for an individual’s life history trajectory. I quantify social clustering of sexual experience and cooperativeness in neighbourhoods, schools and friendship networks and investigate whether life history predictors, such as socioeconomic deprivation and father absence, explain behavioural variation or their social clustering. I further examine the social clustering patterns across a range of behavioural and non-behavioural traits, in order to assess the explanatory scope of different evolutionary models. Finally, I examine whether measures of the quality of the childhood environment affect a range of measures of pubertal development in girls and boys, in line with theoretical predictions. Overall, results indicate that adolescent behaviours tend to cluster in friendship networks but barely in neighbourhoods or schools. This suggests limited scope for explanatory theories centred on contextual influences on behaviour in this population. While life history predictors do not explain much social clustering of adolescent behaviour, they are associated with sexual experience, cooperativeness, and pubertal development in ways broadly consistent with life history theoretical predictions. 3 Table of Contents Abstract .............................................................................................................................................................. 3 List of tables ................................................................................................................................................... 12 List of figures ................................................................................................................................................. 18 Acknowledgments ....................................................................................................................................... 20 Chapter 1: Introduction and background ........................................................................................... 21 1.1 Introduction ............................................................................................................................................ 21 1.2 Adolescence: an evolutionary theoretical perspective .......................................................... 24 1.2.1 What is adolescence? ................................................................................................................... 24 1.2.1.1 Social adolescence ................................................................................................................ 24 1.2.1.2 Biological adolescence ........................................................................................................ 25 1.2.1.3 Human adolescence in a comparative perspective ................................................. 27 1.2.2 The evolutionary function of adolescence .......................................................................... 27 1.2.3 Evolution and sex differences .................................................................................................. 29 1.2.3.1 Evolved sex differences stem from asymmetries in parental investment...... 29 1.2.3.2 Female and male reproductive strategies ................................................................... 29 1.2.3.3 Implications for adolescent behaviour ......................................................................... 31 1.2.4 Changes of adolescence in the light of evolution .............................................................. 33 1.2.4.1 Puberty leads to (biological) sexual maturity ........................................................... 33 1.2.4.2 Puberty rites ........................................................................................................................... 33 1.2.4.3 Emotional distancing from parents, turn towards peers ...................................... 34 1.2.4.4 Appearance of sex drive and romantic feelings ........................................................ 34 1.2.4.5 Intrasexual competition ..................................................................................................... 34 1.2.4.6 Possible functional significance of ordering .............................................................. 35 1.2.5 Some unusual features of adolescence in modern Britain ........................................... 36 1.2.6 Why adolescents are interesting to life history theorists ............................................. 37 1.2.6.1 Many behaviours of interest arise first during adolescence ................................ 37 1.2.6.2 Decisions made and paths taken during adolescence have downstream effects ....................................................................................................................................................... 38 1.3 Life history theory ................................................................................................................................ 39 1.3.1 General theory ............................................................................................................................... 39 1.3.1.1 Resource allocation and inclusive fitness.................................................................... 39 1.3.1.2 Trade-offs ................................................................................................................................. 39 1.3.1.3 The fast-slow continuum; two axes of co-variation of life history traits ........ 40 1.3.2 Human life histories..................................................................................................................... 42 1.3.2.1 The human life history in comparative perspective ............................................... 42 4 1.3.2.2 Adaptive life history variation in humans ................................................................... 42 1.3.3 Evolutionary models of adolescent development ............................................................ 43 1.3.3.1 Paternal investment theory .............................................................................................. 44 1.3.3.2 Psychosocial acceleration theory ................................................................................... 45 1.3.3.3 Child development theory ................................................................................................. 46 1.3.3.4 Intergenerational conflicts about reproductive opportunities ........................... 47 1.3.3.5 Early life adversity as an internal predictive adaptive response ....................... 47 1.3.3.6 Other models .......................................................................................................................... 48 1.3.4 Evolution and the Big Five personality factors ................................................................. 48 1.4 Predictions derived from an evolutionary perspective on adolescence and life history theory ................................................................................................................................................ 51 1.4.1 Predictions for chapter 3: experience with sexual intercourse .................................. 51 1.4.2 Predictions for chapter 4: cooperation ................................................................................ 53 1.4.3 Predictions for chapter 5: sex differences in substance use and personality traits ......................................................................................................................................................................... 54 1.4.4 Predictions for chapter 6 (pubertal development) ......................................................... 55 1.5 Social clustering .................................................................................................................................... 56 1.5.1 Examples of social clustering: adolescent substance use and sexual behaviour . 56 1.5.1.1 Clustering in social networks ........................................................................................... 57 1.5.1.2 Clustering in neighbourhoods ........................................................................................
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