Life history theory and the social clustering of adolescent behaviour
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 prereproductive 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.