The Search for a Rigorous, Generally Applicable Formulation of Inclusive Fitness Theory

Abstract

Since its introduction in the 1960s, inclusive fitness theory and its results, especially Hamilton’s rule, have been the topic of unresolved and ongoing debate. Over the past decade, arguments have increased in intensity following an outspoken critique by Nowak et al. in 2010. Opponents claim that general applications of the theory result in complex relationships between the quantities it describes, giving no real insights into how social behaviours may be positively selected; but specific applications are limited in scope, making it difficult to compare between cases. This project looks to assess to what extent generality of Hamilton’s rule comes at a detriment to its causal descriptive power. To assess this, I first describe the various forms that the parameters of cost, benefit and relatedness in Hamilton’s rule may take, and assess their theoretical limitations in each case. I then consider how Hamilton’s rule may be applied to a computational simulation model where all details of the system may be known, provide rigorous definitions of parameters that may be applied to an empirical study, and demonstrate what restrictions apply. Finally, I analyse previous results that utilised Hamilton’s rule to interpret experimental data, examining to what extent predictions between experiments using inclusive fitness theory may be unified. It is shown that while there is a wealth of empirical data indicating that altruism can evolve if it increases an individual’s ‘inclusive fitness’, how this fitness is defined subtly differs from case to case, with no clear path to link these results to each other. Despite the value in these experimental results, further work must be taken in order to unify predictions made by Hamilton’s rule before it can be considered a fully general method usable to interpret the conditions for the evolution of altruism. Nevertheless, it remains the most general method known for understanding the evolution of altruism thus far.