Inclusive Fitness and Hamilton’s Rule

This chapter evaluates the long and intimate association between the gene’s-eye view and the work of W.D. Hamilton. Hamilton’s key insight was that individual organisms can affect the transmission of their genes through personal reproductive success, as well as through the success of close relatives. Inclusive fitness provides a way to view this process from the perspective of individual organisms, but it can also be seen from a gene’s-eye view. Dawkins and others have repeatedly emphasized the formal equivalence of the two perspectives. Yet, this chapter shows there is an underappreciated tension between the two perspectives. It demonstrates how this tension is expressed in both the current kerfuffle over the value of inclusive fitness theory stemming from Martin Nowak and colleagues and in Alan Grafen’s ongoing Formal Darwinism Project. The chapter ends by discussing two recent attempts to resolve this tension.

Grafen’s Formal Darwinism, Adaptive Dynamics

A core Darwinian idea is that evolution will lead to well-adapted organisms, with phenotypes that maximize their fitness relative to the available alternatives. Grafen’s ‘formal Darwinism project’ attempts to make this idea precise, by explicitly linking the process of natural selection and the optimality of individuals’ phenotypes. Grafen’s analysis ties in closely with the unity-of-purpose constraint on agency, but does not amount to a general vindication of adaptationist assumptions. Under frequencydependence, the theory of adaptive dynamics shows that natural selection does not necessarily lead to phenotypes which maximize fitness conditional on their being fixed in the population. These results suggest that there is no theoretical principle to the effect that natural selection will tend to produce adaptation. The justification for agential thinking in biology must thus be empirical, not theoretical.