Merits and criticism of the regression-based formulation of inclusive fitness theory

Abstract

Hamilton’s rule and the theory of inclusive fitness have become a central part of the theory of social evolution. However, as is well known, the original formulation of this theory is strictly valid only when the fitness effects of the social trait are additive. Several attempts have been proposed to derive a version of inclusive fitness theory that also holds more generally. In particular, a version of Hamilton’s rule has been derived using the formalism of partial regression in combination with the Price Equation. It is sometimes claimed that this “general” Hamilton’s rule can be applied to any social trait and is “as general as the Price equation”. Other prominent voices have criticized the approach vocally. For instance, one criticism is that, since in the general version of Hamilton’s rule the costs and benefits are defined as regression coefficients, they do not necessarily represent causal effects. Another criticism is that this formalism cannot be used to make predictions. In this review, we evaluate some of the key arguments in favor of and against the general mathematical formulation of inclusive fitness theory. We con- clude that the Price equation is a powerful and versatile framework, but we express our concerns regarding the interpretability of the regression- based formulation of Hamilton’s rule. Finally, we share our own views on the debate and how it can be constructively advanced in the future.