On monism and pluralism: a reply to Dickins, T. E.

Dickins has made some thoughtful suggestions as to why the important contributions of inclusive fitness theory have not been more celebrated by the proponents of the Extended Evolutionary Synthesis, considering the extent to which inclusive fitness theory has accommodated and illuminated—and, indeed, been motivated by—their “laundry list” of supposedly neglected evolutionary factors. We agree that this oversight could be explained, in part, by their seeing inclusive fitness as a “monist” alternative to a more “pluralist” multilevel selection that was not part of the Modern Synthesis. Here we clarify that multilevel selection and inclusive fitness are not competing explanations, but rather they address orthogonal issues, concerning the process of selection and the purpose of adaptation, respectively. We discuss the sense in which inclusive fitness is “monist” in providing the only generally correct adaptive maximand, but also “pluralist” in the sense of accommodating a diversity of adaptive agents. We also emphasise that multilevel selection was, in fact, part of the Modern Synthesis and, indeed, its inadequacies as a theory of organismal adaptation provided a crucial motivation for the concept of inclusive fitness.