Why Sex? A Pluralist Approach Revisited

Why sexual reproduction predominates in nature remains a mystery. The mystery stems in part from the fact that many of the plausible hypotheses for sex have restrictive assumptions. Two decades ago these limitations inspired the formulation of a ‘pluralist’ approach in which standalone hypotheses for sex were considered together. Here we review representative literature to address whether this strategy has deepened our understanding of sex. We found surprisingly few papers adopting such an approach, probably reflecting challenges associated with testing multiple mechanisms. Nevertheless, these studies provided new insights, highlighting in particular the potential importance of interaction between parasites and harmful mutations. We conclude with strategies for moving forward, including broader formulations of pluralism and the application of more qualitative types of testing. Why sexual reproduction is so common is the ‘queen of problems’ in evolutionary biology. Pluralist hypotheses that combine multiple mechanisms can in theory counter the major limitations characterizing many if not all standalone hypotheses for sex. We address whether these theoretical expectations are supported by empirical studies. Only a few directly relevant studies exist, but most have positive outcomes and provide new directions. In particular, these study outcomes emphasize the value of a flexible, more qualitative approach to pluralism and the combination of key genetic and ecological factors. We provide empirically focused suggestions for future studies.