The costs and benefits of re-defining sexual selection: a comment on Shuker and Kvarnemo

In their thoughtful, clearly argued and comprehensive review of definitions of sexual selection, Shuker and Kvarnemo make a strong case for defining sexual selection as operating through access to gametes (Shuker and Kvarnemo 2021). This differs from some previous definitions of sexual selection which additionally include selection operating between females or males arising from intrasexual competition for breeding opportunities or the suppression of rivals (Darwin 1871; Clutton-Brock 2007; Watson and Simmons 2010) or from intrasexual competition for access to breeding partners that contribute to the care of offspring in situations where access to the gametes of the opposite sex is unlikely to limit the breeding success of individuals (Andersson 1994, Reynolds and Szekely 1997). For example, Andersson’s widely used definition of sexual selection includes intrasexual competition between females to monopolize access to males in polyandrous birds where the benefit of having access to multiple partners probably lies in their additional contributions to parental care rather than in access to additional gametes (Reynolds and Szekely 1997; Emlen and Wrege 2004). In contrast, Shuker and Kvarnemo would presumably regard this as a form of natural selection.