The definition of sexual selection

Abstract

Sexual selection is a key component of evolutionary biology. However, from the very formulation of sexual selection by Darwin, the nature and extent of sexual selection have been controversial. Recently, such controversy has led back to the fundamental question of just what sexual selection is. This has included how we incorporate female-female reproductive competition into sexual or natural selection. In this review, we do four things. First, we examine what we want a definition to do. Second, we define sexual selection: sexual selection is any selection that arises from fitness differences associated with nonrandom success in the competition for access to gametes for fertilization. An important outcome of this is that as mates often also offer access to resources, when those resources are the targets of the competition, rather than their gametes, the process should be considered natural rather than sexual selection. We believe this definition encapsulates both much of Darwin’s original thinking about sexual selection, and much of how contemporary biologists use the concept of sexual selection. Third, we address alternative definitions, focusing in some detail on the role of female reproductive competition. Fourth, we challenge our definition with a number of scenarios, for instance where natural and sexual selection may align (as in some forms of endurance rivalry), or where differential allocation means teasing apart how fecundity and access to gametes influence fitness. In conclusion, we emphasize that whilst the ecological realities of sexual selection are likely to be complex, the definition of sexual selection is rather simple.

Substantial but Misunderstood Human Sexual Dimorphism Results Mainly From Sexual Selection on Males and Natural Selection on Females

“…Recently, Shuker and Kvarnemo (2021) have attempted to redefine sexual selection as “any selection that arises from fitness differences associated with non-random success in the competition for access to gametes for fertilization” (p. 783). We dislike this formulation because (as explained below) gametes are not always the limiting factor precipitating mating competition, and hence a definition based on them will yield somewhat paradoxical conclusions.…”

“…Matching the predictions of Clutton-Brock and Vincent’s (1991) theory, in species where males are the slow sex (e.g., phalaropes), females have evolved to be larger, more brightly colored, and more active in courtship—traits typically associated with mating competition in males. Shuker and Kvarnemo’s (2021) definition would require us to recognize such traits as due to sexual selection when they help males acquire female mates (whose gametes are scarce), but as due to natural selection when they serve the same function for females seeking male mates (because male gametes are not the target of competition). Because that kind of conceptual cleavage seems discordant with Darwin’s original framing of sexual selection as favoring traits useful in mate acquisition, we adopt Andersson’s (1994) widely used definition: “Sexual selection is the differences in reproduction that arise from variation among individuals in traits that affect success in competition over mates and fertilizations” (p. 31).…”

The Evolution of Playfulness, Play and Play-Like Phenomena in Relation to Sexual Selection

“…Different mechanisms of Sexual Selection have been proposed (cf. Puts, 2010;Shuker and Kvarnemo, 2021). For instance, men may play sports more often because women prefer sportive men (Faurie et al, 2004), because sports work as behavioral armaments in intrasexual competition (Lombardo, 2012) or as displays for potential parents-in-law (Apostolou, 2017), besides other bio-socio-cultural functions.…”

Environmental Correlates of Sexual Signaling in the Heteroptera: A Prospective Study

“…While sexual selection may be quite simple in outline-namely the selection that arises from the competition for access to gametes [146]-the ways in which that competition can manifest itself are extraordinarily diverse, leading to the great diversity of sexual traits that we see [1,6,128]. However, the mechanisms of competition for mates do not act in isolation.…”