The arguments of Bill Eberhard (1996) and Patty Gowaty (2004) suggest that female control of fertilization may represent a form of mate choice.At present, a popular hypothesis is that multiple factors may be at work to set the stage for sexual selection (see Shuster and Wade 2003).
Over the last 130 years, research has established that (a) sexual selection exists and is widespread in the plant and animal kingdoms; (b) it does not necessarily entail sexual dimorphism; even hermaphrodites have it; (c) it does not require intelligence or a sophisticated sense of esthetics; even tapeworms and plants choose mates; and (d) it does not require brawn or even mobility for competition; plants may compete for pollinators, and broadcast spawning invertebrates may also compete for matings.
Although discussions of sexual selection often focus on sexual dimorphism, several phenomena that are commonly associated with sexual selection are widespread and highly developed in hermaphrodites.
Much of sexual selection research still focuses on sexual dimorphism (for example, Shuster and Wade 2003) and sexual dimorphism and secondary sexual characters are often used as proxies for evidence of sexual selection (see Table 1; Shuster and Wade 2003; Jones and others 2004; Kappeler and Van Schaik 2004; Mead and Arnold 2004; see discussion in Andersson 1994) and/or as part of the definition of sexual selection (Table 1).
The first questions to address, then, are the nature of sexual selection and how it might apply to hermaphrodites.
Table 2 lists factors that have been considered to be important in determining the strength and direction of sexual selection by producing differences between the sexes (or sexual roles) in variance in reproductive success and consequently skewed breeding sex ratio (BSR).