Orgasm as a post-copulatory display

Lloyd’s (2005) book, The Case of the Female Orgasm: Bias in the Science of Evolution, has generated debate in this Journal (Puts, 2006a, 2006b; Wallen, 2006) and elsewhere (Zuk, 2006). Although these authors disagree about whether female orgasm is likely to be an evolutionarily selected trait or a ‘‘byproduct’’ of male sexual response, there seems to be a general consensus that orgasm as a phenomenon requires further investigation before confident inferences about its likely origins and functions can be made. Although I, also, hold the position that the proximate and ultimate causes and consequences of orgasm are poorly understood, the present letter attempts to highlight several features of orgasm which are consistent with a Darwinian interpretation. In addition, I propose that orgasm exhibits characteristics that are best interpreted in the context of signaling theory (Maynard Smith & Harper, 2003). In this letter, my statements about human sexual response, including orgasm, rely upon perspectives and evidence presented in Masters and Johnson (1966), Dixson (1998), Morris, Jordan, and Breedlove (2004), Hyde (2005), and Komisaruk, Beyer-Flores, and Whipple (2006). As implied by Zuk (2006), I propose that a functional understanding of orgasm requires that female and male sexual responses be considered together since orgasm and other components of sexuality derive from reproductive activities. Although my treatment will only consider sex between a male and a female (‘‘heterosexual’’ sex), it is not inconsistent with my views to assume that the original procreative goal of sexual response, in particular, orgasm, might assume different functions (e.g., same-sex partner choice; masturbation; ‘‘paraphilias’’) as facultative derivations from the original motivation. Finally, although a large literature exists on the genetic and physiological control of sexual response, the present discussion is independent of any assumptions about the necessary or sufficient roles of endogenous or exogenous factors for the induction of orgasm in either males or females. A modern Darwinian perspective assumes that individuals behave in a self-interested manner to optimize ‘‘inclusive fitness,’’ a condition that may favor selfish, cooperative, altruistic, or spiteful traits (Trivers, 1972, 1985; see also Darwin, 1871). Sexually selected characteristics (e.g., prominent breasts and buttocks displayed by human females or exaggerated musculature in males) are thought to confer advantages in competition for mates and/or mate choice and are ubiquitous among mammals and other sexually reproducing organisms. A strong inference for sexual selection is also made when males and females are shown to differ for the same trait. For example, features of female and male orgasm differ, notably in the refractory period, suggesting that sexual selection has acted upon this behavioral trait differently as it is thought to have acted on other traits (morphological, psychological: Dixson, Dixson, Li, & Anderson, 2007; Gangestad, Simpson, Cousins, Garver-Apgar, & Christensen, 2004; Geary, 2006). A case might also be made that human orgasm is sexually selected since it is an extravagant or exaggerated, possibly ornamental, response, often accompanied by vocalizations which may be variously interpreted as aggressive (possibly directed at potential challengers or coercive to the partner) or paedomorphic (appeasing and possibly attractive to the partner in copula). Exaggerated traits may also perform conditionand/or situation-dependent informational functions by communicating a sender’s C. B. Jones (&) Department of Psychology, College of Basic and Applied Sciences, Fayetteville State University, 1200 Murchison Road, Fayetteville, NC 28301, USA e-mail: cbjones@uncfsu.edu