Sexual Orientation and Human Sexuality As Inclusive fitness
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S Sexual Orientation and Human not necessarily manifested by overt sexual behav- Sexuality ior, associated with self-identification of sexual orientation label, or aligned with affectional bond- Jaroslava Varella Valentova and Marco Antonio ing (love). Correa Varella Department of Experimental Psychology, Institute of Psychology, University of São Paulo, Cidade Introduction Universitária São Paulo, SP, Brazil The majority of males and females predominantly prefer opposite-sex sexual and/or romantic part- Synonyms ners. Such sexuality has been accepted as a stan- dard default, possibly because it is easier to see its Bisexuality; Heterosexuality; Homosexuality; biological/evolutionary relevance. Indeed, in sex- Same-sex sexuality; Sexual attraction; Sexual ually reproducing species, preference for and sex- minorities; Sexual preference ual activities with opposite-sex partners evolved as a mechanism for combining genomes through complementary gametes gaining genetic variabil- Definition ity and direct fitness. Thus, scholars have argued that homosexuality is an evolutionary puzzle Sexual orientation refers to a psychological mech- because it impedes the reproductive success of anism directing one’s sexuality towards individ- their owners. However, on the phylogenetic uals based on their apparent sex. Individuals form level, evolutionary fitness is more than direct fit- a continuum between extreme point of exclusive ness, and on the ontogenetic level, sexuality is heterosexuals, i.e., oriented exclusively towards more than fertile heterosexual penile-vaginal individuals of the opposite sex, and exclusive intercourse. Although direct reproduction is the homosexuals, i.e., oriented exclusively towards ultimate evolutionary force behind most sexual individuals of the same sex, with bisexuals being activities, sexuality in general gained many other similarly attracted to both sexes and other individ- proximate functions during its evolution, e.g., as a uals being attracted to both sexes in various social and pair bonding mechanism or means of degrees (e.g., predominantly heterosexual with resource acquisition. Such functions are interme- some potential to same-sex attraction). Sexual diate goals to achieve direct reproduction, e.g., by orientation refers more to attraction or desire means of survival and alliance formation and/or than behavior or identity, because orientation is indirect reproduction by helping kin, also known # Springer International Publishing AG 2016 T.K. Shackelford, V.A. Weekes-Shackelford (eds.), Encyclopedia of Evolutionary Psychological Science, DOI 10.1007/978-3-319-16999-6_3622-1 2 Sexual Orientation and Human Sexuality as inclusive fitness. Therefore, many forms of predominantly heterosexual, bisexual, predomi- sexuality, such as oral or anal sex, masturbation, nantly homosexual, etc.). Similarly, a severe clin- sexual preferences for different species, prefer- ical depression or severe forms of autism are most ences of same-sex individuals, or individuals out- probably not adaptive; they are not only neutral side of reproductive age, cannot per se offer direct but rather maladaptive. However, they both are reproductive success of the individual, but still extremes on a continuum of adaptive variation, these nonfertile forms of sexuality can offer such as the capacity of sadness and systemizing other adaptive sociosexual functions (e.g., pair abilities, respectively (for an overview about bonding, alliance formation, resource acquisition, adaptive individual differences see, Buss and well-being, etc.) that might indirectly foster future Greiling 1999). In the same line, bisexuality or reproduction, regardless of sexual orientation. It is some degree of homosexual tendencies among important to note that personal motivations for predominantly heterosexual individuals as well sexual activities, homosexual or heterosexual as some heterosexual tendencies among predom- ones, are quite different from their possible socio- inantly homosexual individuals could be viewed sexual functions or possible evolutionary adaptive as adaptive variation of sexual orientation. From values. Sexual relations are mostly motivated by this perspective, even if exclusive homosexuality pleasure, love, self-esteem/revenge, and/or does not have any possible adaptive value, it obtaining resources. Such personal motivations would be a mistake to assume that the same is triggering homo/heterosexual behavior should true for the whole continuum of sexual not be confused with the socioecological or evo- orientation. lutionary reasons that maintain sexual activity in the population. Further, sexual orientation is a psychological Evolutionary Theories of Sexual mechanism that generates a continuous array of Orientation individual variation and not a dichotomous psy- chological trait (e.g., Kinsey et al. 1948; Petterson Sexual orientation has been described as a mech- et al. 2015). In this sense, exclusive homosexual- anism navigating or directing sexuality towards ity and exclusive heterosexuality present the individuals of the opposite sex, same sex, or in extreme opposite poles of the continuum, while varying degrees to both sexes (Bailey 2009; Bai- the majority of individuals fall in between, ley et al. 2016; Savin-Williams 2016; Vrangalova although closer to the heterosexual extreme. Fol- and Savin-Williams 2012). Similar to some het- lowing this line, homosexuality or nonhetero- erosexual practices (e.g., extra-pair affairs), atti- sexuality (including bisexuals) is more than tudes toward same-sex sexuality can vary greatly exclusive homosexuality, and sexual orientation between cultures. In some cultures, same-sex sex- does not equal homosexuality. One possibility uality constitutes an integral part of the sociocul- would be to focus on the adaptive value of the tural system; in others such sexuality is mechanism itself (i.e., sexual orientation); the criminalized and persecuted (for review see, Bai- other would be to explore the possible adaptive ley et al. 2016). For these reasons, individuals can value of one of its manifestations (e.g., exclusive vary in their overt manifestation of sexual prefer- homosexuality). The adaptiveness of the mecha- ence, from a tendency hidden from public or even nism itself is usually not the focus of the debate. self to open preferences and behaviors. There are The debate is mostly centered on whether and also other motives why sexual preferences, behav- how the individual differences generated by this iors, and identities do not need to be aligned. mechanism are adaptive. A mistake would be to Nonpreferred sexual behavior can be manifested, extrapolate a possible nonadaptiveness of an for example, under conditions without access to extreme point within the continuum (exclusive preferred sexual partners; it can be done for finan- homosexuality) to the other variations along the cial motives or simply to satisfy one’s partner. whole continuum of sexual orientation (e.g., Similarly, romantic affection can be largely Sexual Orientation and Human Sexuality 3 disconnected from sexual desires (Diamond success of transgendered male homosexuals 2003). For example, a person can repeatedly fall (males who adopt female look and behavior) is in love only with individuals of the same sex, but close to zero (Vasey et al. 2014), this does not prefer and actively seek sexual partners of both need to apply to other forms of nonheterosexual sexes. Thus, sexual orientation refers to sexual individuals. In one study, 32.8 % of men and desires, attraction, and preferences rather than to 65.4 % of women reported a potential for homo- overt sexual behavior, identity, or affective sexual response, suggesting that a huge percent- feelings. age of predominantly heterosexual people do have Sexual orientation has a genetic component a propensity to experience same-sex sexual attrac- that explains approximately one third of the vari- tion and/or interaction (Santtila et al. 2008). In this ation between individuals (e.g., Zietsch study, the potential for homosexual response was et al. 2012; for review, see Bailey et al. 2016). based on responses (quite impossible, very This suggests that sexual orientation is a complex unlikely, quite unlikely, not likely, not unlikely, trait that is influenced by genetic and environmen- relatively likely, very likely) on the following tal factors. Sex hormones are one of the environ- question: “If a, in your opinion, handsome man mental factors that influence the development of [to male participants]/beautiful woman [to female sexual orientation. According to the organiza- participants], whom you like, suggested sexual tional hypothesis, the neural system of homosex- interaction with you, how likely would you be ual individuals is influenced by sex-atypical able to do it (if you could define the nature of the hormone levels during early developmental interaction and nobody else would know about phases. Systematic differences in neuroanatomy it)?”. In line with this finding, a large-scale study between homosexual and heterosexual individ- demonstrated that almost 10 % of heterosexually uals suggest that compared to their heterosexual identified men reported that they have engaged in counterparts homosexual men were, on average, same-sex sexual activities (Pathela et al. 2006). less androgenized and homosexual women more This applies even more to non-Western androgenized during early, probably prenatal, populations, such as Samoa, where the majority development (for review, see Bailey et al. 2016; of predominantly