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Sexualities, Evolution & 6.1 April 2004 pp. 3–13

Sex differences in strategies: Mate guarding, and multiple concurrent partners

Susan M. Hughes*, Marissa A. Harrison and Gordon G. Gallup Jr State University of New York at Albany, USA ......

Abstract We investigated sex differences in post-copulatory mate guarding behaviors, jealous reactions to opposite- versus same-sex infidelity, and preferences for multiple concurrent sex partners. Results of a questionnaire administered to 448 college students showed that: (1) were more likely to initiate the practice of sleeping with their partner after ; (2) males were more distressed by opposite-sex infidelity, whereas females were equally distressed by both opposite- and same-sex infidelity; and (3) males were more willing than females to engage in sex with multiple concurrent partners. Under hypothetical conditions, males preferred having concurrent sex with two partners, while females showed a more varied preference for the of the other participants. These findings are consistent with predictions derived from evolutionary theory based upon sex differences in genetic assurance, and reproductive potential.

Keywords: , infidelity, , sex differences, mate guarding

*Now at Vasser College, USA

Sexualities, Evolution & Gender ISSN 1479–2508 print/ISSN 1470–1073 online ß 2004 Taylor & Francis Ltd http://www.tandf.co.uk/journals DOI: 10.1080/14616660410001733588 4 Susan M. Hughes et al.

Introduction Sex differences in mating strategies emerge from several fundamental biological differences between the sexes (Symons 1979). As a result of , maternity in is certain, whereas paternity is not. For a male, there is always the risk that he might invest in not biologically his own. Second, since there are profound differences in parental investment with females bearing the brunt of , childbirth and child rearing, abandonment of the female by her mate would lead to deprivation of paternal resources and care that is important for offspring survival (Gallup and Suarez 1983). Another important difference between males and females is production. Males produce millions of expendable on a daily basis and have the capacity to impregnate many females. Conversely, are scarce, and females have fewer opportunities to produce offspring. This sex difference in reproductive potential leads to vast differences in fitness strategies. For males, multiple mates confer a large reproductive advantage. For females, the largest advantage would be to form a relationship with a male who has ample resources and is will- ing to make a long-term commitment to provisioning and protecting the female and her offspring, while having short-term mates of high genetic quality. Differences in are consistent with this analysis. For instance, male sexual jealousy functions to guard a mate and to dissuade sexual competitors, thereby lowering the likelihood of by a rival mate (Daly, Wilson and Weghorst 1982). A female, on the other hand, has to contend with the possibility that her mate could abandon both her and her offspring, depriving necessary resources. Thus, rather than an anti-cuckoldry strategy, female sexual jealousy is an to the threat of abandonment. In the current study we attempted to examine the following three hypotheses regarding sex differences in .

Post-copulatory mate guarding behavior There is a widespread tendency for people who are in a to sleep with one another after they have had sexual intercourse. Since humans tend to be nocturnal copulators (Ford and Beach 1951), one would expect the highest risk of infidelity to also be at night. If sleeping together is initiated by males, it could function as an anti-cuckoldry strategy, whereby the male guards his mate to Mating strategies 5 minimize access by other males. On the other hand, if sleeping together is prompted by females, it could be thought of as an anti-philandering strategy that may minimize abandonment. While sleeping together after affords benefits for both sexes, we hypothesize that sleeping with a mate is more advantageous for females than for males. Sleeping with a mate may also offer the female protection from other males and protection from the possibility of an unwanted forced copulation. Furthermore, if a female remains in a horizontal position after copulation, this may aid in the retention of sperm and therefore increase the likelihood of conception (see Gallup and Suarez 1983).

Reactions to opposite- and same-sex infidelity Research has shown that men are especially bothered by evidence of their mate’s sexual infidelity, while women are troubled by evidence of emotional infidelity (Buss, Larsen, Westen and Semmelroth 1992). Whereas female sexual infidelity raises the prospect of cuckoldry (by duping the male to invest in offspring not biologically his own), male emotional infidelity signals the potential loss of investment and commitment to the female. Since men are disturbed by the prospect of female sexual infidelity, we predict males would become upset if their partner had sexual with other men but not other women, since an extra-pair male but not a female could impregnate their mate. In other words, sex between two women does not reduce paternity confidence, and therefore is not threatening to reproductive fitness. We predict that women, on the other hand, will be distressed by both same- and opposite-sex acts of infidelity, because in either case there is a potential for the diversion of resources and abandonment. Few studies have focused on sexual jealousy as a function of the gender of the interloper. Weiderman and LaMar (1998) found that female– female sexual infidelity is considered the least upsetting by both sexes. They also showed that men found male–female sexual infidelity most upsetting, whereas women found male–male sexual infidelity most upsetting. In contrast, Sagarin, Becker, Guadagno, Nicastle and Millevoi (2003) found that both males and females are more disturbed by opposite-sex infidelity than by same-sex infidelity. We believe these discrepancies may exist because females find male–male sexual infidelity as upsetting as male–female sexual infidelity; since both instances raise the specter of abandonment. 6 Susan M. Hughes et al.

Sex differences in preferences for the sex of multiple concurrent partners We expect males to report a desire to participate in multiple-female sexual situations such as ‘’ or . Since sperm are plentiful, males have the capacity to many offspring. Although short-term mating may have negative consequences for a male (i.e., reputation damage, physical retribution from her male partner or father, disease, etc.), males are largely exempt from having to contend with the reproductive consequences of sex (e.g., pregnancy, feeding, etc.). Therefore, males can maximize their fitness by copulating with many females (Gallup and Suarez 1983). Previous research has shown that men have a greater preference for and fantasize about group sex more than women, and this difference persists across all ages that were examined (Wilson 1997). It was concluded that this difference directly reflects the genetic advantage gained by polygynous males over millennia of evolution. We examined sex differences in the willingness to engage in a threesome and anticipated that males would be more likely than females to mate with multiple concurrent opposite-sex partners. Females, on the other hand, do not realize as much of a reproductive advant- age by copulating with multiple concurrent sex partners. A female can only be impregnated by one male, and group sex is not conducive to the development of a long-term committed relationship with a mate who will provision and support the female and her offspring. Hence, we predicted that females should not be as willing as males to engage in a threesome, nor be as particular about the sex of the other participants. These hypotheses were evaluated by surveying attitudes toward: (1) post-copulatory mate guarding behaviors; (2) hypothetical responses to same- versus opposite-sex acts of infidelity; and (3) multiple concurrent partner sexual encounters.

Methods A questionnaire approved by the local Institutional Review Board was administered to 448 undergraduate students (255 females and 193 males) in various psychology classes at the University at Albany, State University of New York, USA. The mean age of the participants was 21.02 (SD ¼ 3.2), with ages ranging from 18 to 47. Only participants Mating strategies 7 who reported being heterosexual were included for analysis, yielding a sample of 243 females and 185 males. Participants were solicited through an announcement made by the investigators at the end of class period. Completion of the questionnaires was voluntary, and students were not offered any course credit or compensation for their participation. Participants completed the questionnaire independently and privately to ensure that their responses were anonymous. Participants were asked demographic information regarding their and marital/relationship status. The instrument contained questions concerning infidelity, post-copulatory sleeping patterns, reactions to the sex of an interloper in an act of partner infidelity and attitudes concerning hypothetical participation in sex with multiple concurrent partners.

Results

Post-copulatory mate guarding behavior Participants were asked how important it is to spend the night sleeping with/ to their partner after a sexual encounter using a four-point Likert scale (1 ¼ it is unnecessary, 0 ¼ no preference, 1 ¼ of some importance, 2 ¼ very important). An independent t-test showed that females (mean ¼ 1.30, SD¼0.80) felt that sleeping together was more important than males (mean ¼ 0.94, SD ¼ 0.93), t(425) ¼4.298, p<0.00. These results were not affected by whether the participants were currently involved a sexual relationship. Participants were also asked who initiates sleeping together after having sex. A chi-square revealed a significant difference, ( 2 [3, n ¼ 427] ¼ 586.96, p<0.000), with 73.7% of all respondents indicating that females are more likely than males to initiate sleeping with their partner after sex (see Figure 1).

Reactions to opposite- and same-sex infidelity Participants were asked, ‘If I found out my / was cheating on me, it would disturb me more if the other party involved was (which sex)?’ Responses were: (a) opposite sex of my partner; (b) same sex of my partner; (c) equally disturbed if it were a same- or opposite-sex ; or (d) I would not be disturbed if my partner had an affair. As shown in Figure 2, there was a significant sex difference with 62% of males being more disturbed if the affair involved the 8 Susan M. Hughes et al.

100

80

60

Percent 40

20 gender

male

female 0

Males Females Both sexes Does not matter to either sex

Who initiates sleeping together? Figure 1 Which sex initiates sleeping together after sexual intercourse?

80

60

40

20 Percent Showing Jealousy gender

male

0 female Opposite Same Equally disturbed Sex of extra-pair interloper Figure 2 Sex differences in jealousy concerning infidelity. Mating strategies 9 opposite sex of their partner, while 70% of females were equally disturbed if it were a same- or opposite-sex affair ( 2 [3, n ¼ 428] ¼ 138.345, p<0.000).

Sex differences in preferences for the sex of concurrent multiple partners In response to the question ‘Would you ever engage in a threesome sexual situation?’ there was a significant sex difference ( 2 [1, n ¼ 428] ¼ 90.145, p<0.000). Over twice as many males (78%) than females (32%) reported that they would engage in concurrent sex with two other people. Participants were also asked what their preference would be for the sex(es) of the other partners. The choices were: (a) two males and myself; (b) two females and myself; (c) a male, a female and myself; and (d) the gender of the two other participants would not matter. There was a significant sex difference in preferences for the sex of the other partners ( 2 [3, n ¼ 403] ¼ 349.625, p<0.000). Among males, 97% expressed a preference for engaging in sex with two females, whereas females showed a more varied preference for the gender of the other participants: 53% preferred two males; 4% preferred two females; 27% preferred a male and a female; and 16% indicated that the sex of the other participants did not matter (see Figure 3).

100

80

60 Percent

40

gender 20 male

0 female

two males two females a male and gender of others a female does not matter Preference for sex of concurrent sex partners

Figure 3 Sex differences in preferences for the sex of participants in a ‘threesome’ sexual situation. 10 Susan M. Hughes et al.

Discussion This study provides further evidence that human mating preferences have been shaped by an evolutionary history that featured sex differ- ences in reproductive strategies. From the standpoint of sleeping together, females rated sleeping with their partner following sex as more important. In addition, both sexes indicated that females are usually the ones to initiate sleeping together. In our view, sleep- ing together functions as a mate-guarding tactic. The fact that sleeping together is often female-initiated suggests that it may be used as an anti-philandering strategy to minimize abandonment. It is also possible that females use sleeping together to accommodate and minimize male suspicions of cuckoldry. That is, a female who remains in close proximity to her mate after retiring at night may reassure her fidelity. By promoting greater paternity confidence, this, in turn, would increase the likelihood that the male will provision and care for her and her offspring. Sleeping together may also aid and abet conception. There is reason to believe that remaining in a horizontal position for an extended period of time after copulation may facilitate sperm retention and transport (Gallup and Suarez 1983). Sleeping with her mate might also provide protection from predators and unwanted sexual advances from other males. Our results show that males were more disturbed by the prospect of their partner having an affair with a member of the opposite sex. A rival male could potentially impregnate the female and result in cuckoldry. In contrast, a female–female sexual pairing poses no threat to paternity. For a female, however, an affair on the part of her mate poses the threat of abandonment, regardless of the rival’s sex. Sagarin et al. (2003) argued that females are distressed more by opposite-sex acts of infidelity due to the possible diversion of resources to the children of a rival female. However, we found that female concern was independent of the rival’s risk of conception. Both same- and opposite-sex acts of infidelity can lead to abandonment and have the potential to divert resources and attention. Moreover, if distress were dependent on the interloper’s potential for , jealousy due to infidelity among lesbians and men would not be expected. There are, however, many accounts of homosexual sexual and emotional jealousy due to infidelity (Buunk and Dijkstra 2001). It would appear that jealousy is not tied to conscious knowledge about reproduction, but rather the threat of sexual infidelity. It is important to note that these sex differences in reactions to same- and opposite-sex infidelity persist after controlling for religiosity, Mating strategies 11 sex- association beliefs, erotophobia/erotophilia, erotization of same-gender sexual contact and attitudes towards one’s partner having same-gender sexual contact (Weiderman and LaMar 1998). Thus, responses to jealousy-invoking stimuli such as the gender of the interloper seem to be primarily a manifestation of evolved psychological mechanisms rather than social, personality and cultural constructs. In terms of the prospect of having sex with multiple concurrent partners, our data show that males were much more willing than females to participate in a threesome. Whereas males expressed a preference for having sex with two females, female preference for the sex of the other participants was more varied. These results are consistent with other findings regarding sex differences in attitudes concerning group sex. Wilson (1987) found that men were about twice as likely as women to report fantasies and/or enjoyment of group sex. In addition, the majority of threesomes involve two women and one man. Data derived from reports of those who have engaged in threesomes show that female–female contact seems to be less threatening to women than does male–male contact (Karlen 1988). Furthermore, females are more likely to fantasize about same-sex partners than men (Wilson 1997). However, the relative unwillingness of women to take part in sex with multiple concurrent partners may be driven by the effect that participation would have on her reputation, particularly since in women predicts infidelity (Hughes and Gallup 2003). When it comes to multiple sexual partners, a threesome with two females could be reproductively beneficial for a male since it would increase the chances of producing offspring. Females, on the other hand, have less to gain by copulating with multiple concurrent partners. It only takes one male to impregnate a female, and impregnation followed by reduces the likelihood of re-impregnation for a period of several years. The benefits of multiple mating by females include , , protection and obtaining fertile sperm when with an infertile partner (see Baker and Bellis 1993; Bellis and Baker 1990; Thornhill, Gangestad and Comer 1996). Recent evidence shows that independent ratings of attractiveness predict sperm quality (Soler, Nunez, Gutierrez, Nunez, Medina, Sancho, Alvarez and Nunez 2003) and longevity (Henderson and Anglin 2003), which are heritable traits that may provide leverage for impregnation as a byproduct of sperm competition. Cultural attitudes toward and group sex also tend to map onto evolutionary theory. Negative connotations are 12 Susan M. Hughes et al. frequently ascribed to male–male sexual contact compared to female– female sexual activity. Nyberg and Alston (1977) found that only 7% of both men and women found ‘men making love to men’ to be erotic. In contrast, over three times as many men than women considered ‘women making love to women’ to be erotic. Accordingly, among married couples who engage in group sex, male–male contact is relatively rare, yet women are frequently encouraged to engage in female–female sexual activity by their (Dixon 1984). Eliason (1997) found that men were more willing to have a sexual relationship with a bisexual than women were to have a sexual relationship with a bisexual man. Some male respondents noted that having sex with bisexual women might increase the likelihood of having a threesome with the bisexual women’s female partner. In conclusion, our findings show sex differences in post-copulatory mate guarding behavior, reactions to same- versus opposite-sex infidelity and preferences for multiple concurrent sex partners. These differences are consistent with sex-specific psychological and biological mechanisms that may have evolved to drive reproductive fitness.

Address for correspondence Gordon G. Gallup Jr, Department of Psychology, University at Albany, State University of New York, Albany, NY 12222, USA. Tel.: (518) 442-4852, Fax: (518) 442-4687, E-mail: [email protected]

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