Male androphilia, fraternal birth order, and female fecundity in Samoa: A 10-y retrospective.

Two separate but related literatures have examined familial correlates of male androphilia (i.e., sexual attraction and arousal to masculine adult males). The fraternal birth order effect (FBOE) is a widely established finding that each biological older brother a male has increased the probability of androphilia 20-35% above baseline rates. Other family demographic variables, such as reproduction by mothers, maternal aunts, and grandmothers, have been used to test evolutionary hypotheses that sexually antagonistic genes lead to androphilia among males, lowering or eliminating reproduction, which is offset by greater reproductive output among their female relatives. These proposed female fecundity effects (FFEs), and the FBOE, have historically been treated as separate yet complementary ways to understand the development and evolution of male androphilia. However, this approach ignores a vital confound within the data. The high overall reproductive output indicative of an FFE results in similar statistical patterns as the FBOE, wherein women with high reproductive output subsequently produce later-born androphilic sons. Thus, examination of the FBOE requires analytic approaches capable of controlling for the FFE, and vice-versa. Here, we present data simultaneously examining the FBOE and FFE for male androphilia in a large dataset collected in Samoa across 10 y of fieldwork, which only shows evidence of the FBOE.

Inter-sexual Mate Competition in Humans: A Historical Example from Seventeenth Century Portugal.

Inter-sexual mate competition occurs any time opposite-sex individuals simultaneously seek to acquire or maintain exclusive access to the same sexual partner. This underappreciated form of mate competition has been anecdotally documented in several avian and mammalian species, and systematically described among Japanese macaques and humans. Here, we extend the concept of inter-sexual mate competition by reassessing a remarkable series of Portuguese letters, penned in 1664 and later discovered and translated by Mott and Assunção (J Homosex 16:91-104, 1989). The letters comprise one side of a correspondence between two males, former lovers who were scrutinized by the Portuguese Inquisition. After ending the relationship, the recipient of the letters was betrothed to a woman, which provoked a jealous response from his jilted male lover and pleas to reunite. We argue that the letters portray a prolonged sequence of inter-sexual mate competition in which a male and female competitor vied for the same man. An established taxonomy of mate competition tactics was applied to the behavior of both competitors illustrating many parallels with contemporary examples of inter-sexual mate competition. Through this comparison, we show that modern mate competition taxonomies can be fruitfully applied to historical texts and that inter-sexual mate competition occurred hundreds of years before the present. Other examples of inter-sexual mate competition are likely to exist in the historical record, providing a rich source of scientific information if appropriate theoretical frameworks are employed. Indeed, any time individuals are attracted to sexual partners who behave in a bisexual manner, then inter-sexual mate competition can ensue with members of the other sex.

Sex and Sexual Orientation Differences in Dark Triad Traits, Sexual Excitation/Inhibition, and Sociosexuality.

The present study sought to investigate sex and sexual orientation differences in several traits related to sexuality and sexual behavior. Examining sexual orientation differences alongside basic sex differences to help identify correlates of sexual orientation diversity, and whether individuals with varying degrees of same-sex attraction show concurrent sex-atypical shifts in other domains. Males tend to score higher than females in the Dark Triad (DT) traits of sub-clinical narcissism, psychopathy, and Machiavellianism. Similarly, females tend to be more cautious than males in their attitudes and desires toward casual sex activity (i.e., sociosexuality). These sex differences may be related to the propensity for individuals to become easily sexually excited, which is higher in males, or to instead inhibit sexual arousal, which is higher in females. In a large undergraduate sample (N = 2047), we replicated expected sex differences in DT traits, sociosexuality, and sexual excitation/inhibition. We found that non-heterosexual females were "male-shifted" in some of these traits, but these shifts tended to be strongest among mostly heterosexual and bisexual individuals. Furthermore, we found that within-sex variation in sociosexuality, sexual excitation, and sexual inhibition was not related to sexual orientation in a linear fashion. Instead, sociosexuality and sexual excitation were related to sexual orientation in a curvilinear (inverted-U) fashion, especially among females. The fact that traits correlated with bisexuality and homosexuality were somewhat distinct is consistent with the idea that different developmental pathways may lead to these discrete sexual attraction patterns.

Occupational Preferences, Childhood Behavior, and Openness: The Role of Sex, Sexual Orientation, and Gender Identity in Iran.

Previous research suggests that both same-sex attraction and the personality trait "openness" are associated with sex-atypical preferences and behaviors. Here, we examined the links between adulthood occupational preferences, childhood play behavior, and openness among Iranian cisgender gynephilic males (n = 228), cisgender ambiphilic males (n = 48), cisgender androphilic males (n = 178), transgender androphilic males (n = 58), cisgender androphilic females (n = 226), cisgender ambiphilic females (n = 94), cisgender gynephilic females (n = 31), and transgender gynephilic females (n = 121) from Iran. Cisgender and transgender same-sex attracted males and females exhibited sex-atypical occupational preferences with the latter group showing even more sex-atypicality than the former. The personality trait openness did not differ between cisgender groups. Transgender androphilic males had a significantly higher mean score for openness compared to cisgender androphilic females and transgender gynephilic females, whereas transgender gynephilic females had a significantly lower mean score compared to cisgender androphilic males. In both males and females, childhood sex-atypicality, same-sex attraction, and openness were associated with sex-atypical occupational preferences. Our findings from Iran provides cross-cultural support for interconnectedness of childhood and adulthood sex-atypicality, openness, and same-sex attraction in males and females who are cisgender and transgender.

Heterosexual Men's Visual Attention to Nude Images Depicting Cisgender Males, Cisgender Females, and Gynandromorphs.

Gynandromorphophilia refers to sexual attraction and arousal to feminine males, who may or may not have breasts, and who retain their penises. Previous research has suggested that some capacity for gynandromorphophilia may characterize males who are gynephilic (i.e., sexually attracted and aroused to adult females). This study examined Canadian cisgender gynephilic men's (n = 65) visual attention and subjective ratings of sexual arousal when presented with nude images of feminine males with, and without breasts, masculine males, and feminine females. Visual attention was assessed using an infrared eye-tracker. Subjective arousal to feminine females was highest, followed by subjective arousal to feminine males with breasts, feminine males without breasts, and masculine males. However, subjective arousal to feminine males without breasts and to masculine males did not differ significantly. The patterning of visual attention to images of females was unique, in that participants were equally likely to attend first to the face, chest or genitals. These areas also elicited relatively greater fixation durations and counts. Although participants fixated onto the chests of feminine males with breasts for longer durations than those of masculine males, most of the differences between feminine males, with and without breasts, were non-significant. These results suggest that female sex-based traits play a more primary role in gynephilic men's sexual arousal than feminine gender-based traits.

Fertility Status Does Not Facilitate Women's Judgment of Male Sexual Orientation.

Previous research has demonstrated that women can correctly distinguish between gay and heterosexual men's faces significantly better than chance. This ability appears to be heightened during the most fertile portion of their ovulatory cycle. Here, we sought to replicate and extend these findings in a large sample of undergraduate women (N = 1960). Although women correctly identified men's sexual orientation significantly better than chance (62% average accuracy), a subsample of naturally cycling women (n = 426) did not judge men's sexual orientation from faces more accurately when in the fertile phase of their ovulatory cycle. These results further replicate the visibility of male sexual orientation, but do not show that this ability has strong links to estimated fertility.

When males have females on their backs: Male's tolerance, solicitation, and use of female-male mounting in Japanese macaques.

Previous research on Japanese macaques has shown that female-to-male mounting (FMM) is performed by some females as an exaggerated form of sexual solicitation that may occur in the context of high female competition for male mates. This supernormal courtship behavior functions to prompt subsequent male-to-female mounting. In this report, we focused on the male consort partners' responses to FMM. We studied a free-ranging population of Japanese macaques at Arashiyama, Japan, in which FMM is frequent and prevalent. We analyzed 240 consortships involving 31 females and 19 males. We tested three hypotheses regarding male's tolerance, solicitation, and use of FMM. First, we found that FMM was tolerated by male mountees who were no more likely to aggress their female partners during a short time window around a FMM than they were during the rest of the consortship period. Second, we showed that FMM could be triggered by male recipients, via explicit male-to-female sexual solicitations. Third, we found that some males may utilize FMM in a quest for their own sexual stimulation, which sometimes culminated in masturbation by the male during FMM. Our findings indicate that male partners facilitate the expression of FMM both passively (via their tolerance) and actively (via their solicitation). In addition, FMM appears to enhance the sexual arousal of male partners during consortships. We argued that, for females to have expanded their repertoire of sexual solicitations by adopting FMM, male mates must have played a role in the evolutionary origins and maintenance of this nonconceptive but intense and powerful female mating tactic.

Samoan Men's Sexual Attraction and Viewing Time Response to Male-to-Feminine Transgender and Cisgender Adults.

In many different cultures, some men express sexual interest in male-to-feminine (MtF) transgender individuals, but others do not. We examined whether, in Samoa, men who are sexually interested in fa'afafine (Samoan MtF transgender individuals) (MSF; N = 40) differed from men who were exclusively sexually interested in women (MSW; N = 41) in terms of their self-reported sexual attraction and viewing times responses to images of MtF transgender individuals who were feminine (e.g., had feminine hairstyles, makeup) but had not undergone gender-affirming surgeries (e.g., breast augmentation), cisgender women, and cisgender men. MSF reported that images of MtF transgender individuals were sexually attractive, although somewhat less attractive than images of cisgender women. In contrast, MSW reported that images of cisgender women were sexually attractive, but images of MtF transgender individuals were not. The groups did not differ in their sexual attraction ratings of men, which were uniformly low. MSF viewed MtF transgender individuals and cisgender women for a similar length of time and viewed both longer than cisgender men. In contrast, MSW viewed cisgender women longer than MtF transgender individuals and they viewed MtF transgender individuals longer than cisgender men. The present study indicates that responses to MtF transgender individuals vary among Samoan men who share a sexual preference for women.

Testing Women's Trust in Other Women and Same-Sex Attracted Males in Three Cultures.

Heterosexual women trust mating-relevant advice received from gay men more than that received from heterosexual women. This trust is predicated on women's perception that gay men lack ulterior sexual motives and romantically pursue other gay men. However, this trust may not hold in all cultures. For example, in both Samoa and the Istmo Zapotec of Southern Mexico, women take part in mate competition against feminine same-sex attracted males-referred to as fa'afafine and muxe, respectively-who regularly engage in sexual activity with masculine men. The present studies sought to replicate and extend research on women's trust in males who are same-sex attracted. Experiments were conducted in Canada, Samoa, and the Istmo Zapotec, with women randomly assigned to consider the likelihood of various mate-poaching behaviors performed by either a rival woman or a same-sex attracted male. In Canada, women were more trusting of cisgender gay men than other women. Similarly, Samoan women were more trusting of fa'afafine than other women. In the Istmo Zapotec, women were equally distrustful of women and feminine muxe gunaa, whereas more masculine muxe nguiiu were rated as more trustworthy than women and muxe gunaa. These results illustrate that women's trust in same-sex attracted males varies both between and within cultural contexts, perhaps impacted by the relative femininity of the male in question.

Meta-Analyses of Fraternal and Sororal Birth Order Effects in Homosexual Pedophiles, Hebephiles, and Teleiophiles.

This study investigated the relations between numbers of older brothers, numbers of older sisters, and the odds of homosexuality in later-born males, including males who are most attracted sexually to prepubescent or early pubescent children (pedohebephiles) and males who are most attracted sexually to adults (teleiophiles). The authors meta-analyzed data from 24 samples of homosexual and heterosexual men, originally reported in 18 studies, and totaling 18,213 subjects. The results confirmed that older brothers increase the odds of same-sex preference in pedohebephiles as they do in teleiophiles. They also replicated the recent finding that older sisters have a similar but weaker statistical association with the odds of homosexuality. These findings have two theoretical implications. First, the findings for older brothers and older sisters indicate some commonality in the factors that influence sexual preference in teleiophiles and those that influence sexual preference in pedohebephiles. Second, the finding for older sisters confirms a prediction stemming from the hypothesis that male fetuses stimulate maternal antibodies that increase the odds of homosexuality in later-born males. Such immunization could result from miscarried as well as full-term fetuses, and number of older sisters should correlate with number of male fetuses miscarried before gestation of the subject.

A method yielding comparable estimates of the fraternal birth order and female fecundity effects in male homosexuality.

The fraternal birth order effect (FBOE) is the finding that older brothers increase the probability of homosexuality in later-born males, and the female fecundity effect (FFE) is the finding that the mothers of homosexual males produce more offspring than the mothers of heterosexual males. In a recent paper, Khovanova proposed a novel method for computing independent estimates of these effects on the same samples and expressing the magnitude and direction of the effects in the same metric. In her procedure, only families with one or two sons are examined, and daughters are ignored. The present study investigated the performance of Khovanova's method using archived data from 10 studies, comprising 14 samples totalling 5390 homosexual and heterosexual subjects. The effect estimate for the FBOE showed that an increase from zero older brothers to one older brother is associated with a 38% increase in the odds of homosexuality. By contrast, the effect estimate for the FFE showed that the increase from zero younger brothers to one younger brother is not associated with any increase in the odds of homosexuality. The former result supports the maternal immune hypothesis of male homosexuality; the latter result does not support the balancing selection hypothesis.

A Retrospective Study of Childhood Sex-Typed Behavior in Istmo Zapotec Men, Women, and Muxes.

Previous research has consistently demonstrated that both transgender and cisgender androphilic males (i.e., males attracted to adult males) display and recall higher levels of childhood female-typical behavior (CFTB) and lower levels of childhood male-typical behavior (CMTB) compared to gynephilic males (i.e., males attracted to adult females). In adulthood, the recalled CFTB and CMTB scores of cisgender androphilic males tend to be intermediate to those of opposite-sex-attracted men and women, whereas transgender androphilic males tend to score similar to women. These studies have been mostly conducted in Euro-American cultures. We examined recalled childhood sex-typed behavior (CSTB) among the Istmo Zapotec-a pre-Colombian culture in the Istmo region of Oaxaca, Mexico, where cisgender and transgender androphilic males are recognized as a third gender, known locally as muxes. The present study sought to determine whether Istmo Zapotec men (n = 180), cisgender muxe nguiiu (n = 63), transgender muxe gunaa (n = 120), and women (n = 138) differ with respect to recalled CFTB and CMTB. Our results indicate that men recalled significantly less CFTB and more CMTB than women. Cisgender muxes scored in between men and women. Transgender muxes scored similar to women. These findings provide further evidence that childhood sex-atypical behavior is a cross-culturally universal and normative developmental aspect of male androphilia, regardless of whether it manifests in the cisgender or transgender form. This is the first study to present quantitative data comparing the recalled CSTB of cisgender and transgender androphilic males from within the same non-Euro-American culture.

Offspring Production Among the Relatives of Istmo Zapotec Men and Muxes.

Male androphilia (i.e., sexual attraction toward adult males) is influenced by biological factors, reliably occurs across diverse cultures, and has persisted over evolutionary time despite the fact that it reduces reproduction. One possible solution to this evolutionary paradox is the sexually antagonistic gene hypothesis (SAGH), which states that genes associated with male androphilia reduce reproduction when present in males but increase reproduction when present in their female relatives. The present study tested the SAGH among the Istmo Zapotec-a non-Euro-American culture in Oaxaca, Mexico, where transgender and cisgender androphilic males are known as muxe gunaa and muxe nguiiu, respectively. To test the SAGH, we compared offspring production by the biological relatives of muxe gunaa (n = 115), muxe nguiiu (n = 112), and gynephilic men (i.e., cisgender males who are sexually attracted to adult females; n = 171). The mothers and paternal aunts of muxe gunaa had higher offspring production than those of muxe nguiiu. Additionally, the relatives of muxe gunaa had more offspring than those of gynephilic men, whereas no such differences were found between the families of gynephilic men and muxe nguiiu. Elevated reproduction by the mothers and, particularly the aunts, of muxe gunaa is consistent with the SAGH. However, the absence of group differences between gynephilic men and muxe nguiiu, and the group differences between the two types of muxes are not predicted by the SAGH. This is the first study to demonstrate reproductive differences between kin of transgender and cisgender androphilic males within the same non-Euro-American culture.

Prevalence of Sexual Orientation Across 28 Nations and Its Association with Gender Equality, Economic Development, and Individualism.

The prevalence of women's and men's heterosexuality, bisexuality, and homosexuality was assessed in 28 nations using data from 191,088 participants from a 2005 BBC Internet survey. Sexual orientation was measured in terms of both self-reported sexual identity and self-reported degree of same-sex attraction. Multilevel modeling analyses revealed that nations' degrees of gender equality, economic development, and individualism were not significantly associated with men's or women's sexual orientation rates across nations. These models controlled for individual-level covariates including age and education level, and nation-level covariates including religion and national sex ratios. Robustness checks included inspecting the confidence intervals for meaningful associations, and further analyses using complete-cases and summary scores of the national indices. These analyses produced the same non-significant results. The relatively stable rates of heterosexuality, bisexuality, and homosexuality observed across nations for both women and men suggest that non-social factors likely may underlie much variation in human sexual orientation. These results do not support frequently offered hypotheses that sexual orientation differences are related to gendered social norms across societies.

Heterogeneity in the Sexual Orientations of Men Who Have Sex with Fa'afafine in Samoa.

In Samoa, feminine natal males who possess male-typical genitalia are known locally as fa'afafine. Some Samoan men express sexual interest in fa'afafine, whereas others do not. To assess the sexual orientation of men who are sexually interested in fa'afafine, we collected sexual attraction ratings and viewing times of Samoan men's and women's faces. Study 1 (N = 130) focused on men who were insertive or versatile during anal sex with fa'afafine partners. These men were compared to each other, as well as to males (i.e., men and fa'afafine) who were exclusively sexually interested in either women or men. Study 2 (N = 180) compared men who had sex with fa'afafine and women; men who had sex with fa'afafine, women, and men; and men who had sex with fa'afafine and men. These men were compared to each other, as well as to males who were exclusively sexually interested in either women or men. These studies suggest that men who have sex with fa'afafine are a heterogeneous group. A small portion of the men who are sexually interested in fa'afafine shows a relatively bisexual pattern of sexual attraction ratings and viewing times, namely men who have sex with fa'afafine, men, and women. In contrast, a larger number of men who were sexually interested in fa'afafine responded in a manner similar to men who were exclusively sexually interested in either women or men. The present research suggests that additional insights into male sexual orientation can be garnered by focusing on how sexuality is expressed in non-Western cultural contexts.

The relationship between fraternal birth order and childhood sex-atypical behavior among the Istmo Zapotec muxes.

Research on male androphilia (i.e., sexual attraction towards adult males) consistently finds that androphilic males tend to have more older biological brothers than males who are gynephilic (i.e., sexually attracted to adult females). This fraternal birth order effect (FBOE) has been well replicated among androphilic males who present publically in a male-typical (cisgender) and a female-typical (transgender) manner. There is some evidence that the FBOE is more pronounced among transgender androphilic males. However, no studies have directly compared both forms of male androphilia within the same culture. This study tested the FBOE, and its association with childhood sex-atypical behavior (CSAB), among the Istmo Zapotec of Oaxaca, Mexico, where both forms of male androphilia are referred to as a third gender, muxes. Our results indicated that both cisgender muxe nguiiu (n = 124) and transgender muxe gunaa (n = 120) were more likely to be later born among brothers than gynephilic men (n = 194). However, the number of older brothers did not differentiate between transgender and cisgender muxes, nor did it predict CSAB among muxes. These findings replicate the FBOE among both cisgender and transgender muxes but show no evidence that it is more pronounced among transgender androphilic males.

Hormonal contraceptive affects heterosexual but not homosexual behavior in free-ranging female Japanese macaques over 17 mating seasons.

We assessed the effect of a progestin-based contraceptive treatment (chlormadinone acetate) on female heterosexual and homosexual behaviors in a free-ranging group of Japanese macaques (Macaca fuscata) living at Arashiyama-Kyoto, Central Japan. The data included estimated intensity of fertility cues, sexual solicitations and mounting behaviors collected daily during 17 consecutive mating seasons (1995-2012) from 159 females. Females that were on contraception: (1) exhibited less intense cues of putative fertility and for shorter periods; (2) were solicited by fewer males, and those males that did solicit them did so less often (i.e., lower heterosexual attractivity); (3) solicited fewer males and when they did perform sexual solicitations they did so less often (i.e., lower heterosexual proceptivity); (4) engaged in shorter heterosexual consortships with fewer male partners (i.e., lower heterosexual receptivity), compared with females that were not on contraception. In contrast, contraceptive treatment had no significant effect on the prevalence, occurrence, frequency, or duration of female homosexual behaviors. Even though heterosexual and homosexual behaviors can both be considered sexual in character and under hormonal control, our results suggested they are, to some extent, dissociable. Because females engaging in homosexual interactions showed less intense cues of putative fertility than those engaging in heterosexual interactions, regardless of contraceptive treatment, we argued that the hormonal threshold required for the expression of heterosexual behavior by females was associated with elevated sex hormones levels compared to homosexual behavior. We discussed the hormonal correlates of sexual behavior and partner preferences in Japanese macaques.

Deer Mates: A Quantitative Study of Heterospecific Sexual Behaviors Performed by Japanese Macaques Toward Sika Deer.

This is the first quantitative study of heterospecific sexual behavior between a non-human primate and a non-primate species. We observed multiple occurrences of free-ranging adolescent female Japanese macaques (Macaca fuscata) performing mounts and sexual solicitations toward sika deer (Cervus nippon) at Minoo, central Japan. Our comparative description of monkey-deer versus monkey-monkey interactions supported the "heterospecific sexual behavior" hypothesis: the mounts and demonstrative solicitations performed by adolescent female Japanese macaques toward sika deer were sexual in nature. In line with our previous research on the development of homospecific sexual behavior in immature female Japanese macaques, this study will allow us to test other hypotheses in the future, such as the "practice for homospecific sex," the "safe sex," the "homospecific sex deprivation," the "developmental by-product," and the "cultural heterospecific sex" hypotheses. Further research will be necessary to ascertain whether this group-specific sexual behavior was a short-lived fad or an incipient cultural phenomenon and may also contribute to better understanding the proximate and ultimate causes of reproductive interference.

The Relationship Between Indicators of Depression and Anxiety and Sexual Orientation in Canadian Women.

Previous studies examining the associations between women's sexual orientation and mental health have obtained inconsistent results. Whereas some studies have suggested that status as a lesbian or bisexual woman may be associated with greater mental health risk, others have suggested that bisexual women may be specifically vulnerable to mental health problems. The current study examined two competing models in a non-clinical sample of Canadian women (N = 278). The first model predicted that women who reported bisexual attraction would endorse more indicators of depression and anxiety compared to women who reported monosexuality (either same- or opposite-sex attraction). The second model predicted that women who reported relatively greater same-sex attraction would exhibit elevated indicators of depression and anxiety compared to women who reported opposite-sex attraction. Consistent with Model 1, greater bisexual attraction predicted greater endorsement of indicators of depression and anxiety compared to greater same-sex or opposite-sex attraction. These findings suggest that, in women, bisexuality may be associated with higher risk of depression and anxiety than monosexuality. Future research may benefit from exploring risk factors potentially unique to the mental health of bisexual women.