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.

A Test of the Kin Selection Hypothesis for Female Gynephilia in Thailand.

Female gynephilia (i.e., sexual attraction to adult females) is considered an evolutionary paradox because it reduces direct reproduction, yet it is influenced by genetic factors and has persisted over time and across different cultures. The Kin Selection Hypothesis proposes that same-sex attracted individuals offset their lowered direct reproduction by engaging in kin-directed altruism that increases the reproduction of close genetic relatives, thereby enhancing inclusive fitness. Previous research on male same-sex attraction found evidence to support this hypothesis in some cultures. The present study employed a Thai sample to compare altruistic tendencies towards kin and non-kin children in heterosexual women (n = 285), lesbian women (n = 59), toms (i.e., masculine gynephilic females who take on a nonbinary gender identity; n = 181), and dees (i.e., feminine gynephilic females who are attracted to toms; n = 154). The Kin Selection Hypothesis of same-sex attraction predicts that gynephilic groups would show increased kin-directed altruism compared with heterosexual women, but we did not find evidence supporting this prediction. Instead, the tendency to invest more towards kin than non-kin children was more exaggerated in heterosexual women than lesbian women. Also, heterosexual women showed greater dissociation between kin and non-kin altruistic tendencies compared with toms and dees, which may suggest the former's cognition is better attuned for kin-directed altruism. Thus, the present findings were contrary to the Kin Selection Hypothesis for female gynephilia. Alternative explanations regarding the maintenance of genetic factors predisposing individuals to female gynephilia are discussed and require further investigation.

Intra- and Intersexual Mate Competition in Two Cultures : A Comparison of Women's Response to Mate Competition with Women and Gender-Nonbinary Males in Samoa and among the Istmo Zapotec.

The present study examined women's mate competition tactics in response to female and feminine-male rivals in two cultures in which competition against both occurs. In Samoa and the Istmo Zapotec (Southern Mexico), women not only compete with other women (intrasexually) but also compete with rival feminine males (intersexually) in order to access/retain the same masculine men as sexual/romantic partners. Using a mixed-method paradigm, women were asked about their experiences of intra- and intersexual mate competition, and these narratives were recorded. The tactics reportedly employed by participants, and those attributed to mate competitors, were categorized according to established taxonomies of mate competition tactics, and their frequencies compared. Within-culture, the likelihood that participant women had ever experienced intra- and intersexual mate competition did not differ. Furthermore, participants reported a similar pattern of behavioral tactics whether their rival was another woman or a feminine male. These included benefit provisioning tactics during mate acquisition and cost-inflicting tactics during mate retention. Similarly, the mate competition tactics attributed to rival women and rival feminine males bore a striking resemblance, focused on enticing target men. Results highlight the mate competition tactics employed by women outside of a Euro-American context, and the way cultural factors impact mating landscapes presumed to be exclusively heterosexual. The presence of feminine males, alongside masculine men's willingness to engage in sexual activity with them, induces women in such cultures to compete intersexually in comparable ways to intrasexual competition with rival women.

Confounds, Causality, and Sexual Orientation: The Implications of a Population-Level Study of Sibling Characteristics and Same-Sex Attraction.

Representative samples, and especially population samples, are coveted sources of high-quality data in psychological science. In their recent article, Ablaza et al. (2021) used a population sample of marriages and registered partnerships in the Netherlands to examine the relationships between sibling characteristics and sexual orientation. We discuss the implications of this work for understanding the fraternal and sororal birth order effects on male and female same-sex attraction, and how both relate to maternal reproduction. The causal assumptions of these findings are explored, as well as the necessity of population-level data, and whether the data presented by Ablaza et al. are truly representative of the Dutch population.

Facial Attractiveness of the Sisters of Istmo Zapotec Men and Muxes: Implications for the Evolution of Male Androphilia.

Research shows that the female relatives of androphilic (i.e., sexually attracted to adult males) males have more children than the female relatives of gynephilic (i.e., sexually attracted to adult females) males. The mechanisms by which this occurs are unclear. The hypergyny hypothesis suggests that the female relatives of androphilic males have elevated attractiveness which allows them to obtain male partners with higher socioeconomic status, which in turn, provide them with more resources to produce and sustain multiple offspring. We tested whether the female kin of male androphiles are characterized by elevated attractiveness compared to the female kin of male gynephiles. The research was conducted among the Istmo Zapotec from Oaxaca, Mexico, where androphilic males are recognized as a third gender, muxes. We recruited 115 gynephilic men who rated the facial attractiveness of 27 women with at least one muxe sibling and 27 women with only gynephilic male siblings (i.e., control sisters). The results showed that gynephilic men found the faces of control sisters more attractive than the faces of muxe sisters. This finding is inconsistent with the hypergyny hypothesis and suggests that elevated facial attractiveness is not the mechanism by which the female relatives of androphilic males achieve elevated reproduction.

Occupational Preferences and Recalled Childhood Sex-Atypical Behavior among Istmo Zapotec Men, Women, and Muxes.

Research has found that both cisgender and transgender androphilic males (i.e., males sexually attracted to and aroused by other adult males) have female-typical occupational preferences when compared with gynephilic males (i.e., males sexually attracted to and aroused by adult females). Moreover, whereas cisgender androphilic males' occupational preferences tend to be intermediate between those of gynephilic men and androphilic women, transgender androphilic males tend to have occupational preferences that are more similar to androphilic women. No study has directly compared both types of androphilic males within the same culture. The present study investigated occupational preference and its relation to childhood sex-atypical behavior (CSAB), among gynephilic men (n = 208), androphilic women (n = 138), and cisgender (n = 132) and transgender (n = 129) androphilic males from the Istmo region of Oaxaca, Mexico, where androphilic males are recognized as third gender, muxes. The study found large sex differences in occupational preferences (d = 2.80). Furthermore, both cisgender muxe nguiiu (d = 2.36) and transgender muxe gunaa (d = 3.44) reported having more sex-atypical occupational preferences compared with men. However, muxe gunaa reported higher female-typical occupational preferences than women (d = 0.59) and muxe nguiiu (d = 0.57), whereas muxe nguiiu and women did not differ (d = 0.08). These findings are consistent with the conclusion that sex-atypical occupational preferences are a cross-culturally universal aspect of male androphilia. Finally, CSAB was associated with sex-atypical occupational preferences among all participants. These findings suggest that a developmental continuity exists between childhood and adulthood sex-atypicality.

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.

Women's Reaction to Opposite- and Same-Sex Infidelity in Three Cultures : Data from Canada, Samoa, and the Istmo Zapotec.

Previous research indicates that Euro-American women are more upset by imagining their male partners committing homosexual infidelities than heterosexual ones. The present studies sought to replicate these findings and extend them to two non-Western cultures wherein masculine men frequently engage in sexual interactions with feminine third-gender males. Across six studies in three cultural locales (Canada, Samoa, and the Istmo Zapotec), women were asked to rate their degree of upset when imagining that their partner committed infidelity that was heterosexual in nature, as well as infidelity that was homosexual. In two Canadian undergraduate samples, women reported greater upset at imagining partner infidelity with a female, whereas a community sample of middle-aged women reported equal upset across infidelity types. Samoan women reported substantially less upset at the thought of partner infidelity with a third-gender male (fa'afafine) than with a female. Istmo Zapotec women reported equal upset toward infidelity with a female or a third-gender male (muxe), whereas a second Zapotec sample reported slightly greater upset at the thought of infidelity with a muxe. Results illustrate how cultural contexts moderate the degree to which same-sex infidelity scenarios are upsetting to women.

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.

Inter-sexual mate competition in three cultures.

Darwinian sexual selection theory holds that mate selection occurs inter-sexually, and mate competition occurs intra-sexually for opposite-sex partners. We demonstrate that inter-sexual mate competition can also occur among humans at appreciable rates that vary by culture. In Canada, inter-sexual mate competition was both rare and inconsequential. However, data from two disparate non-Western cultures-Samoa and the Istmo Zapotec (Oaxaca, Mexico)-show that women frequently compete with feminine same-sex attracted males to acquire and maintain masculine male mates (i.e., men). Inter-sexual mate competition most commonly involved feminine males attempting to poach women's masculine male sexual partners. During these interactions, women and feminine males both attempted to manipulate the man who was the object of sexual competition; feminine males attempted to entice the target man, whereas women engaged in guarding and emotionally punitive behaviours. We do not anticipate that inter-sexual mate competition will be common in most species or across all cultures. However, when males and females prefer the same sexual partners, who themselves behave in a bisexual manner, then inter-sexual mate competition can ensue.

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.

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.

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.