Offspring production among the extended relatives of Samoan men and fa'afafine

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.

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.

Are Sibship Characteristics Predictive of Same Sex Marriage? An Examination of Fraternal Birth Order and Female Fecundity Effects in Population-level Administrative Data from the Netherlands

Despite historical increases in the number of individuals engaging in same-sex relations and entering same-sex unions, the causes of sexual orientation remain an open question. Two biological processes that have received some degree of empirical validation are the fraternal birth-order effect (FBOE) and the female-fecundity effect (FFE). Respectively, these processes posit that having a greater number of older brothers and being part of larger sibships independently increase the odds of male homosexuality. Nevertheless, previous studies have relied on suboptimal data and methods, including underpowered and selected samples, and models that fail to fully disentangle the two processes. In addition, they have rarely analyzed samples of women. We address these limitations using high-quality, population-level linked register data from the Netherlands (n = 9,073,496). Applying a novel multivariable approach, we jointly examine the FBOE and FFE by comparing the sibship characteristics of men (n = 26,542) and women (n = 33,534) who entered a same-sex union against those who did not (n = 4,607,785 men and 4,405,635 women). Our analyses yield robust evidence of an FBOE on both male and female homosexuality, but no support for the FFE. Additionally, we find that individuals' birth order affects the probability of entering a same-sex union, regardless of the sex of older siblings.

Facial Attractiveness of Sisters of Thai Gay Men and Sao Praphet Song

Androphilia refers to sexual attraction toward adult males. Androphilic males' female genetic relatives might offset the fitness cost of androphilia by having elevated numbers of offspring. Increased attractiveness relative to other women may enable these females to marry up the social hierarchy, providing greater access to resources to support more offspring. In Thailand, there is a marked status hierarchy and male androphiles are highly visible - identifying as gay men or as a third gender known as sao praphet song. Thus, a field experiment was conducted in which 208 heterosexual men rated the facial attractiveness of 25 sisters of Thai gay men or sao praphet song and 25 comparison women with no known same-sex attracted relatives. Contrary to the prediction, the comparison group was rated as more attractive than the sisters, casting doubt on hypotheses that posit greater attractiveness of female relatives of male androphiles as a proximate mechanism facilitating the evolutionary maintenance of genes influencing male androphilia. Also, men from rural areas rated the women, regardless of group, as more attractive than men from urban areas, consistent with some prior studies showing rural-urban differences in perceptions of attractiveness.

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.

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 Comparison of the Reproductive Output Among the Relatives of Samoan Androphilic Fa'afafine and Gynephilic Men

The sexually antagonistic gene hypothesis (SAGH) for male androphilia posits that genes associated with androphilia (i.e., sexual attraction to adult males) will result in lowered reproduction when present in males, but increased reproduction when present in females. Findings derived from some Western European samples furnish support for the SAGH; however, results from studies conducted in other regions of the world have been more equivocal. Our previous research in Samoa indicated that the mothers as well as the maternal and paternal grandmothers of androphilic males (known locally as fa'afafine) exhibit elevated reproductive output when compared to the relatives of gynephilic men (i.e., males that are sexually attracted to adult females). The present replication study tested the SAGH in Samoa using a sample that was 122 % larger than the one previously studied by our group (VanderLaan, Forrester, Petterson, & Vasey, 2012). In line with the predictions of the SAGH, we hypothesized that the grandmothers, aunts, and mothers of fa'afafine would show elevated reproductive output compared to those of Samoan gynephilic men. Data were collected from 191 fa'afafine and 191 gynephilic men on the reproductive output of their paternal and maternal biological relatives (i.e., mothers, grandmothers, aunts, uncles). The mothers and maternal grandmothers of fa'afafine showed elevated reproductive output compared to those of gynephilic men. The paternal grandmother effect was not replicated. Although these results are consistent with the SAGH, a lack of difference in the reproductive output of aunts renders support for the SAGH in Samoa equivocal.

Recalled Separation Anxiety in Childhood in Istmo Zapotec Men, Women, and Muxes

The Istmo Zapotec are a pre-Columbian cultural group indigenous to the Istmo region of Oaxaca, Mexico. Istmo Zapotec recognize three genders: men, women, and muxes. Like Istmo Zapotec men, muxes are biological males. However, unlike Istmo Zapotec men, most muxes are exclusively androphilic (i.e., sexually attracted to adult males), relatively feminine, and routinely adopt the receptive role during anal intercourse. Furthermore, the Istmo Zapotec recognize two types of muxes: muxe gunaa, who resemble the transgender androphilic males that are common in many non-Western cultures, and muxe nguiiu, who resemble the cisgender androphilic males ("gay" men) common in Western cultures. Retrospective research conducted in Canada and Samoa demonstrates that cisgender and transgender androphilic males recall elevated indicators of childhood separation anxiety (i.e., feelings of distress related to separation from major attachment figures) when compared to males who are gynephilic (i.e., sexually attracted to adult females). The present study compared recalled indicators of childhood separation anxiety among Istmo Zapotec men, women, muxe gunaa, and muxe nguiiu (N = 454). Men recalled significantly lower levels of childhood separation anxiety compared to all other groups (all p < .042). No additional group differences were found. Our results are consistent with previous research conducted in Canada and Samoa, suggesting that elevated childhood separation anxiety is a developmental correlate of male androphilia that is cross-culturally universal. This research is also consistent with the conclusion that cisgender and transgender male androphiles share a common biological and developmental foundation despite being different in appearance.

Sexual Orientation, Controversy, and Science

Summary

Ongoing political controversies around the world exemplify a long-standing and widespread preoccupation with the acceptability of homosexuality. Nonheterosexual people have seen dramatic surges both in their rights and in positive public opinion in many Western countries. In contrast, in much of Africa, the Middle East, the Caribbean, Oceania, and parts of Asia, homosexual behavior remains illegal and severely punishable, with some countries retaining the death penalty for it. Political controversies about sexual orientation have often overlapped with scientific controversies. That is, participants on both sides of the sociopolitical debates have tended to believe that scientific findings—and scientific truths—about sexual orientation matter a great deal in making political decisions. The most contentious scientific issues have concerned the causes of sexual orientation—that is, why are some people heterosexual, others bisexual, and others homosexual? The actual relevance of these issues to social, political, and ethical decisions is often poorly justified, however.

A test of genetic models for the evolutionary maintenance of same-sex sexual behaviour

The evolutionary maintenance of same-sex sexual behaviour (SSB) has received increasing attention because it is perceived to be an evolutionary paradox. The genetic basis of SSB is almost wholly unknown in non-human animals, though this is key to understanding its persistence. Recent theoretical work has yielded broadly applicable predictions centred on two genetic models for SSB: overdominance and sexual antagonism. Using Drosophila melanogaster, we assayed natural genetic variation for male SSB and empirically tested predictions about the mode of inheritance and fitness consequences of alleles influencing its expression. We screened 50 inbred lines derived from a wild population for male-male courtship and copulation behaviour, and examined crosses between the lines for evidence of overdominance and antagonistic fecundity selection. Consistent variation among lines revealed heritable genetic variation for SSB, but the nature of the genetic variation was complex. Phenotypic and fitness variation was consistent with expectations under overdominance, although predictions of the sexual antagonism model were also supported. We found an unexpected and strong paternal effect on the expression of SSB, suggesting possible Y-linkage of the trait. Our results inform evolutionary genetic mechanisms that might maintain low but persistently observed levels of male SSB in D. melanogaster, but highlight a need for broader taxonomic representation in studies of its evolutionary causes.

Male Homosexual Preference: Where, When, Why?

Male homosexual preference (MHP) has long been of interest to scholars studying the evolution of human sexuality. Indeed, MHP is partially heritable, induces a reproductive cost and is common. MHP has thus been considered a Darwinian paradox. Several questions arise when MHP is considered in an evolutionary context. At what point did MHP appear in the human evolutionary history? Is MHP present in all human groups? How has MHP evolved, given that MHP is a reproductively costly trait? These questions were addressed here, using data from the anthropological and archaeological literature. Our detailed analysis of the available data challenges the common view of MHP being a "virtually universal" trait present in humans since prehistory. The conditions under which it is possible to affirm that MHP was present in past societies are discussed. Furthermore, using anthropological reports, the presence or absence of MHP was documented for 107 societies, allowing us to conclude that evidence of the absence of MHP is available for some societies. A recent evolutionary hypothesis has argued that social stratification together with hypergyny (the hypergyny hypothesis) are necessary conditions for the evolution of MHP. Here, the link between the level of stratification and the probability of observing MHP was tested using an unprecedented large dataset. Furthermore, the test was performed for the first time by controlling for the phylogenetic non-independence between societies. A positive relationship was observed between the level of social stratification and the probability of observing MHP, supporting the hypergyny hypothesis.

Testing the Affiliation Hypothesis of Homoerotic Motivation in Humans: The Effects of Progesterone and Priming

The frequency of homoerotic behavior among individuals who do not identify as having an exclusively homosexual sexual orientation suggests that such behavior potentially has adaptive value. Here, we define homoerotic behavior as intimate erotic contact between members of the same sex and affiliation as the motivation to make and maintain social bonds. Among both male and female nonhuman primates, affiliation is one of the main drivers of homoerotic behavior. Correspondingly, in humans, both across cultures and across historical periods, homoerotic behavior appears to play a role in promoting social bonds. However, to date, the affiliation explanation of human homoerotic behavior has not been adequately tested experimentally. We developed a measure of homoerotic motivation with a sample of 244 men and women. Next, we found that, in women (n = 92), homoerotic motivation was positively associated with progesterone, a hormone that has been shown to promote affiliative bonding. Lastly, we explored the effects of affiliative contexts on homoerotic motivation in men (n = 59), finding that men in an affiliative priming condition were more likely to endorse engaging in homoerotic behavior compared to those primed with neutral or sexual concepts, and this effect was more pronounced in men with high progesterone. These findings constitute the first experimental support for the affiliation account of the evolution of homoerotic motivation in humans.

Societal Norms Rather Than Sexual Orientation Influence Kin Altruism and Avuncularity in Tribal Urak-Lawoi, Italian, and Spanish Adult Males

Homosexual males could balance their low fitness by increasing benefits to relatives either through kin-directed altruism or by avuncularity (altruistic behavior toward the children of siblings). Evidence in support of kin selection and avuncularity includes the fact that homosexuals seem to be more empathic and altruistic than heterosexuals. Other studies have not confirmed behaviors that increase kin altruism in homosexuals. We explored altruistic behavior and avuncularity in a sample of 278 subjects, either homosexual or heterosexual, from three populations: Italian, Spanish, and Urak-Lawoi, a Southeast Asian tribal population. Among the Urak-Lawoi, the kathoeys, androphilic men who dress and behave as women, were compared with heterosexuals. All populations were rated for societal norms on the expression of affiliative behavior. No greater kin altruism or avuncularity among the kathoeys or in homosexuals in either Mediterranean population was found. Greater avuncularity and kin-directed altruism, independent of sexual orientation, were found among the Urak-Lawoi, and these traits were the least prevalent among the Italians, corresponding to different societal norms. The increase in kin altruism and avuncularity was associated in all males with societal differences and norms on general altruism toward nonkin children, suggesting it is not an adaptive design to maintain homosexuality in humans.

On the evolutionary origins of differences in sexual preferences

A novel explanation of the evolutionary process leading to the appearance of differences in sexual preferences is proposed. The explanation is fully general: it is not specific to any particular type of sexual preferences, nor to any species or population. It shows how different sexual preferences can appear in any large group-living population in which sexual selection is sufficiently strong in each sex. The main idea is that the lack of interest toward a member of the opposite sex may be interpreted as a signal of popularity, and thus of reproductive success. It is then boosted by the Fisher runaway process far beyond the point where it becomes costly, resulting in a generalized trait-lack of interest toward the opposite sex. If the interest diverts toward other targets then different sexual preferences emerge. This hypothesis is placed into the context of other works on different sexual preferences in animals; supporting evidence from the literature is reviewed and additional research needed to confirm or refute the hypothesis in any given species is outlined.

Evolving research on the evolution of male androphilia

Androphilia refers to sexual attraction and arousal to adult males, whereas gynephilia refers to sexual attraction and arousal to adult females. The manner in which male androphilia is expressed varies cross-culturally. Sex-gender congruent male androphiles occupy the gender role typical of their sex, behave in a relatively masculine manner, and identify as “men.” In contrast, transgendered male androphiles often behave in a highly effeminate manner and identify as neither “men,” nor “women.” Instead, they typically identify as members of a third gender. Despite exhibiting different gender role presentations and gender identities, both forms of male androphilia share numerous biodemographic and developmental correlates, indicating that they have a common etiological basis. Male androphilia represents an evolutionary paradox because it appears to have a genetic component, yet it compromises reproduction. At the same time archaeological and cross-cultural evidence suggest that it has persisted for millennia. The ancestral form of male androphilia was likely the transgendered form. To date, only one population of transgendered male androphiles has been considered when testing hypotheses pertaining to the evolution of male androphilia: the fa'afafine of Samoa. Research indicates that the mothers, paternal grandmothers and maternal grandmothers of fa'afafine produce more offspring than those of male gynephiles, which is consistent with the Sexually Antagonistic Gene Hypothesis. However, definitive support for this hypothesis, in the form of elevated offspring production by the aunts of fa'afafine is lacking at present. Research also indicates that fa'afafine exhibit elevated avuncular tendencies and behaviour compared to women and gynephilic men, which is consistent with the Kin Selection Hypothesis. Also consistent with the Kin Selection Hypothesis is research indicating that the fa'afafine's avuncular cognition exhibits elements of adaptive design.

Evidence of cognitive biases for maximizing indirect fitness in Samoan fa'afafine

The kin selection hypothesis posits that male androphilia (i.e., sexual attraction to males), although detrimental to reproduction (i.e., direct fitness), has persisted and evolved because androphilic males compensate by increasing their indirect fitness via increased investment in kin. In previous studies, Samoan androphilic males (known locally as fa'afafine) reported elevated avuncular (i.e., uncle-like) tendencies compared to Samoan gynephilic (i.e., sexually attracted to females) men. Their avuncular tendencies were also greater than the materteral (i.e., aunt-like) tendencies of androphilic women. The present study examined whether the avuncular cognition of fa'afafine was enhanced for maximizing indirect fitness. To do so, it examined whether fa'afafine had a stronger propensity than Samoan gynephilic men and androphilic women to invest in kin categories that would result in more reliable and substantive increases in indirect fitness (i.e., young, female kin) in hypothetical investment scenarios. In a forced-choice paradigm, although all individuals showed some degree of bias to invest in adaptive kin categories during non-frivolous investment contexts in which the consequences of investment were relatively non-trivial, fa'afafine showed greater adherence to the predicted pattern. In addition, shifting the context from frivolous investments, in which the consequences of investment were relatively trivial, to non-frivolous investments prompted fa'afafine to exhibit an enhanced preference, relative to Samoan gynephilic men and androphilic women, to invest in adaptive kin categories. These findings were consistent with the kin selection hypothesis and suggest that, although all individuals exhibit cognitive biases for increasing indirect fitness, the avuncular cognition of androphilic males has undergone selective enhancement to maximize the accrual of indirect fitness via kin-directed altruism.

Male androphilia in the ancestral environment. An ethnological analysis

The kin selection hypothesis posits that male androphilia (male sexual attraction to adult males) evolved because androphilic males invest more in kin, thereby enhancing inclusive fitness. Increased kin-directed altruism has been repeatedly documented among a population of transgendered androphilic males, but never among androphilic males in other cultures who adopt gender identities as men. Thus, the kin selection hypothesis may be viable if male androphilia was expressed in the transgendered form in the ancestral past. Using the Standard Cross-Cultural Sample (SCCS), we examined 46 societies in which male androphilia was expressed in the transgendered form (transgendered societies) and 146 comparison societies (non-transgendered societies). We analyzed SCCS variables pertaining to ancestral sociocultural conditions, access to kin, and societal reactions to homosexuality. Our results show that ancestral sociocultural conditions and bilateral and double descent systems were more common in transgendered than in non-transgendered societies. Across the entire sample, descent systems and residence patterns that would presumably facilitate increased access to kin were associated with the presence of ancestral sociocultural conditions. Among transgendered societies, negative societal attitudes toward homosexuality were unlikely. We conclude that the ancestral human sociocultural environment was likely conducive to the expression of the transgendered form of male androphilia. Descent systems, residence patterns, and societal reactions to homosexuality likely facilitated investments in kin by transgendered males. Given that contemporary transgendered male androphiles appear to exhibit elevated kin-directed altruism, these findings further indicate the viability of the kin selection hypothesis.

Comparative reproductive output of androphilic and gynephilic males in samoa

Debate exists in the behavioral sciences regarding the extent to which androphilic males reproduce compared to their gynephilic counterparts. Quantitative data that might speak to this debate are surprisingly rare. Here, we compared the reproductive output of 235 transgendered, exclusively androphilic Samoan males (known locally as fa'afafine) to that of 447 exclusively gynephilic Samoan males. Samoan gynephilic male participants fathered significantly more children than fa'afafine participants. In fact, none of the fa'afafine in our sample produced offspring. On the basis of this evidence and anecdotal accounts in the anthropological literature, we contend that absence of reproductive output is a near absolute cross-cultural universal characterizing non-Western, transgendered androphilic ("third-gender") males. Models for the evolution of male androphilia must account for how genes associated with this sexual orientation originated in the past and persisted in populations over time despite the fact that the vast majority of androphilic males have no direct reproductive success.

The prevalence of fa'afafine relatives among Samoan gynephilic men and fa'afafine

Androphilia refers to sexual attraction to adult males whereas gynephilia refers to sexual attraction to adult females. In Western populations, androphilia in males is familial, but the precise nature of this phenomenon is unclear. Some studies show that androphilic males have preponderances of androphilic male relatives in the maternal, but not paternal, line. In contrast, other studies show that male androphilia clusters in both the maternal and paternal lines. Low fertility populations are susceptible to producing anomalous patterns with respect to biodemographic correlates of male sexual orientation, which may account for discrepancies in the familial patterning of male androphilia across Western studies. We focused on a high fertility population to determine which pattern, if any, prevailed. The prevalence of androphilic male relatives was compared for Samoan gynephilic and androphilic male probands. Samoan androphilic males are known locally as fa'afafine. Compared to Samoan gynephilic males, fa'afafine had significantly more fa'afafine relatives in their maternal and paternal lines. The prevalence of fa'afafine relatives was not significantly different between the paternal and maternal lines for fa'afafine or gynephilic male probands. These findings indicate that male androphilia is familial in Samoa and that it clusters in both the paternal and maternal lines in high fertility populations. We consider our findings in the context of possible explanations for the familial clustering of male androphilia. In addition, we detail how the data presented here illuminate the prevalence of male androphilia in the Samoan population.

Fecundity of paternal and maternal non-parental female relatives of homosexual and heterosexual men

A variety of social, developmental, biological and genetic factors influence sexual orientation in males. Thus, several hypotheses have attempted to explain the sustenance of genetic factors that influence male homosexuality, despite decreased fecundity within the homosexuals. Kin selection, the existence of maternal effects and two forms of balancing selection, sexually antagonistic selection and overdominance, have been proposed as compensatory mechanisms for reduced homosexual fecundity. Here, we suggest that the empirical support for kin selection and maternal effects cannot account for the low universal frequency and stability of the distribution of homosexuals. To identify the responsible compensatory mechanism, we analyzed fecundity in 2,100 European female relatives, i.e., aunts and grandmothers, of either homosexual or heterosexual probands who were matched in terms of age, culture and sampling strategy. Female relatives were chosen to avoid the sampling bias of the fraternal birth order effect, which occurs when indirectly sampling mothers though their homosexual sons. We observed that the maternal aunts and grandmothers of homosexual probands were significantly more fecund compared with the maternal aunts and maternal grandmothers of the heterosexual probands. No difference in fecundity was observed in the paternal female lines (grandmothers or aunts) from either of the two proband groups. Moreover, due to the selective increase in maternal female fecundity, the total female fecundity was significantly higher in homosexual than heterosexual probands, thus compensating for the reduced fecundity of homosexuals. Altogether, these data support an X-linked multi-locus sexually antagonistic hypothesis rather than an autosomal multi-locus overdominance hypothesis.

Constraints on the coevolution of contemporary human males and females

Because autosomal genes in sexually reproducing organisms spend on average half their time in each sex, and because the traits that they influence encounter different selection pressures in males and females, the evolutionary responses of one sex are constrained by processes occurring in the other sex. Although intralocus sexual conflict can restrict sexes from reaching their phenotypic optima, no direct evidence currently supports its operation in humans. Here, we show that the pattern of multivariate selection acting on human height, weight, blood pressure and glucose, total cholesterol, and age at first birth differs significantly between males and females, and that the angles between male and female linear (77.8 ± 20.5°) and nonlinear (99.1 ± 25.9°) selection gradients were closer to orthogonal than zero, confirming the presence of sexually antagonistic selection. We also found evidence for intralocus sexual conflict demonstrated by significant changes in the predicted male and female responses to selection of individual traits when cross-sex genetic covariances were included and a significant reduction in the angle between male- and female-predicted responses when cross-sex covariances were included (16.9 ± 15.7°), compared with when they were excluded (87.9 ± 31.6°). We conclude that intralocus sexual conflict constrains the joint evolutionary responses of the two sexes in a contemporary human population.