Possible evolutionary origins of human female sexual fluidity

Emerging insights into the genetics and evolution of human same-sex sexual behavior

Thanks to twin studies, it has been known for decades that human same-sex sexual behavior (SSB) has a substantial heritable component. However, only recently have large genome-wide association studies (GWAS) begun to illuminate the complex genetics involved. These studies have established that SSB is influenced by many common genetic variants, each with tiny but cumulative effects. The evolutionary explanation for the persistence of genetic variants associated with SSB, despite their apparent fitness costs, remains uncertain. In this review, we synthesize advances in understanding the genetic and evolutionary bases of SSB, while identifying the many areas in which we still have much to learn.

Worldwide study reveals fluid sexual preferences in females and no association between gynephilia and non-heterosexuality

BACKGROUND

Social factors and a lack of clearself-awareness may prevent women from explicitly reporting their non-heterosexuality, and implicit measures could provide more reliable data.

AIM

This study examined non-heterosexuality and gynephilia in a large, global sample of women using implicit and explicit methods.

METHODS

A sample of 491 women participated in this cross-sectional study. Participants completed a biographical questionnaire, the Autobiographical-Implicit Association Test, the Sexual Preference-Implicit Association Test (SP-IAT), and an explicit measure of sexual orientation. In a follow-up study, 263 participants were recontacted and completed the Autobiographical Sexual Orientation IAT and answered additional questions about their sexual behavior and preferences related to the stimuli on the SP-IAT.

OUTCOMES

The main outcome measures were D-scores on implicit association tests and scores on explicit measures of sexual orientation and behaviors.

RESULTS

Implicit measures showed a higher rate of gynephilia (67.8%) than explicit non-heterosexuality (19.6%), with consistent results across continents. The findings suggest that women may be attracted to other women without necessarily desiring sexual encounters with them. Furthermore, the results suggest a degree of fluidity in sexual preferences in the female population.

CLINICAL IMPLICATIONS

Studying the prevalence of gynephilia and non-heterosexuality in adult women can inform the development of health promotion programs tailored to women's diverse sexual experiences and preferences.

STRENGTHS & LIMITATIONS

Strengths include the global sample and the use of both implicit and explicit measures. Limitations involve the cross-sectional web-based design, potential sample biases, and aspects related to the validity of the SP-IAT.

CONCLUSION

Implicit measures of non-heterosexuality appear to be less tied to social factors than explicit assessments. In women, gynephilia may not necessarily serve as a proxy for non-heterosexuality. Moreover, women seem to exhibit greater fluidity in sexual preferences and behaviors than men.

The Direct Reproductive Cost of Same-Sex Attraction: Evidence from Two Nationally Representative U.S. Samples

Same-sex attraction is associated with a direct reproductive cost, i.e., a reduced number of biological children. The current study aimed to assess this cost for different forms of sexual attraction (i.e., only attracted to opposite sex, mostly attracted to opposite sex, equally attracted to both sexes, mostly attracted to same-sex, only attracted to same-sex), using two large nationally representative datasets (N = 15,208) from the USA. The results indicated that same-sex attraction was associated with substantial loss in direct reproductive output. More specifically, significant differences between the different types of same-sex attraction were found: Exclusive and mostly homosexual orientation identities were associated with the highest direct reproductive cost, while mostly attracted to opposite sex orientation and bisexuality identities were associated with lower direct reproductive costs. In addition, bisexual women did not differ significantly from exclusively heterosexual women in terms of their reproductive output. The implications of these findings for the evolutionary origins of same-sex attraction are further discussed.

Infertility and same-sex attraction in women

A polygyny hypothesis of female sexual fluidity proposes that women may have been evolutionarily selected to be sexually fluid, in order to have occasional sex with their cowives in polygynous marriage to reduce tension and conflict inherent in such marriage, while at the same time reproducing children with their husbands. Among others, the hypothesis predicts that women who are biologically (but not surgically) infertile would experience greater same-sex attraction. Biological infertility stems from natural, evolutionarily familiar causes such as menopause, whereas surgical infertility stems from artificial, evolutionarily novel causes such as tubal ligation or hysterectomy. Consistent with the prediction, the analyses of the National Survey of Family Growth data showed that biological infertility, but not surgical infertility, was significantly associated with same-sex self-identified labels, behavior and sexual attraction in women. Biological infertility nearly doubled the odds of women having engaged in same-sex behavior and the number of same-sex partners in the last 12 months and nearly tripled the number of same-sex partners in life. In sharp contrast, biological infertility was not associated (and surgical infertility was significantly negatively associated) with same-sex attraction in men.

Sexual Desire and Fantasies in the LGBT+ Community: a Focus on Bisexuals, Transgender, and Other Shades of the Rainbow

Purpose of Review

The purpose of this review is to summarize the current knowledge on sexual desire expressions, sexual orientation, and identity in understudied groups inside the LGBT+ community.

Recent Findings

Sexual desire and related problems have unique expressions in LGBT+ people which influence their sexual health. Emerging sex-positive approaches might be powerful and prominent tools to provide support and education on behalf of safer sex practices and marginalized sexualities. The importance of deepening LGBT+ sexualities and relationships, not only in lesbian women and gay men but also in all the other shades of the rainbow (bisexual, transgender, asexual, fluid, and non-binary/genderqueer identities), is strongly highlighted.

Summary

A lack of literature regarding sexual desire in LGBT+ people is reported. Results are controversial and research is still limited on this topic, with little information available about sexual and health needs of sexual minorities beyond gay and lesbian people.

Sexual Experimentation in Heterosexual, Bisexual, Lesbian/Gay, and Questioning Adolescents From Ages 11 to 15

To examine adolescent sexuality development, we analyzed data from a British cohort study (N = 5,070), which assessed the same 12-14 sexual activities at ages 11, 12, 13, and 15, and sexual orientation identity at age 15. The sexual activities ranged from low (e.g., cuddling), moderate (e.g., kissing), to high (e.g., sexual intercourse) intensity. We found that most adolescents having sexual activities of low-to-moderate intensity with same-sex individuals also had them with other-sex individuals, and adolescents having other-sex contacts of low intensity often reported them nonexclusively. Furthermore, other-sex and same-sex sexual activities did not reliably distinguish between sexual orientation identities. Sex differences in these phenomena were absent or small. These findings suggest that many adolescents have low-intensity nonexclusive sexual behaviors.

Sexual Orientation Development of Heterosexual, Bisexual, Lesbian, and Gay Individuals: Questions and Hypotheses Based on Kaestle's (2019) Research

Christine Kaestle's work assessed the three major dimensions of sexual orientation: sexual attractions, behaviors, and identity. She tracked the unfolding of sexual orientation over time, from adolescence to early adulthood (i.e., late twenties to early thirties), using three waves of data from the National Longitudinal Study of Adolescent to Adult Health (Add Health), a U.S. representative sample. This article addresses some of the implications, questions, and hypotheses suggested by Kaestle's findings. It ends by requesting follow-up data in adulthood to test hypotheses and resolve differences between the author and Kaestle in interpretation of the data.

A Life History Approach to the Female Sexual Orientation Spectrum: Evolution, Development, Causal Mechanisms, and Health

Women's capacity for sexual fluidity is at least as interesting a phenomenon from the point of view of evolutionary biology and behavioral endocrinology as exclusively homosexual orientation. Evolutionary hypotheses for female nonheterosexuality have failed to fully account for the existence of these different categories of nonheterosexual women, while also overlooking broader data on the causal mechanisms, physiology, ontogeny, and phylogeny of female nonheterosexuality. We review the evolutionary-developmental origins of various phenotypes in the female sexual orientation spectrum using the synergistic approach of Tinbergen's four questions. We also present femme-specific and butch-specific hypotheses at proximate and ultimate levels of analysis. This review article indicates that various nonheterosexual female phenotypes emerge from and contribute to hormonally mediated fast life history strategies. Life history theory provides a biobehavioral explanatory framework for nonheterosexual women's masculinized body morphology, psychological dispositions, and their elevated likelihood of experiencing violence, substance use, obesity, teenage pregnancy, and lower general health. This pattern of life outcomes can create a feedback loop of environmental unpredictability and harshness which destabilizes intrauterine hormonal conditions in mothers, leading to a greater likelihood of fast life history strategies, global health problems, and nonheterosexual preferences in female offspring. We further explore the potential of female nonheterosexuality to function as an alloparental buffer that enables masculinizing alleles to execute their characteristic fast life history strategies as they appear in the female and the male phenotype. Synthesizing life history theory with the female sexual orientation spectrum enriches existing scientific knowledge on the evolutionary-developmental mechanisms of human sex differences.

Father absence, sociosexual orientation, and same-sex sexuality in women and men

A recent evolutionary theory of female sexual fluidity suggests that women may not have sexual orientations in the same sense that men do, and that women's apparent sexual orientation may instead be a byproduct of their sociosexual orientation. One developmental factor that has consistently been shown to influence sociosexual orientation is father absence in childhood. Consistent with the prediction of the theory, the analyses of the National Longitudinal Study of Adolescent to Adult Health (Add Health) data show that father absence significantly increases women's, but not men's, same-sex sexuality in adulthood, whether it is measured by self identity, sexual behaviour, or romantic attraction. Further consistent with the theory, the association between father absence and same-sex sexuality in women is entirely mediated by their sociosexual orientation.

Who Adopts Queer and Pansexual Sexual Identities?

Some nonheterosexual individuals are eschewing lesbian/gay and bisexual identities for queer and pansexual identities. The present study aimed to examine the sexual and demographic characteristics of nonheterosexual individuals who adopt these labels. A convenience sample of 2,220 nonheterosexual (1,459 lesbian/gay, 413 bisexual, 168 queer, 146 pansexual, and 34 other "write-in") individuals were recruited for a cross-sectional online survey. In support of our hypotheses, those adopting pansexual identities were younger than those adopting lesbian, gay, and bisexual identities, and those adopting queer and pansexual identities were more likely to be noncisgender than cisgender, and more likely to be cisgender women than men. The majority of pansexual individuals demonstrated sexual orientation indices within the bisexual range, and showed equivalent patterns of sexual attraction, romantic attraction, sexual behavior, and partner gender as bisexual-identified men and women. In contrast, three-quarters of queer men, and more than half of queer women, reported sexual attraction in the homosexual range. This study found that rather than a general movement toward nontraditional sexual identities, queer and pansexual identities appear most appealing to nonheterosexual women and noncisgender individuals. These findings contribute important information regarding who adopts queer and pansexual identities in contemporary sexual minority populations.