Possible Balancing Selection in Human Female Homosexuality

Ciani, Andrea; Battaglia, Umberto; Cesare, Linda; Ciani, Giorgia Camperio; Capiluppi, Claudio

doi:10.1007/s12110-017-9309-8

Cited by 26 publications

(8 citation statements)

References 77 publications

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“…Those nonheterosexual individuals (both men and women) with a greater proportion of samesex partners had a larger reproductive disadvantage (lower birth-year adjusted number of children) relative to exclusively heterosexual participants (Ganna et al, 2019). However, this fitness impairment may be offset by the reported higher number of offspring in nonheterosexual women's kin compared with the kin of heterosexual women (Camperio Ciani, Battaglia, Cesare, Camperio Ciani, & Capiluppi, 2018), indicating sexually antagonistic selection (Luoto et al, 2019a). Sexually antagonistic selection refers to the fact that the attributes favored in one sex are sometimes opposed to those favored in the other sex, which may lead to a fitness detriment when the genotype results in offspring of one sex and a fitness increase when it results in offspring of the other sex (Luoto et al, 2019a).…”

Section: Gwas: Same-sex Sexual Behaviormentioning

confidence: 93%

Behavioral genetics

Luoto¹,

Menie²

2021

Preprint

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In this introductory chapter, we discuss the nexus between evolutionary theory and behavioral genetics, using it to elucidate the biological origins of human behavior and motivational predispositions. We introduce relevant behavioral genetics methods and evolutionary theoretical background to provide readers with the necessary conceptual tools to deepen their engagement with evolutionary behavioral genetics—as well as to help them take on the challenge of building a scientifically and evolutionarily more consilient account of human behavior. To demonstrate the utility of behavioral genetics in evolutionary behavioral science, our analytical examples range from personality, cognition, and sexual orientation to pair-bonding. We conclude by presenting a few recent landmark studies in behavioral genetics research with a particular focus on two aspects of sexual behavior: assortative mating and same-sex sexual behavior. This chapter considers behavioral genetics methods and their connection with evolutionary science more broadly while providing a succinct overview of recent advances in understanding the evolutionary genetic underpinnings of human sexual behavior, mate choice, and basic motivational processes. It is a sine qua non of scientifically principled evolutionary behavioral scientists to acknowledge the distal evolutionary and proximal genetic processes which, interlinked, underlie the psychobehavioral predispositions that form the variegated fabric of human societies and, more broadly, the diversity of life found in nature. These evolutionary processes operate from distal selection pressures acting on genetic material through hundreds of millions of years of natural selection—and from individual and population differences in genotypes to their manifestations in complex behavioral phenotypes and life outcomes in contemporary humans—which, in turn, enact concomitant selection pressures on the genetic material underlying and arising from them.

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Section: Gwas: Same-sex Sexual Behaviormentioning

confidence: 93%

Behavioral genetics

Luoto¹,

Menie²

2021

Preprint

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“…This advantage to the male may be sufficiently large to offset the potential cost of the alleles when they occur in the exclusively homosexual female phenotype (Luoto et al, 2019a). Some evidence for this hypothesis-known as sexually antagonistic selection-has been provided in Italian (Camperio Ciani, Battaglia, Cesare, Camperio Ciani, & Capiluppi, 2018) and Australian samples (Sabia, Wooden, & Nguyen, 2017), where the reproductive success of nonheterosexual women was lower than that of heterosexual women. However, this fitness detriment can be offset by a higher number of offspring in nonheterosexual women's kin compared with the kin of heterosexual women, as reported in the Italian sample (Camperio Ciani et al, 2018).…”

Section: Sexually Antagonistic Selectionmentioning

confidence: 99%

“…Some evidence for this hypothesis-known as sexually antagonistic selection-has been provided in Italian (Camperio Ciani, Battaglia, Cesare, Camperio Ciani, & Capiluppi, 2018) and Australian samples (Sabia, Wooden, & Nguyen, 2017), where the reproductive success of nonheterosexual women was lower than that of heterosexual women. However, this fitness detriment can be offset by a higher number of offspring in nonheterosexual women's kin compared with the kin of heterosexual women, as reported in the Italian sample (Camperio Ciani et al, 2018). Indirect support for the sexually antagonistic selection hypothesis has been recorded in nonhuman animals.…”

Section: Sexually Antagonistic Selectionmentioning

confidence: 99%

Female bisexuality

Luoto¹,

Rantala²

2020

Preprint

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Bisexual behavior is an order of magnitude more common than exclusive homosexuality in women. Many evolutionary hypotheses on sexual orientation have focused on homosexuality, particularly in men, yet there has recently been a growing recognition that male and female homosexuality may have different evolutionary origins, and that the various forms of nonheterosexuality in the female sexual orientation spectrum may arise via discrete evolutionary–developmental mechanisms. Evolutionarily informed sex research therefore has the fascinating task of understanding the whole spectrum of female sexual orientation—from heterosexual, mostly heterosexual, and bisexual women through to exclusively homosexual women, and from feminine femmes to masculine butches—including the proximate mechanisms and ultimate functions that underlie that variation. Here, we address that task by applying Tinbergen’s four questions to analyze female bisexuality, synthesizing existing research on proximate mechanisms, ontogeny, phylogeny, and ultimate functions. Research in psychology and behavioral sciences indicates that bisexual women comprise a group distinct from heterosexual women and, on some metrics, even from lesbian women: bisexual women have more male-typical personality traits, more unrestricted sociosexual attitudes and behaviors, higher sexual responsiveness, earlier reproduction, higher substance use, higher incarceration rates, and worse health outcomes than heterosexual women. There is broad evidence from across mammalian species which indicates that individual differences in prenatal exposure to sex hormones creates individual differences in brain morphology, cognition, behavioral predispositions, and even life outcomes. They are typically studied in a sex differences framework, but there is now enough evidence to suggest that sexual orientation differences along these parameters can also be robust and informative. We review 10 ultimate-level hypotheses on the evolution of female bisexuality and conclude that four hypotheses—balanced polymorphism of masculinity, sexually antagonistic selection, hormonally mediated fast life history strategy, and byproduct—are currently best supported by evidence. These hypotheses are also consilient with the wealth of neurodevelopmental evidence on the masculinization of the brain and behavior which is thought to underlie variation in female sexual orientation. By synthesizing ultimate functions with proximate mechanisms—combined with powerful mid-level frameworks such as life history theory—evolutionary scientists are in a stronger position to provide a comprehensive account of the phenotypic variation observed in the female sexual orientation spectrum.

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“…The logic of the SAGH can be in principle applied also to female homosexuality (Luoto et al, 2019 ). Camperio Ciani et al ( 2018 ) found that the pedigree size and kin fertility of lesbian women were significantly higher than in straight women. If sexually antagonistic selection were responsible for maintaining female homosexuality-associated alleles, we should see increased fertility in lesbian women’s male relatives.…”

Section: Introductionmentioning

confidence: 99%

Fertility of Czech Gay and Straight Men, Women, and Their Relatives: Testing the Sexually Antagonistic Gene Hypothesis

Fořt,

Flegr,

Kuba

et al. 2024

Arch Sex Behav

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One proposal for the persistence of homosexuality in the human population is the sexually antagonistic gene hypothesis, which suggests that the lower fertility of homosexual individuals, especially men, may be compensated by higher fertility of their relatives of the opposite sex. To test this hypothesis, we have collected data from 7,312 heterosexual men, 459 gay men, 3,352 heterosexual women, and 79 lesbian women mainly from Czechia. In an online survey, participants answered questions regarding their own as well as their parents’ and grandparents’ fertility. For men, we obtained no significant results except for higher fertility of gay men’s paternal grandmothers, but the magnitude of this effect was very small. For the female sample, we recorded lower fertility of lesbian women’s mothers and fathers. In line with our expectations, both gay men and lesbian women had lower fertility rates than their heterosexual counterparts. Our results are consistent with recent studies which likewise do not support the sexually antagonistic gene hypothesis.

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Possible Balancing Selection in Human Female Homosexuality

Cited by 26 publications

References 77 publications

Behavioral genetics

Behavioral genetics

Female bisexuality

Fertility of Czech Gay and Straight Men, Women, and Their Relatives: Testing the Sexually Antagonistic Gene Hypothesis

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