The dual control model, first articulated by Erick Janssen and John Bancroft, conceptualizes sexual response as the product of two interacting neurophysiological systems: a sexual excitation system that promotes arousal and desire in response to appropriate stimuli, and a sexual inhibition system that suppresses response in the presence of threat or perceived risk. In this framework, inhibition itself is not a single entity but comprises distinct factors, including inhibitory cognitions—worries, distractions, and catastrophic thoughts about performance or consequences—and inhibition related to performance failure. Excitation, too, is multifactorial, encompassing the ease with which sexual cues generate arousal. The model has proven remarkably useful for understanding individual differences in sexual risk-taking, arousal, and dysfunction, but until now it had not been systematically applied to sexual aversion.

Sexual aversion is defined as extreme aversion to partnered genital sexual contact. It has a long and somewhat turbulent history in psychiatric classification. First described in the clinical literature in the late 1970s and 1980s, sexual aversion disorder was included in the DSM-IV but was subsequently excluded from the DSM-5, with commentators arguing that its symptoms overlapped with other conditions such as specific phobias, panic disorder, and other sexual dysfunctions. Yet researchers have continued to insist on its clinical relevance, noting that aversion appears as a trans-diagnostic symptom across multiple sexual disorders and causes profound suffering in those who experience it. Recent population-based work from Canada has suggested that aversion is not rare, lending urgency to efforts to understand what distinguishes it from superficially similar presentations.

The conceptual puzzle is genuine. Sexual aversion shares behavioral features with asexuality—both involve avoidance of sexual behavior—and both are associated with sexual disgust. But the two diverge sharply on one crucial dimension: distress. For asexual individuals, the absence of sexual attraction or interest is not, in itself, a source of suffering; indeed, many asexual people describe their orientation as a stable identity rather than a problem to be solved. Sexual aversion, by contrast, provokes significant distress. Aversion also shares features with low sexual desire, including avoidance and distress, but the precise relationship between aversion and diminished desire had never been formally established. The Canadian team, led by Nahanni Musiani and senior author Lori Brotto, hypothesized that the dual control model could untangle these threads: if aversion is driven by heightened inhibition, it should be statistically separable from low desire and asexuality, which they predicted would instead be associated with diminished excitation.

To test this, the researchers recruited 2,065 participants who completed a battery of validated self-report questionnaires measuring sexual aversion, sexual desire, asexuality, sexual distress, and the excitation and inhibition factors of the dual control model. Sexual aversion was assessed with instruments developed for that purpose, desire with the Sexual Desire Inventory, and asexual identification with the Asexuality Identification Scale, a measure developed by the same research group. Sexual distress was captured with distress scales validated across genders. The analytic strategy was straightforward and transparent: Pearson correlations were used to map the relationships among variables, and multiple regression models tested which excitation and inhibition factors uniquely predicted aversion, desire, and asexuality. Secondary analyses examined gender differences across the sample.

The results were striking in their clarity. Sexual aversion, asexuality, and low desire were indeed correlated with one another—consistent with their shared surface features—but the correlations were generally modest. Only one association reached moderate strength: the relationship between sexual aversion and sexual distress. This single finding carries enormous conceptual weight, because it confirms empirically what clinicians have long observed anecdotally: distress, not the absence of sex itself, is the signature of aversion. A person can experience little desire or little attraction without suffering; what distinguishes the person with aversion is that contact with sexuality triggers a response they experience as unbearable, and that experience hurts.

The regression analyses went further, revealing that the three outcomes are predicted by different profiles within the dual control model. Sexual aversion was significantly predicted by sexual inhibition—particularly inhibitory cognitions. In other words, the people most prone to aversion were those whose minds generate potent, intrusive, suppressive thoughts in sexual contexts. This is a fundamentally inhibitory profile: the excitation system may be intact, but the braking system is locked. Asexuality, by contrast, was predicted by reduced sexual excitation, with only a weak contribution from increased inhibition. Low sexual desire showed the mirror image: it was predicted by high excitation working in the opposite direction—specifically, low excitation scores predicted low desire—along with a weak role for reduced inhibition. The pattern supports the team’s core hypothesis: aversion is a disorder of excessive braking, whereas asexuality and low desire reflect a quieter accelerator.

The distinction is not merely academic. If aversion is driven by inhibitory cognitions, then treatments should target those cognitions directly. The authors suggest that interventions focusing on sexual inhibition—particularly the cognitive component—may be a promising therapeutic avenue for sexual aversion, an area where evidence-based treatments remain scarce. This aligns with a broader literature showing that cognitive behavioral therapy and mindfulness-based approaches can reduce sexual distress and improve outcomes across sexual dysfunctions, likely in part by modifying the attentional and interpretive processes that fuel inhibition. For clinicians, the message is that a patient presenting with sexual avoidance should not be lumped into a generic category of low libido; assessing the excitation–inhibition profile could determine which treatment pathway is appropriate.

The study also contributes to an ongoing scientific and cultural conversation about asexuality. Research over the past two decades has established that asexuality is a distinct and stable orientation rather than a symptom of disorder, and the new findings reinforce that position in mechanistic terms: asexuality looks like diminished excitation and is not characterized by the pathological inhibition profile seen in aversion. Notably, the study was designed with input from the Asexuality Research Advisory Board, reflecting growing efforts to conduct this research collaboratively with the ace community. Funded by a Discovery Grant from the Natural Sciences and Engineering Research Council of Canada and approved by the University of British Columbia’s Behavioral Research Ethics Board, the study exemplifies how large-sample, theory-driven research can resolve classification disputes that have persisted since sexual aversion disorder was first codified. The dual control model, introduced to explain the psychophysiology of arousal, has now proven equally powerful for explaining its absence—and, crucially, for explaining why one form of absence causes suffering while another does not. The findings suggest a future in which sexual avoidance is diagnosed not by behavior alone but by the underlying balance of excitation, inhibition, and distress that produces it.

Subject of Research: Predicting sexual aversion, low sexual desire, and asexuality using the dual control model of sexual response.

Article Title: Predicting Sexual Aversion, Low Sexual Desire, and Asexuality Using the Dual Control Model

Article References: Musiani, N., Zdaniuk, B., Milani, S., Makarenko, B., & Brotto, L. A. (2026). Predicting Sexual Aversion, Low Sexual Desire, and Asexuality Using the Dual Control Model. Archives of Sexual Behavior. https://doi.org/10.1007/s10508-026-03529-8

Image Credits: AI Generated

DOI: 10.1007/s10508-026-03529-8

Keywords: sexual aversion, asexuality, low sexual desire, dual control model, sexual inhibition, sexual excitation, sexual distress, DSM-5, sexual dysfunction, Archives of Sexual Behavior, inhibitory cognitions, sex research

The study was conducted by Jakub Fořt of Charles University in Prague, who analyzed data from an online survey of 3,963 respondents collected between June 2020 and March 2021 in Czechia and Slovakia. After a series of careful exclusions—removing participants who did not report their sex, were under 18 or over 79, were adopted or unsure about it, identified as transgender, or were classified as homosexual—the final sample comprised 843 heterosexual men, 184 bisexual men, 58 asexual men, 331 heterosexual women, 248 bisexual women, and 32 asexual women. Sexual orientation was assessed using five Kinsey-like items covering self-identification, fantasies, desires, and the sex of sexual partners over the past year and past five years, while asexuality was determined by self-identification alone.

The fraternal birth order effect was first documented by Ray Blanchard and Anthony Bogaert in 1996, and it has since been replicated by numerous research teams across different geographic regions, including in a very large dataset drawn from Dutch population-level administrative records. Meta-analyses have confirmed the pattern: each additional older brother increases the odds of male homosexuality by a modest but reliable margin. Crucially, the effect appears to depend on maternal siblings—boys who share a biological mother with their older brothers—rather than on adopted or stepbrothers, which points strongly toward a biological mechanism operating during pregnancy rather than a social or rearing influence.

The leading explanation is the maternal immune hypothesis. According to this framework, male fetuses carry proteins that are foreign to the mother’s immune system, most notably male-specific, Y-linked antigens. With each pregnancy carrying a male fetus, the mother’s immune system is progressively sensitized and produces antibodies against these antigens. In subsequent pregnancies, these antibodies can cross the placenta and may alter the sexual differentiation of the developing brain in ways that increase the likelihood of same-sex attraction in adulthood. The hypothesis received a major boost in 2018, when a laboratory study reported that mothers of gay men had elevated blood levels of antibodies against neuroligin 4 Y-linked, or NLGN4Y, a male-specific protein, compared with mothers of heterosexual men.

A complementary line of thinking involves fetal microchimerism, the phenomenon by which fetal cells cross the placenta, engraft in maternal tissues, and persist in the mother’s body for decades after birth. Male fetal progenitor cells have been detected in maternal blood as long as 27 years postpartum. These engrafted cells could, in principle, influence maternal physiology during later pregnancies or contribute to a sustained production of antibodies, providing a plausible route through which the birth order effect could operate. The two mechanisms are not mutually exclusive, and researchers note that both remain active areas of investigation.

In the new study, Fořt employed modern statistical methods designed to disentangle the fraternal birth order effect from a separate phenomenon known as the female fecundity effect, in which mothers of gay men have been reported to have more children overall. Because larger sibships mechanically increase the probability of having more older brothers and sisters, conflating the two effects has been a persistent methodological problem. The analysis therefore used two logistic regression parameterizations—one treating sibship size, number of older siblings, older brothers, and younger brothers as predictors, and a parallel version substituting older and younger sisters—while controlling for the participant’s age and the mother’s age at the participant’s birth to account for birth cohort effects. The study also verified that sibling sex ratios in the heterosexual reference groups did not deviate from the expected population value of 106 boys per 100 girls, guarding against distortions from parental stopping rules.

The headline result was clear: the number of older siblings significantly increased the odds of bisexuality in men, with an odds ratio of 1.66, meaning each additional older sibling raised the probability of male bisexuality by roughly two-thirds. Notably, this effect size is almost identical to that previously found for homosexual men in the same Czech and Slovak sample, and it is somewhat larger than earlier meta-analytic estimates for gay men drawn from convenience and probability samples. No statistically significant effects emerged for bisexual women, asexual men, or asexual women, and no significant sororal birth order effect—concerning older sisters—or sibling size effects were detected in any group.

Yet the pattern of non-significant results was itself intriguing. For bisexual women, asexual men, and asexual women, the estimated fraternal birth order effect pointed in the same direction and was of a magnitude broadly similar to that observed in bisexual men, with odds ratios of 1.46, 1.70, and 1.62 respectively. The failure to reach statistical significance likely reflects limited statistical power, particularly given the small numbers of asexual participants—only 58 asexual men and 32 asexual women were included. Post-hoc power analyses indicated acceptable power only for bisexual men, with power falling to 0.68 for bisexual women and just 0.46 for asexual women. The author cautions, therefore, that these findings should be treated as preliminary until larger, more diverse samples are examined.

If the fraternal birth order effect in bisexual men is corroborated by future studies and meta-analyses, the implication would be significant: whatever biological mechanism underlies the effect, it appears to be shared between exclusively and partially same-sex attracted men. In other words, male bisexuality and male homosexuality may share a common biodevelopmental origin, rather than arising through entirely distinct pathways. The author even speculates that the mechanism could extend across mammalian species, noting a recent study in which male laboratory rats born to multiparous mothers showed a greater tendency toward same-sex partner preference—a fraternal birth order-like pattern outside humans.

The findings also contribute to a sparse literature on asexuality, a sexual orientation that has been almost entirely absent from birth order research until recently. Prior evidence has been mixed: an early study suggested asexual men had more older brothers than heterosexual men, but subsequent rigorous analyses found no such effect, and results on sibship size among asexual individuals have been contradictory. One recent study of UK Biobank participants reported smaller sibship sizes for asexual men and women, while another found larger sibships for asexual men and no difference for asexual women. The present study adds another data point, though its own limitations—including the convenience sampling method, the online format, and the modest asexual subsample—mean that definitive conclusions about asexuality and sibling composition remain out of reach for now.

Subject of Research: The fraternal birth order effect and other sibship effects in bisexual and asexual men and women

Article Title: Fraternal Birth Order Effect and Other Sibship Effects in Bisexual and Asexual Men and Women

Article References: Fořt, J. (2026). Fraternal Birth Order Effect and Other Sibship Effects in Bisexual and Asexual Men and Women. Archives of Sexual Behavior. https://doi.org/10.1007/s10508-026-03536-9

Image Credits: AI Generated

DOI: 10.1007/s10508-026-03536-9

Keywords: fraternal birth order effect, sexual orientation, bisexuality, asexuality, maternal immune hypothesis, birth order, sibship size, fetal microchimerism, female fecundity effect, Archives of Sexual Behavior, NLGN4Y, evolutionary biology