Commentary on "A Life History Approach to the Female Sexual Orientation Spectrum"

This blogpost was written prior to having read Severi Luoto's more recent papers, where he updates his position on the female sexual orientation spectrum. Rather than reading this blogpost, I recommend reading my Commentary on Luoto & Rantala's (2022) "Female Bisexuality". There isn't much value in reading this blogpost on its own, but I leave it here for reference.

Recently, I reviewed Luoto et al.'s (2019) "A life history approach to the female sexual orientation spectrum: Evolution, development, causal mechanisms, and health." The authors propose an evolutionary basis for the "various phenotypes in the female sexual orientation spectrum," arguing that female nonheterosexuality emerges as a result of hormonally-mediated Fast Life History strategy and other ultimate-level explanations. Throughout the article, the authors emphasize the existence of different phenotypes of female nonheterosexuality, as described in the graphic shown below. 

The existence of the various phenotypes in the female sexual orientation spectrum has also mostly been overlooked...Since butches and femmes form phenotypically discrete categories, studies on female nonheterosexuality should always seek to ascertain the proportion of subjects identifying as butch/femme so that the results are not confounded by conflating very different types of nonheterosexual subjects...In addition, it should be established whether subjects behave bisexually, in an exclusively homosexual way, or whether they are "mostly heterosexuals".

The authors note a correlation between female masculinity and female homosexuality, describing a spectrum with "incrementally more masculine and homosexual" on one side, less masculine and homosexual on the other. The authors hypothesize that "discrete proximate mechanisms lead to the development of butches and femmes". 

The most complete form of female nonheterosexuality is described as "highly masculinized, exclusively homosexual butch" (butch lesbian) phenotype, which is theorized to result from high prenatal androgens ("androgenic pathway"): "Because of more global masculinizing effects of T, the fetus also develops a more masculine brain in general than heterosexual women, more masculine body, morphology, and exclusive or near-exclusive homosexual orientation." The existence of this phenotype might be because Fast Life History strategy "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."

The femme phenotype is theorized to result from high prenatal estrogen levels ("estrogenic pathway"): "Alternatively, if a female human fetus is exposed to high prenatal estrogen levels at a critical point during neurodevelopment, a male-type (large) INAH3 develops, leading to femme phenotypes of various degrees of same-sex attractions but with a more feminine body morphology than in butch lesbians because of lower androgenic action." The authors hypothesize that maternal stress might contribute to female nonheterosexuality: "Notably, heightened maternal stress may lead to increased estrogen in fetal blood because its production occurs via adrenocorticotropin (ACTH) secretion by the fetal pituitary...Heightened bioavailability of estrogen may constitute a mechanism that links maternal stress to the development of same-sex sexual preferences in offspring..." While the femme phenotype includes homosexuals and bisexuals, butch bisexuals are omitted from this schema.

The authors then describe different ultimate levels of causation, which may interact to form an evolutionary basis for female nonheterosexuality:

As indicated by the radius of each circle, the top four ultimate-level explanations are:

1. Sexually antagonistic selection: "Sexually antagonistic selection arises from the fact that the attributes favored in one sex are sometimes diametrically opposed to those favored in the other sex."
2. Hormonally-mediated Fast Life History strategy: "This is because of the central link that sex hormones create between the development of sexual orientation...and the calibration of life history evolution...Life history strategies are a composite of developmental and psychological variables commonly represented on a fast-to-slow continuum: the fast end is occupied by species/individuals that mature quickly, reproduce early, and focus on quantity rather than quality...Ipso facto, male LH strategies are typically "faster" than those of females...This difference is largely mediated by testosterone (T)."
3. Balanced polymorphism of masculinity: "Since masculinity is deemed to be a polygenic trait, higher masculinity is caused by a greater number of masculinity-inducing alleles and masculinizing environmental factors. If sufficiently masculinized, women's psychological mechanisms that deal with male choice also become masculine, leading to the development of exclusively homosexual orientation in adulthood. However...possessing only some of the masculinizing alleles would in fact be beneficial for the female both in intersexual selection and in intrasexual competition...if possessing them does not entail exclusive homosexuality. According to this hypothesis, greater masculinity could lead to enhanced male acquisition for the "tomboy" due to a reduced psychological gap between the sexes and the consequently enlarged pool of shared interests that a masculine woman would, in theory, have with men."
4. Alloparenting: "In the evolutionary history of the human species, a woman may have been left to raise her offspring alone if the father of her children died or deserted her in search of new mating opportunities. Left alone to take care of offspring in a harsh environment, it would have been more beneficial for a woman to form a relationship with another woman than raise her children entirely alone...In a situation such as this, women with a more malleable sexual orientation may have had an advantage over women with fixed, exclusively heterosexual behavior."

Future Research would benefit from examining studies on female-to-male transsexuals. In general, elevated rates of nonheterosexuality are reported among FTMs. Homosexual FTMs are not a distinct phenotype but a different outcome of the butch lesbian phenotype. Research on female-to-male transsexuals is likely applicable to the Female Sexual Orientation Spectrum. 

The article is an interesting read, but upon reflection there are several points I don't necessarily agree with. 

I. The Sexual Malleability of Exclusively Homosexual Women 

Luoto et al. (2019) make a claim that is not entirely correct, where they assert that "exclusively homosexual women...show male-typical sex-specific arousal patterns and seem to lack the psychophysiological capacity for sexual malleability." 

Chivers, Seto, & Blanchard (2007) found that "a category-specific pattern of genital response can be observed in women, but only among those who report a predominantly or exclusively homosexual orientation and only when they are presented with sexual stimuli that are less intense or explicit (nude figures or solitary figures masturbating)." When presented with more intense stimuli (male-male intercourse), physiological arousal becomes less category-specific, although more male-typical than female controls. Although lesbians display more category-specific arousal patterns, they do so "less robustly than typically reported for men". It is more accurate to describe lesbian sexuality in the following terms: 

"...lesbians’ arousal pattern might be viewed as a much-attenuated version of the male pattern (i.e., with highest arousal to stimuli containing the preferred sex)." (Bailey, 2009)

"Homosexual women show a pattern of genital sexual arousal that is slightly category-specific (i.e., they show stronger genital arousal for female than male stimuli), but their genital responses are not as starkly category-specific as men’s." (Bailey et al., 2016)

II. Butches are not always Exclusively Homosexual

According to the authors, there are only four nonheterosexual phenotypes, which are defined as (1) butch lesbians (2) femme lesbians (3) bisexuals (4) mostly heterosexuals. I do not think this schema accounts for the true range of female nonheterosexuality or masculinity, specifically when it comes to butch sexuality.

Luoto et al. (2019) assume the following is true of butches: "The majority of masculine lesbians [butches] experience stronger attraction to femmes than to one another...Almost all butch lesbians see themselves as exclusively homosexual, whereas about half of femmes categorize themselves as bisexual..." They leave no room for butch bisexuals or butch-attracted butches ("butch4butch"). 

Here, a pitfall is the reliance on self-report. Luoto et al. (2019) fail to account for the tendency of some butch-presenting women to downplay their attraction to men. Self-reported shifts in sexual attractions were described in a sample of 503 female-to-male transsexuals. Of the 273 FTMs who were reported exclusive attraction to women prior to transition, only 124 (45%) reported the same after transition. 133 (49%) reported bisexual attraction after transition, while 16 (6%) reported exclusive attraction to men.

"In the present study, 40% of participants who had transitioned reported a shift in their sexual attraction and these shifts were significantly associated with testosterone use. However, further examination of predictors of sexual attraction shifts revealed that once we accounted for pre-transition sexual attraction, testosterone use was no longer predictive of a shift. Specifically, those FTMs who were AW [attracted to women] pre-transition were most likely to report a change in their sexual attraction, regardless of testosterone use."

These FTMs would have presented as "butch lesbians" prior to transition, in spite of their attraction to men. The following quote from Autoheterosexual is illustrative:

"It was only as I began to live as a man that I realized my attractions toward other men. Prior to that, I firmly denied any trace of attraction to anything but women. I think I feared that attractions to men would make me less of a man."

It is also a less common but well-known phenomenon that some butches are attracted to other butches. This is called "butch4butch". The tom-dee culture of Thailand has a sophisticated classification system of female nonheterosexuality which I think is more reflective of reality. "Toms" (counterpart of butch) attracted to other "toms" are called "tom gay," which is recognized as a distinct category from true "tom". Although they both present as "butch", butch4butch might not be the same phenotype as butch lesbian. The former might be "pseudobutch" while the latter is "true butch".

Discussions of butch nonhomosexuality can be extended to heterosexuals. In his research on female-to-male transsexuality, Phil Illy observes the following pattern of sexual orientation shift:

(1) lesbian/bi woman → (2) trans man → (3) gay/bi trans man

Luoto et al.'s (2019) description of "balanced polymorphism" applies to heterosexual "tomboys". Although research on the brains of transsexuals has failed to find evidence of "masculine brains" in androphilic FTMs, autohomoerotic FTMs might be subtly masculinized in category-specificity of sexuality and a preference to mount ("top") during sex. Additionally, autoandrophilia is associated with autism in females, which might indicate masculinization of cognitive traits. 

Who are butch bisexuals? Who are butch4butch lesbians, and who are butch heterosexuals? Do these belong to their own phenotype(s)? Is there a "pseudobutch" phenotype that is distinct from butch lesbian, and is butchness separable sexual orientation? 

In "Sexual Arousal and Masculinity-Femininity of Women", Rieger et al. (2015) found that lesbians were more "male-typical" in sexual and nonsexual behaviors, but "on average, there were no indications that these 2 patterns were in any way connected." They concluded that "women’s sexual responses and nonsexual traits might be masculinized by independent factors", hypothesizing that "it is possible that androgen influences at different timeframes explain why some women show male-typical sexual arousal and others show male-typical behaviors, but that these are apparently not linked". 

If social environment is not the cause of variations in nonsexual behavior, butchness (female masculinity) could be a distinct spectrum from Kinsey score (sexual orientation), where the former is determined by the dose and timing of androgenic activity, while the latter is determined by masculinization of the INAH3. There is substantial overlap between the two spectra, with the butch lesbian phenotype being the most complete manifestation of both, since the androgenic pathway also masculinizes the INAH3. It could also be the case that different aspects of sexuality (sexual orientation, category-specificity, "top"/"bottom" preference...) are masculinized during different developmental timeframes. 

III. "The Estrogenic Pathway" for Femme Lesbians

I am also not sure whether the specifics of the "estrogenic pathway" outlined for the femme phenotype are entirely correct. Leading up to their "Hypothesized Proximate Mechanism for the Femme Phenotype", Luoto et al. (2019) cite research on female rats: "Research in rodents has shown that it is not T that masculinizes the area in the brain that influences sexual behavior and orientation. Instead, aromatase converts T to estrogen." However, Wallen (2022) notes that rats are an altricial species (born underdeveloped), while humans are a precocial species (born relatively developed): "...altricial rat and mouse models of sexual differentiation may not apply to precocial humans as they appear to use different hormonal mechanisms to produce behavioral sexual differentiation than is the case in precocial species." Wallen (2022) also notes that in rhesus monkeys (a precocial species), "estrogenic metabolites of androgens do not appear to play a role in behavioral sexual differentiation."

As I am not an expert, I don't know if altricial rats or precocial rhesus monkeys are a better model for the development of sexual orientation and sex-typed behaviors in humans.

Related Blog Posts

Commentary on Luoto & Rantala's (2022) Female Bisexuality

Commentary Apostolou (2022) "The Evolution of Female Same-Sex Attraction"

Severi Luoto vs. Lisa Diamond

References

Bailey, J. M. (2009). What is sexual orientation and do women have one?. In Contemporary perspectives on lesbian, gay, and bisexual identities (pp. 43-63). New York, NY: Springer New York. https://doi.org/10.1007/978-0-387-09556-1_3

Bailey, J. M., Vasey, P. L., Diamond, L. M., Breedlove, S. M., Vilain, E., & Epprecht, M. (2016). Sexual Orientation, Controversy, and Science. Psychological Science in the Public Interest, 17(2), 45-101. https://doi.org/10.1177/1529100616637616 (Original work published 2016)

Chivers, M. L., Seto, M. C., & Blanchard, R. (2007). Gender and sexual orientation differences in sexual response to sexual activities versus gender of actors in sexual films. Journal of personality and social psychology, 93(6), 1108. https://doi.org/10.1037/0022-3514.93.6.1108

Chivers, M. L. (2017). The specificity of women’s sexual response and its relationship with sexual orientations: A review and ten hypotheses. Archives of Sexual Behavior, 46(5), 1161-1179. https://doi.org/10.1007/s10508-016-0897-x

Illy, P. (2023). Autoheterosexual: Attracted to being the other sex. Houndstooth Press.

James, S. E., Herman, J. L., Rankin, S., Keisling, M., Mottet, L., & Anafi, M. (2016). The Report of the 2015 U.S. Transgender Survey. Washington, DC: National Center for Transgender Equality. https://transequality.org/sites/default/files/docs/usts/USTS-Full-Report-Dec17.pdf 

Luoto, S., Krams, I., & Rantala, M. J. (2019). A life history approach to the female sexual orientation spectrum: Evolution, development, causal mechanisms, and health. Archives of sexual behavior, 48(5), 1273-1308. https://doi.org/10.1007/s10508-018-1261-0

Meier, S. C., Pardo, S. T., Labuski, C., & Babcock, J. (2013). Measures of clinical health among female-to-male transgender persons as a function of sexual orientation. Archives of Sexual Behavior, 42(3), 463-474. https://doi.org/10.1007/s10508-012-0052-2

Raines, J., Holmes, L., Watts-Overall, T. M., Slettevold, E., Gruia, D. C., Orbell, S., & Rieger, G. (2021). Patterns of genital sexual arousal in transgender men. Psychological Science, 32(4), 485-495. https://doi.org/10.1177/0956797620971654 

Rieger, G., Savin-Williams, R. C., Chivers, M. L., & Bailey, J. M. (2016). Sexual arousal and masculinity-femininity of women. Journal of Personality and Social Psychology, 111(2), 265–283. https://doi.org/10.1037/pspp0000077

Sinnott, M. (2012). Korean-pop, tom gay kings, les queens and the capitalist transformation of sex/gender categories in Thailand. Asian Studies Review, 36(4), 453-474. https://doi.org/10.1080/10357823.2012.739995

Wallen, K., Faykoo-Martinez, M., & Holmes, M. M. (2022). Prenatal steroid hormones and sex differences in juvenile rhesus macaque behavior. In Gender and sexuality development: Contemporary theory and research (pp. 39-72). Cham: Springer International Publishing. https://doi.org/10.1007/978-3-030-84273-4_2