Parental Income and the Sexual Behavior of Their Adult Children: A Trivers–Willard Perspective. John T. Manning, Bernhard Fink, and Robert Trivers. Evolutionary Psychology, December 12, 2022. https://doi.org/10.1177/14747049221142858
Abstract: Parental income is negatively and linearly related to the digit ratio (2D:4D; a proxy for prenatal sex steroids) of their children. Children of parents with high income are thought to be exposed to higher prenatal testosterone and develop lower 2D:4D. It is further hypothesized that 2D:4D relates to sexual orientation, although it is unclear whether the association is linear or curvilinear. Here, we consider patterns of parental income and its association with the sexual behavior of their adult children in a large online study (the BBC internet study). There were curvilinear relationships with parental income in male and female children. The highest frequencies of homosexuality and bisexuality were found in the lowest income group (bottom 25% of the population), the lowest frequencies in the income group representing the upper 50% of the population, and intermediate values in the other groups (low 50% and top 25% of the population). Parental income showed a U-shaped association with scores for same-sex attraction and an inverted U-shaped association with opposite-sex attraction. Thus, for the first time, we show that same-sex attraction is related to parental income. The curvilinear relationship between parental income and sexual behavior in their adult children may result from an association between very high fetal estrogen or testosterone and attraction to partners of the same sex. Among non-heterosexuals, and in both sexes, very high fetal estrogen may be associated with femme or submissive sexual roles, and very high fetal testosterone with butch and assertive sexual roles.
Check also High-income women may prenatally masculinize their sons at the expense of the fitness of their daughters; low-income women may prenatally feminize their daughters at the fitness expense of their sons:
Discussion
The current study found that in male adult children, homosexuality was the most frequent non-heterosexual group and bisexuality was rare. For female adult children, bisexuality was more frequent than homosexuality. Parental income was related to the frequency of sexual orientation (heterosexuality, homosexuality, bisexuality) of their adult children. The association between parental income and sexual orientation of children was found in the total sample and when we considered the most numerous ethnic group (Whites) in the two largest national samples (UK and USA), thus confirming our prediction (i).
Parents with income that was “much lower than others” (bottom 25% of the population) had the highest frequencies of homosexuality and bisexuality for both male and female adult children. The lowest frequency of homosexuality was found in the male and female children of parents with an income “slightly higher than others” (upper 50% of the population). Parents with an income “much higher than others” (top 25% of the population) had male and female children with intermediate frequencies of homosexuality.
Concerning adult children's scores for sexual attraction to others, in men, same-sex attraction was highest among children of parents with an income corresponding to the bottom and top 25% of the population, and the lowest scores were found in children of parents with an income “slightly higher than others” (upper 50% of the population). For women, same-sex attraction was greatest for adult children of parents with an “income much lower than others” (bottom 25% of the population), lowest in children of parents with an income “slightly higher than others” (as for men) and intermediate for children of parents with an income representing the top 25% of the population. Splitting the sample for ethnicity (Whites only) and nation (UK and USA), UK scores for adult children's same-sex attraction were lower than those for the US with the former reporting the highest scores for the income group representing the bottom 25% of the population and the latter reporting very high scores for the highest income group (top 25% of the population). Overall, for both the frequency of sexual orientation groups and the same-sex attraction scores, we found no evidence for linear relationships. Concerning same-sex attraction scores, post hoc tests confirmed a U-shaped association such that the frequency of homosexuality/bisexuality and the magnitude of same-sex attraction scores were highest in the adult children from parents with the lowest (bottom 25% of the population) and to a lesser extent in parents with the highest income (top 25% of the population). The nadir of the attraction scores was observed in adult children from parents with an income “slightly higher than others” (upper 50% of the population). Therefore, our prediction (ii) was rejected and prediction (iii) was supported.
The curvilinear relationships between parental income and the sexual behavior of their adult children are, to our knowledge, novel. Our interpretation of these relationships is through the lens of the “Trivers–Willard” hypothesis (
Trivers & Willard, 1973). We suggest that parental income is a marker of maternal condition (
Babones, 2008;
Pickett & Wilkinson, 2015). Male children have a greater variance in reproductive success than female children in human and nonhuman animals (
Bateman, 1948;
Trivers & Willard, 1973). Male children of mothers in poor condition (lowest parental income) will have below-average male reproductive success, but in contrast, daughters from mothers with the lowest parental income will have reproductive success closer to the female mean. Thus, mothers will be selected to favor their daughters depending on parental income by reducing their prenatal testosterone and increasing their prenatal estrogen. If mothers cannot distinguish between their male and female fetuses this will mean they expose their male offspring to a feminized fetal environment. Conversely, mothers in good condition (highest parental income) will androgenize their fetuses of both sexes. We have found high frequencies of homosexuality and bisexuality and same-sex attraction scores in adult children of mothers with the lowest and highest parental income. This suggests that both a high fetal estrogen-to-testosterone ratio and a high fetal testosterone-to-estrogen ratio are related to an increase in the probability of non-heterosexuality in adult children. We speculate that among the former, there may be a high proportion of “receptive” male homosexuals and “femme” female homosexuals. Among the latter, there may be a preponderance of “insertive” male homosexuals and “butch” female homosexuals.
In conclusion, the current study builds on the finding that parental income is negatively related to 2D:4D in both adult female and male children (Manning et al., 2022). Insofar as 2D:4D is a correlate of prenatal sex steroids and prenatal sex steroids influence sexual behavior, we predicted that parental income would be associated with children's sexual orientation and same-sex scores for sexual attraction to others. Our prediction was confirmed, so that compared to adult children of parents with the lowest income and those with an income “slightly higher,” the former was associated with higher frequencies of homosexuality and bisexuality and high attraction scores toward the same sex for both male and female adult children. Moreover, a comparison between children from “slightly higher” income families and those that had “much higher” income also showed an increase in homosexuality, bisexuality, and same-sex attraction scores in the latter. We suggest that very high fetal estrogen and testosterone are both associated with nonheterosexual behavior in adult male and female children. That is, prenatal sex steroids are related to sexual orientation in a U-shaped fashion. The relationship between 2D:4D and sexual orientation should now be reexamined for curvilinear effects.
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