New research provides initial evidence of a link between parents’ income and the sexual orientation of their adult offspring. The new findings have been published in the journal Evolutionary Psychology.
Although it is now widely accepted among scientists that attraction to same-sex partners is common in humans, the biological causes behind such attraction remain unknown. Researchers have been studying different factors such as genetics and hormones in an attempt to better understand the biology of sexual orientation.
“There appears to be a biological influence on same-sex attraction through exposure to testosterone prenatally (low testosterone in gay men and high in lesbians). Prenatal testosterone levels are probably influenced by genes and homosexuality tends to reduce offspring number,” said study author John T. Manning, a professor and honorary research fellow at Swansea University, and author of “The Finger Book: Sex, Behaviour and Disease Revealed in the Fingers.”
“We have recently shown that a marker for prenatal testosterone (the 2D:4D) varies in children across the income groups of their parents. Children from parents with low income show evidence of low prenatal testosterone and those from high income parents have high fetal testosterone.”
The 2D:4D ratio is believed to reflect the effects of prenatal hormone exposure. By examining the ratio of the length of the index finger (the second digit of a human hand) relative to the ring finger (the fourth digit), one can estimate how much testosterone and estrogen an individual was exposed to in utero.
“The differences in offspring 2D:4D across parental income groups prompted us to look at parental income as a correlate of the sexual orientation of their adult children. To our knowledge links between parental income and same-sex attraction in their children have not been previously explored.”
For their new study, the researchers analyzed data from a large-scale multiethnic and multinational survey. In July 2015, the British Broadcasting Corporation (BBC) coordinated an extensive internet study. Hundreds of questions were posed to participants from a variety of backgrounds from around the world in order to gain insight into demographics, personality traits, sexual behavior, and physical attributes. More than 255,000 individuals completed all study tasks.
As part of the survey, the participants measured the length of their index finger and ring finger of both their right and left hands. They also completed assessments of sexual orientation, sexual attractions, and parental income.
“A simple prediction would be that male children from low income parents and female children from high income parents would have elevated rates of same-sex attraction,” Manning said. However, a more complicated pattern of results were observed.
The researchers found a curvilinear relationship between parental income and self-identified sexual orientation of their adult children.
The highest frequencies of homosexuality and bisexuality for both women and men occurred among those who described their parent’s income as “much lower than others.” The lowest frequency of homosexuality occurred among those who described their parent’s income as “slightly higher than others,” while intermediate frequencies of homosexuality occurred among women and men who described their parent’s income as “much higher than others.”
The findings were similar when sexual attractions were considered.
The results provide evidence that “parental income may influence the probability of homosexuality/bisexuality in adult children,” Manning told PsyPost. “This finding is novel. However, we emphasize that we are talking about rather small differences in rates of same-sex attraction across parental income groups.”
“We looked at associations between parental income and same-sex attraction in children because we had earlier found that a marker for prenatal testosterone (2D:4D) was linked to parental income. Therefore, our findings are relevant to the prenatal origins of sexual orientation.”
“It appears that very low prenatal testosterone and very high prenatal testosterone may both be linked to same-sex attraction,” Manning explained. “The former may be associated with submissive sexual roles in gay men and femme identity in lesbians and the latter may be linked to assertive roles in gay men and a butch identity in lesbians.”
However, the new research includes some limitations. The predominant ethnicity was White (reported by 84.1% of participants) and the most commonly represented nationalities were the United Kingdom (46.9%) and the United States (27.7%).
“The links between parental income and the sexual orientation of their adult children have not been described before. Our sample is large, multiethnic and multinational. However, our analysis should be replicated in other large data sets.”
The study, “Parental Income and the Sexual Behavior of Their Adult Children: A Trivers–Willard Perspective“, was authored by John T. Manning, Bernhard Fink, and Robert Trivers.