Preliminary results from a University of Portsmouth study provide evidence that the human need to bond with others is related to and increases openness to homosexual behavior. Their research is published in the journal, Archives of Sexual Behavior.
Dr Diana Fleischman’s study found that heterosexual women with higher levels of progesterone are more open to the idea of sexual behavior with other women. Heterosexual men with high levels of progesterone similarly are more inclined to exhibit more positive attitudes toward in sexual behavior with other men.
Several studies have shown that homosexuality is more common in brothers and others on the same maternal line. A genetic factor is theorized to be the cause.
But since LGBT people have fewer children than straight people, this theory presents a paradox from an evolutionary perspective: how would this trait persist over generations if the men carrying genetic component do not reproduce?
The hormone progesterone contributes to the inclination to form social bonds in humans. This inclination is beneficial for the survival of humans; the formation of friendly same-sex alliances between males promotes community-building. This research suggests that homosexual behavior may have evolved to promote social bonding in humans.
Progesterone is produced in the adrenal glands in men and in the ovaries in women. The hormone level rises during close and friendly interactions between people. Progesterone levels in women peak after ovulation when the chance of becoming pregnant is dramatically reduced. Other experimental research has shown that progesterone increased when both male and female subjects were told they would have an opportunity to affiliate with others following an experience of social rejection.
Dr Fleischman said: “From an evolutionary perspective we tend to think of sexual behavior as a means to an end for reproduction. However, because sexual behavior is intimate and pleasurable, it is also used in many species, including non-human primates, to help form and maintain social bonds. We can all see this in romantic couples who bond by engaging in sexual behavior even when reproduction is not possible.
“The results of our study are compelling because using two very different methods, they arrived at the same conclusion. Women were more likely to be motivated to think about homosexual sex when their levels of progesterone were higher. Compared to a control group, men’s homoerotic motivation was not increased by priming them with sex but thinking about friendship and bonding caused a measurable change in their attitude to the idea of having sex with other men.”
Having homoerotic thoughts does not necessarily mean they would be acted upon.
Dr Fleischman, an expert in the influences of hormones on the psychology of women, was studying the effect of progesterone on attitudes towards homosexuality. She questioned whether progesterone, a hormone that has been shown to increase motivation to form close bonds, might also underlie the motivation to affiliate with those of the same sex, sexually.
The researchers first developed a measure of homoerotic motivation through an online survey of 244 participants, with questions including: ‘The idea of kissing a person of the same sex is sexually arousing to me’ and ‘If someone of the same sex made a pass at me I would be disgusted’. The researchers then measured progesterone in 92 women’s saliva and found that as progesterone increased so too did openness to the idea of engaging in homosexual activity.
In the next study, the researchers measured levels of progesterone in the saliva of 59 men before all were randomly assigned to one of three groups and asked to complete word completion puzzles, one using friendship words, one using sexual words, and a third using neutral words. Men asked to complete the affiliative/friendship word puzzle showed 26 per cent greater homoerotic motivation compared to the men in the sexual or neutral conditions. In addition, those men with the highest progesterone in the affiliative condition showed 41 per cent greater homoerotic motivation compared to high progesterone men in the other two groups.Studies of other animals in the great ape family also point to homosexual behavior being used to maintain and forge new friendships.
Dr Fleischman said: “Humans are among a group of animals who have sex for many reasons, not just to reproduce. Reasons can include pleasure, a reward, a way of saying ‘please be nice to me’ or exerting dominance. It’s very complex, but it’s clear there’s a continuum between affection and sexuality and sexuality is fluidity, that is, the ability to engage sexually with those of the same sex or the opposite sex is common. In humans, much, if not most of same-sex sexual behavior occurs in those who don’t identify as homosexual.”
The researchers will now explore other contexts and hormonal influences that could increase homoerotic motivation in men and women. They are also interested in seeing how bisexual people might react differently to social cues.