SoSoGay – November 25th 2014

Research by a team from the University of Portsmouth has revealed that homosexuality in humans may have evolved as a result of the desire to bond with others.

Dr Diana Fleischman – an expert in the influences of hormones on the psychology of women – asked 244 men and women a series of questions designed to establish their feelings towards homosexuality. They then checked each person’s levels of progesterone, a hormone that has been shown to increase motivation to form close bonds, to see if there was a link between the levels of the hormone, and how they felt towards people of the same sex.

The initial online survey included questions such as, ‘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’. By checking the saliva of 92 of the women’s saliva, the researchers 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. The men that were 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.

She and her team found that heterosexual women who have higher levels of progesterone are more likely to be open to the idea of engaging in sexual behaviour with other women. Similarly, when heterosexual men are subtly reminded of the importance of having male friends and allies, they report more positive attitudes toward engaging in sexual behaviour with other men. This pattern is particularly dramatic in men who have high levels of progesterone.

Progesterone is produced mainly in the ovaries in women and in the adrenal glands in men. It is one of the main hormones responsible for caring or friendly behaviour and levels rise when people have close and friendly interactions. Women’s levels of progesterone peak after ovulation when the chance of becoming pregnant is dramatically reduced.

The study
, published in the journal Archives of Sexual Behavior may be the first evidence that our need to bond with others increases our openness to engaging in homosexual behaviour.

Dr Fleischman said: ‘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.’

‘From an evolutionary perspective we tend to think of sexual behaviour as a means to an end for reproduction. However, because sexual behaviour 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 behaviour even when reproduction is not possible.

‘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 behaviour occurs in those who don’t identify as homosexual.’

Read the article on the SoSoGay site here.