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- Scientists looked at the link between progesterone and sexual attitudes
- Progesterone is a hormone that contributes to formation of social bonds
- Heterosexuals with more of the hormone are more open to homosexuality
- In men, thinking about social bonds and friendships had the same effect
- UK study claims there is a continuum between affection and sexuality
Homosexual behaviour may have evolved to improve how well humans bond and get along with each other, according to new research.
Researchers found that heterosexual women with high levels of the hormone progesterone are more 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.
The study provides the first evidence that our need to bond with others increases our openness to engage in homosexual behaviour.
The hormone progesterone is known to contribute to the formation of social bonds, which have many benefits for humans.
The hormone 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.
Dr Diana Fleischman from the University of Portsmouth said that the pattern was particularly obvious in men who had high levels of progesterone.
Women’s levels of progesterone peak after ovulation when the chance of becoming pregnant is dramatically reduced.
‘From an evolutionary perspective we tend to think of sexual behaviour as a means to an end for reproduction,’ said Dr Fleischman.
‘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.
‘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.’
Dr Fleischman said that, 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.
She said that having homoerotic thoughts did not necessarily mean they would be acted upon.
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 a second study, the researchers measured levels of progesterone in the saliva of 59 men before all were randomly assigned to one of three groups.
They were then asked to complete word puzzles, one using friendship words, one using sexual words, and a third using neutral words.
WHAT IS PROGESTERONE?
The hormone progesterone is known to contribute to the formation of social bonds, which have many adaptive benefits for humans.
The hormone 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.
This research looks at how 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.