

Dr Diana Fleischman, of the University of Portsmouth, says that the results of a preliminary study provide the first evidence that our need to bond with others increases our openness to engaging in homosexual behaviour.

She examined the relationship between the hormone progesterone and sexual attitudes to explore the role that homosexual behaviour may have played in cementing alliances over the course of human evolution.

In research published in the journal Archives of Sexual Behaviour, they 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.


Dr Fleischman said that this pattern was particularly obvious in men who have high levels of progesterone.




Women's levels of progesterone peak after ovulation when the chance of becoming pregnant is dramatically reduced.

Dr Fleischman said: "From an evolutionary perspective we tend to think of sexual behaviour as a means to an end for reproduction.



"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.


Men asked to complete the affiliative/friendship word puzzle showed 26% 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% greater homoerotic motivation compared to high progesterone men in the other two groups.


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.


