A scientist who denied the existence of bisexual men has admitted it is biologically possible to be attracted to both sexes.
Fifteen years after a controversial report, Dr Gerulf Rieger from the University of Essex presents ‘robust evidence’ that bisexuality is not just a label but a biological fact.
In a U-turn on his previous findings, Dr Rieger presents ‘compelling evidence’ that bisexual-identified men show bisexual genital and subjective arousal patterns.
Researchers based their findings on an analysis of more than 400 men’s penile responses to erotic videos of men and women.
Male sexual orientation is expressed on a continuum rather than ‘dichotomously’ – divided into two parts or classifications, Dr Rieger and his co-authors say.
Male sexual orientation and arousal encompasses a ‘range’, with heterosexuality on one end, homosexuality on the other and bisexuality in the middle.
Pictured: Dr Gerulf Rieger. His scepticism stemmed from a previous small study he had done with Professor J. Michael Bailey of Northwestern University in 2005, and which found no evidence of bisexual arousal in men
Male bisexuality had been challenged based on the assumption that men are either straight or gay, with ‘nothing in between’, but this study indicates that bisexual men have been ‘telling the truth’, according to the university.
Dr Gerulf Rieger said: ‘It has always been clear that bisexual men exist in terms of self-identity and behaviour, but many, including myself, were sceptical about their ability to be sexually aroused to both men and women.
‘Now, with this exceptional number of participants, we have clear proof of their bisexual arousal.
‘This reshapes our entire understanding of male sexual orientation.’
Dr Riegers and Professor J. Michael Bailey or Northwestern University in the US had published a small study back in 2005 disputing the existence of bisexuality.
They wrote: ‘Male bisexuality appears primarily to represent a style of interpreting or reporting sexual arousal rather than a distinct pattern of genital sexual arousal.’
The study was based on experiments at the university at the time, which were covered by the New York Times in an article titled ‘Straight, Gay or Lying?’, causing dismay in the bisexual community.
The researchers had found that three quarters of men who described themselves as bisexual had the same sort of arousal patterns as gay men when showed erotic films.
The remaining quarter had arousal patterns from heterosexual men, which led to report that bisexuality did not physically exist.
However, a further study by the same team in 2011 confirmed the existence of bisexual arousal in men.
The new analysis includes data from both of these studies, as well as six others, which affords ‘much greater statistical power’ than data from any of the individual studies on their own.
‘We investigated whether men who self-report bisexual feelings tend to produce bisexual arousal patterns,’ the researchers say.
‘Prior studies of this issue have been small, used potentially invalid statistical tests, and produced inconsistent findings.’
The existence of male bisexuality is contested by some, with sceptics claiming that men who self-identify as bisexual are actually either homosexual or heterosexual
Researchers combined nearly all available data, from eight previous American, British and Canadian studies, to form a dataset of more than 500 men around 29 years of age, much larger than any previous individual study, and conducted rigorous statistical tests.
Each study assessed changes in the penile circumference of participants, most of which were collected using a strain gauge around the penis.
The eight previous studies used Kinsey scores – a measure of self-reported sexual orientation used by many researchers – and measures of genital and self-reported arousal to erotic stimuli.
The Kinsey scale describes a person’s sexual orientation, ranging from 0 (heterosexual) to 6 (homosexual).
In the bisexual Kinsey score range (2-4), the men showed smaller differences in genital arousal to male versus female erotic stimuli, compared with exclusively heterosexual and homosexual men having Kinsey scores of 0 and 6, respectively.
Self-reported arousal across the Kinsey scale – a measure of self-reported sexual orientation used by many researchers. The scale describes a person’s sexual orientation, ranging from 0 (heterosexual) to 6 (homosexual)
Genital arousal patterns (above) aligned with self-reported sexuality in the Kinsey scale (as seen in the first image). In the bisexual Kinsey score range (2-4), the men showed smaller differences in genital arousal to male versus female erotic stimuli
Researchers also considered two measures – firstly, whether erotic videos of women aroused bisexual men more than they aroused gay men and whether erotic videos of men aroused bisexual men more than they aroused straight men.
Bisexual men were aroused more in both instances, they found.
Secondly, they examined the difference in each man’s arousal to women and men, to see if bisexual men would show less difference in arousal to women and men, compared with straight and gay men.
Bisexual men showed less difference to arousal in both sexes, they also concluded.
The results showed smaller differences in bisexual men’s genital arousal to male versus female erotic stimuli, compared with exclusively heterosexual and homosexual men.
‘Our results paint a powerful picture of male sexual orientation having gradients and nuance,’ said lead author Jeremy Jabbour, a PhD candidate at Northwestern University.
‘Although I don’t think that bisexual men need research like this to validate or justify their lived experience to others, I’m hopeful that findings such as ours will continue to help the public see the many shades of gray that exist in human sexuality.’
One of the co-authors of the paper is John Sylla, president of the American Institute of Bisexuality, a charity focused on bisexual research and education.
Sylla said people who are purely straight or purely gay can ‘generalise their own experience’ and think all other people ‘must be one or the other’.
‘There are bisexually aroused men and women, even if for different reasons they choose to pass as just straight or gay,’ he said.
The studies only concern bisexual men because ‘the existence of female bisexuality has been less controversial’.
The study, ‘Robust evidence for bisexual orientation among men’, has been published in Proceedings of the National Academy of Sciences.
WHAT DO SCIENTISTS THINK LEADS TO SAME-SEX ATTRACTION?
Scientists have long sought to quantify the extent to which genetic and non-genetic (or environmental) factors impact a person’s preference for same-sex relationships.
Previous studies had hinted that genetic factors were complex, but their relatively small scales made it hard to draw reliable conclusions.
In the new study, researchers used data from over 470,000 people, over a 100 times more than previous works.
They confirmed that homosexuality stems from both environmental and genetic factors.
Rather than their being one single ‘gay gene’, however, the team found thousands of places – or loci – in the genome that seem to play a role in sexuality.
Only five of these had a ‘significant’ impact — and, combined, all the factors accounted for only 8–25% of the variation in sexual attraction between different people.
The factors at play are so complex that is impossible to predict from a person’s DNA whether they are attracted to members of the same-sex or not.