Homosexual behavior due to genetics and environmental factors

Homosexual behaviour is largely shaped by genetics and random environmental factors, according to findings from the world's largest study of twins.

Writing in the scientific journal Archives of Sexual Behavior, researchers from Queen Mary's School of Biological and Chemical Sciences, and Karolinska Institutet in Stockholm report that genetics and environmental factors (which are specific to an individual, and may include biological processes such as different hormone exposure in the womb), are important determinants of homosexual behaviour.

Dr Qazi Rahman, study co-author and a leading scientist on human sexual orientation, explains: "This study puts cold water on any concerns that we are looking for a single 'gay gene' or a single environmental variable which could be used to 'select out' homosexuality - the factors which influence sexual orientation are complex. And we are not simply talking about homosexuality here - heterosexual behaviour is also influenced by a mixture of genetic and environmental factors.

The team led by Dr Niklas Långström at Karolinska Institutet conducted the first truly population-based survey of all adult (20-47 years old) twins in Sweden. Studies of identical twins and non-identical, or fraternal, twins are often used to untangle the genetic and environmental factors responsible for a trait. While identical twins share all of their genes and their entire environment, fraternal twins share only half of their genes and their entire environment. Therefore, greater similarity in a trait between identical twins compared to fraternal twins shows that genetic factors are partly responsible for the trait.

This study looked at 3,826 same-gender twin pairs (7,652 individuals), who were asked about the total numbers of opposite sex and same sex partners they had ever had. The findings showed that 35 per cent of the differences between men in same-sex behaviour (that is, that some men have no same sex partners, and some have one or more) is accounted for by genetics. Rahman explains:

"Overall, genetics accounted for around 35 per cent of the differences between men in homosexual behaviour and other individual-specific environmental factors (that is, not societal attitudes, family or parenting which are shared by twins) accounted for around 64 per cent. In other words, men become gay or straight because of different developmental pathways, not just one pathway."

For women, genetics explained roughly 18 per cent of the variation in same-sex behaviour, non-shared environment roughly 64 per cent and shared factors, or the family environment, explained 16 per cent.

The study shows that genetic influences are important but modest, and that non-shared environmental factors, which may include factors operating during foetal development, dominate. Importantly, heredity had roughly the same influence as shared environmental factors in women, whereas the latter had no impact on sexual behaviour in men.

Dr Rahman adds: "The study is not without its limitations - we used a behavioural measure of sexual orientation which might be ok to use for men (men's psychological orientation, sexual behaviour, and sexual responses are highly related) but less so for women (who show a clearer separation between these elements of sexuality). Despite this, our study provides the most unbiased estimates presented so far of genetic and non-genetic contributions to sexual orientation."

Source: Queen Mary, University of London

   

• fleem - Jun 29, 2008
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  "Homosexual behaviour is largely shaped by genetics and random environmental factors, according to findings from the world's largest study of twins."
  
  And to think before this study came out, we all thought it was based on the number of planets orbiting Proxima Centauri.
  
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• Modernmystic - Jun 29, 2008
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  Well this is ground breaking, hell EVERY facet of human behavior can be broken down to genetic or environmental factors. What would have been news is if they found it was exclusively one or the other that determines sexuality.
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• Captain_Sakonna - Jun 29, 2008
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  The title of the article is somewhat misleading in my opinion. The study indicates that there are certain genetic and environmental factors which INFLUENCE a person's sexual behavior, without necessarily CAUSING it. In other words, certain factors may predispose certain people to homosexual desires, without necessarily "forcing" them to carry those desires out. What I mean to say is that this study does not rule out the role of a person's own will in choosing how they will behave.
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• KB6 - Jun 29, 2008
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  I keep waiting for us to get over our obsession with seeing our sexuality in terms of gay, straight or bi. Human sexuality is so nuanced, so diverse that trying to tease out environmental and genetic factors to explain every point along the sexual continuum can never have more than the grossest predictive value.
  Either way, it's no big deal to me whether homosexuality is due to environmental factors, genes or is a "lifestyle choice." To paraphrase Jefferson's quote regarding how many god's one worships: It does me no injury for my neighbor to like men, women, or both. It neither picks my pocket nor breaks my leg.
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• Crossrip - Jun 30, 2008
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  I just think its ironic that this study came from a university who's first name is "Queen"
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• HenisDov - Jun 30, 2008
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  Homosexual behavior due to genetics and environmental factors?
  Highfalutin Gibberish
  
  A. http://www.eureka...2608.php
  
  "...our study provides the most unbiased estimates presented so far of genetic and non-genetic contributions to sexual orientation."
  
  
  B. Culture inheres in genetics
  
  Every cultural element is an artifact which involves biological intra-/inter-cell expression and/or process; biological and cultural domains are not ontologically distinct, but instead culture inheres in biology.
  
  Obviously and plainly every and all behaviours of every and all organisms are due to genetics and environmental factors...
  
  So what's this highfalutin gibberish?!
  
  
  Dov Henis
  
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