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Is Homosexuality Genetic?

written by: Victoria Trix•edited by: Paul Arnold•updated: 11/21/2009

There is no clear cut answer to the origin of homosexual behaviour. Currently the consensus is leaning towards a largely genetic basis with a few environmental variables thrown in. It appears there is no single gay gene and no single environmental variable.

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    Is there a Gay Gene?

    While homosexuality is still a touchy subject in some circles, it is more widely accepted than it was ten years ago. Researchers are still intrigued, however, with the ‘why’ behind a person’s individual attraction to someone of the same sex. The question of whether or not homosexuality is genetic has yet to be answered as most researchers have not found any true biological basis to base their own studies on. Researchers and scientists do believe, though, that homosexuality actually stems from a combination of biological and environmental factors.

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    Causes of Homosexuality

    Sexual orientation is an incredibly complex area, but some researchers have tried to find a single genetic or environmental cause for homosexuality. This now does not seem to be the case according to the latest findings (June 2008) from the world's largest study of twins.

    The work was carried out by Dr Niklas Langstrom and colleagues at the Karolinska Institute in Sweden and the studies were of all adult (20-47 years old) twins in Sweden. Many genetic studies use identical and non-identical twins to tease out genetic and environmental influences. Identical twins share the same genes and environment and non-identical twins share half their genes and all their environment. If there is a greater similarity in trait between identical twins compared to non-identical twins, genetic factors are deemed largely to be responsible. So if scientists observe that same-sex behaviour is more common amongst identical twins, then there must be genetic factors at work.

    In this research the scientists asked all participants (same-gender twin pairs) about their sexual orientation and amount of same sex and opposite sex partners they had slept with

    They found that genetics accounted for about 35 per cent of the differences between men in homosexual behaviour and non-shared environmental factors about 64 percent.

    In homosexual women, 18 per cent of the variation in same-sex behaviour was accounted for by genetics, non-shared environment 64 percent and shared environment about 16 per cent.

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    Nature or nurture

    Although specific genes were not identified researchers believe they operate somewhere during development; an analysis of DNA should be able to provide some answers. Clearly from this latest research both nature and nurture play a role in homosexual behaviour.