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Rachel Cook
Scientists who have carried out the world’s
largest study involving twins, both identical and fraternal, have found that
homosexuality is the result of random environmental factors and genetics.
The research, which looked at 3,826
same-gender twin pairs, was conducted by the Queen Mary’s School
of Biological and Chemical Sciences
and the Karolinska Institutet in Stockholm.
“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,” said Dr Qazi Rahman, the studies co-author,
in a media release.
Researchers looked at three areas of
possible influence on sexual orientation: genetics, shared environment (common
to identical and fraternal twins), and individual-specific environment factors,
which may include factors operating during foetal development.
The study found that genetics account for
35 percent of sexual orientation in men and 18 percent in women, while
individual-specific environmental factors accounted for 64 percent in both men
and women.
Shared environment factors explained 16
percent of the variation in same-sex behaviour in women.
“The study shows that genetic influences
are important but modest, and that non-shared environmental factors dominate,”
Rahman said.
The study is somewhat
supportive of the Australian Christian Lobby’s (ACL) view that homosexuality is
learnt behaviour. Victorian State Director of the ACL, Rob Ward, told MCV.
“The report confirms
the result of previous twin-based surveys that there is no ‘gay gene’. This has
been and remains our understanding."
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