Genetics plays a role in male sexual orientation but social
and environmental factors are also involved, research suggests.

Scientists tested the DNA of 410 pairs of homosexual twins,
making this the largest study of its kind. They found that homosexual men
shared genetic markers in a region of chromosome 8, and the Xq28 region of the
X chromosome.

The findings were originally presented by Professor
Michael Bailey at the annual meeting of the American Society of Human Genetics two years ago. They
appear to have been resurrected for an event at the periphery of another major
conference this year.

'When people say there's a gay gene, it's an
oversimplification', said Dr Alan Sanders, who co-led the study. 'It seems like
there's a number of genes involved so there's more work to do to narrow things
down'.

The results confirm those of a similar study conducted by Dr Dean Hamer, which caused controversy at the time of its
publication in 1993. Media attention centred on the prospect of a prenatal test
for sexual orientation, with the Daily Mail running the headline: 'Abortion
hope after "gay genes" finding'. Last year, Dr Hamer responded
that any such test would be 'wrong, unethical and a terrible abuse of
research'.

Professor Bailey conceded the possibility that his research
could 'one day lead to a pre-natal test for male sexual orientation', though
noted that such a test would not be very accurate. 'Clearly parents should not
be allowed to torture or kill babies. But they can currently choose to
terminate a pregnancy early on, so they should be allowed to have as much
information on the future child as possible'.

Dr Qazi Rahman, a psychologist at King's College London, who was not involved with
the study, said that the results were important for our understanding of male
sexual orientation.

'This is not controversial or surprising and is nothing
people should worry about', he said, speaking to The Guardian. 'All human psychological traits are heritable, that is, they have a
genetic component. So we need to do "gene finding" studies like this
[...] to have a better idea where potential genes for sexual orientation may
lie'.

He added that, in his opinion, genetics explained '30 to 40
percent of the variation between people's sexual orientation'.

The
findings have not been published in a peer-reviewed journal.