Scientists have found evidence to support the existence of a male genome which may influence homosexuality.
Dr Michael Bailey, from Northwestern University, studied 400 sets of twins to determine if some men are genetically inclined to be gay.
The study identified two areas on the male genome which appear to be linked to sexuality.
Bailey said: "Sexual orientation has nothing to do with choice. Our findings suggest there may be genes at play and we found evidence for two sets that affect whether a man is gay or straight."
Researchers took blood from 409 homosexual brothers and heterosexual members of their family. It is known that siblings share around 50 per cent of their DNA, but it is possible they have a chance of sharing genes associated with sexual orientation.
While the findings revealed genetics accounted for around 30% to 40% of a man's sexuality, the rest was based on social and environmental factors.
The study was presented at the American Association for the Advance of Science's annual conference in Chicago.
The research builds on work by Dean Hamer, the American geneticist who identified an area on the X chromosome that appeared to influence male sexuality in the 1990s.
Using DNA from gay man and their pedigrees, a gene for homosexuality seemed to be maternally linked and found on the Xq28 stretch of the X chromosome.
The latest study confirms this region is likely to be shared by gay twin brothers than by brothers and their other siblings.
Conservatives will hop on that 60-70% due to social and environmental factors though. Sort of proves that people are just predisposed to homosexuality.
