Do genes contribute to homosexuality?
In the 19th century, some researchers believed that some people were ‘born’ homosexual and that other people ‘acquired’ homosexuality [16, 17]. These researchers speculated that genes could be involved in some homosexuality, while other people moved toward homosexuality because of psychological and social reasons. These early genetic theories were not based on hard scientific evidence since researchers at that time lacked the tools for direct genetic analysis that are available today. Mostly, the evidence for genes playing a role in sexual orientation was indirect. In the 1950s, one U.S. researcher offered some reason for thinking homosexuality might have a genetic basis: he showed that identical twins (monozygotic twins, who share the same DNA as each other) shared a homosexual orientation at a high rate [18]. Even so, this evidence was not definitive. Some commentators noted that the twins grew up in the same environments, which means that their sexual orientation might have another
