Lesbianism is at least 25% genetic, according to a study of twins conducted in Britain

The study found that identical twin sisters - who share 100% of their DNA - are more likely to both be lesbians than are fraternal twin sisters - who share just 50%. A female's sexual orientation also appears to be partly influenced by her level of exposure to the male sex hormone androgen when she is in the womb. Greater hormone exposure correlates with more gender nonconformity early in her life (as a child, she may be called a "tomboy"), as well as a same-sex orientation later on. A study by Dutch psychologists reported that 10% to 12% of male and female children who feel discomfort with their gender go on to identify as gay or lesbian as adults. Meanwhile, just 1% or 2% of children who are comfortable with their gender identity turn out to be gay or lesbian.