Genetics, along with hormones² and upbringing, may play a part in sexuality, according to a study.

一项研究显示，除了荷尔蒙和教育方式外，基因也会对性取向产生影响。

Researchers claim it is known that there are well-established traits which differ between girls and boys, with, for example, boys more likely to engage in 'rough and tumble' play.

Children who later become gay or lesbian are more likely to differ from these expected traits, or gender³ conformity⁴（一致，适合） , said a team from Queen Mary University in London.

Between 50 to 80 percent of gender non-conforming boys become gay, and around a third of non-conforming girls become lesbian.

Now, doctors Andrea Burri and Qazi Rahman believe that in girls, genes⁵ may be partially⁶ responsible for gender non-conformity and, by association, sexual orientation⁷.

They followed a group of 4000 female twins, asking them about their sexual attractions and gender non-conformity.

They discovered genetic¹ influences on sexual orientation (25 percent) and childhood gender nonconformity (31 percent), reports journal PLoS One.

Dr Rahman said: ‘We found that there is a connection between these mental traits and how sexual orientation develops.

‘One idea is that there is an association between these psychological traits and sexual orientation because they all develop under common biological drivers; like the development of brain regions under the influence of genes and sex hormones.

‘We think environmental factors and genetics drive other mechanisms⁸, like exposure to sex hormones in the womb（子宫） , to shape differences in gender nonconformity and sexuality simultaneously⁹.’

Dr Rahman said the results showed non-conforming behaviour came 'from within', and proved that mental health issues such as depression which have been associated with such behaviour was due to negative reactions from others.