Arguments about nature versus nurture have long been part of debates about gender and sexuality. Like gay, lesbian and bisexual people before them, transgender people often encounter claims that their gender identity results primarily from environmental influences, social trends, or peer pressure.

A new study of twins has challenged that assumption. The researchers said their findings challenge the notion that being transgender is a choice or something that can be learned and therefore unlearned.

The research suggests that transgender identity may be influenced in part by genetics.

Researchers Dr Ken Pang, Dr Anja Ravine, and Will Conabere from Murdoch Children’s Research Institute, alongside Kellan Baker from Johns Hopkins University, examined twins to explore how frequently transgender identities occur within twin pairs.

They studied 463 sets of twins in which at least one twin was transgender, making it the largest study of its kind to date. Identical twins share 100% of their genes, while non-identical twins share approximately 50% on average, similar to non-twin siblings. Twin studies can help researchers determine whether genetics may play a role in human development.

The results showed that among identical twins, if one twin was transgender, there was a 21.2% likelihood that the other twin was also transgender. Among non-identical twins, the rate was significantly lower at 8.7%, although still considerably higher than the estimated 1% to 2% prevalence of transgender identities in the general population.

These findings suggest that genetic factors may contribute to a person’s gender identity, while environmental and developmental influences are also likely to play a role.

Read the full report at The Conversation.