Critics claim trans people ‘defy biology’. New research suggests otherwise

staticnak1983/Getty Images Public debate surrounding transgender and gender diverse (trans) people often centres on one fundamental question: what makes someone trans? Most of us would agree that our gender is not a choice, but a core part of who we are.

When our gender aligns with the sex listed on our birth certificate, it’s rarely ever questioned.

Instead, it’s treated as a biological reality .

However, when it comes to trans people, an alternate explanation is frequently floated: that trans identities and gender diversity are the result of environmental influences, such as social trends or peer pressure.

This framing treats a trans identity as a choice that can – and, implicitly, should – be unlearned.

Such messaging is increasingly being used to deny the existence of trans people, restrict access to medically necessary health care , and fuel discrimination .

Our study of twins challenges this idea and shows the likelihood of being trans is influenced by your genes.

The power of twin studies Twin studies are a powerful tool in research .

Identical twins share 100% of their genes, whereas non-identical twins share 50% on average – the same as non-twin siblings.

By comparing these two types of twins, we can explore the extent to which genetics and the environment contribute to human traits.

If genes are involved, we expect identical twins to share traits (for example, both identifying as trans) more often than non-identical twins, simply due to their higher degree of genetic similarity.

Conversely, if genes aren’t involved, we expect to see similar rates of shared traits among identical and non-identical pairs.

Our research examined data from 463 twin pairs where at least one was trans – the most comprehensive analysis on this topic to date.

After determining whether twin pairs were identical or non-identical, we measured how often both twins were trans, compared to instances where only one was trans.