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

Public debate surrounding transgender and gender diverse individuals often hinges on a single question: what defines a trans person? Most would agree that gender identity is an intrinsic part of one's being, not a choice. However, when it comes to trans individuals, another explanation emerges: that trans identities and gender diversity are the result of environmental factors, such as social trends or peer pressure.

This framing suggests that a trans identity is a choice that can be unlearned. Such messaging is used to deny the existence of trans people, restrict access to necessary healthcare, and fuel discrimination. Our study of twins challenges this notion, showing that genetics play a significant role in trans identity. Twin studies are a powerful tool in research, allowing us to compare the influence of genes and environment on human traits.

Identical twins share 100% of their genes, while non-identical twins share 50%, on average. By comparing these two types of twins, we can determine the extent to which genetics and environment contribute to being trans. If genes are involved, we'd expect identical twins to share the trait more often than non-identical twins. Our research examined data from 463 twin pairs, with at least one being trans – the most comprehensive analysis on this topic to date.

We found that among identical twins, if one was trans, the likelihood that the other was also trans was 21.2%, compared to 8.7% for non-identical twins. This difference, while still above the 1–2% prevalence of trans identities in the general population, suggests that genes are involved in shaping trans identity. However, it's important to note that most twin pairs, even identical ones, are not both trans.

This pattern is consistent with other human traits, which are shaped by both genetic and environmental factors. Genes and the environment do not act independently; rather, hundreds or thousands of genes work alongside and react to environmental influences. Environmental factors can affect gene activity throughout life, influenced by experiences from conception.

Both identical and non-identical twins share environmental experiences, but each twin also has unique experiences that contribute to individual differences. Our findings provide crucial evidence that genes and biological pathways play a role in shaping gender identity. This dispels the myth that gender diversity is entirely socially determined and serves as a counterargument to harmful public attitudes and policies that seek to restrict trans people's rights.