Could genetics have something to do with gender identity? For decades it was an almost taboo question, but science has been gathering clues for years. A recent study published in Scientific Reports (a journal of the Nature group) has for the first time brought together twins and non-identical twins from several specialized clinics in an attempt to rigorously separate what genetic inheritance contributes from what hormones in the maternal womb contribute.
Twins, the perfect tool of genetics
Identical twins (monozygotic) share practically 100% of their DNA. Non-identical twins (dizygotic), only about 50%, the same as any pair of siblings. Comparing how much both types of pairs “resemble” each other in a specific trait is one of the classic methods of genetics for calculating how much inheritance weighs.
The Australian team collected data from 27 pairs of twins from two clinics specialized in gender identity and combined them with previous studies that used similar methods. In total, they added up 463 pairs of twins and non-identical twins.
A striking result
The numbers speak clearly. Among identical twins, 21.2% of the pairs were concordant: that is, if one of the two had a diverse gender identity, the other did too. Among non-identical twins, that percentage fell to 8.7%. Since identical twins share more DNA, the fact that they match twice as often points directly to a hereditary component.
The authors estimated that, starting from a prevalence of around 1% in the general population, the relative risk of an identical twin sharing the condition was 21.2, compared with 8.7 in non-identical twins. It is a large and statistically significant difference.
And the pregnancy hormones?
There was another hypothesis at play: that exposure to sex hormones during pregnancy (for example, from one twin to the other within the womb) influenced the development of gender identity. If that theory were true, opposite-sex non-identical twins should match more than same-sex ones. It was not the case: concordance was practically the same (9.2% versus 8.2%), which does not support a prominent role for prenatal hormones.
What does this mean in practice?
That a diverse gender identity is not a “choice” nor something inherited in a simple way from a single gene. As happens with most complex human traits, it seems to be the result of a sum of small genetic factors that combine with the environment.
This type of research is important because it helps to understand the biological basis of a condition that affects many people, and to banish myths: it is neither something “contagious” nor does it respond to a single cause. Science, little by little, is drawing a more precise map of human nature.
Source: Using twin data to examine heritable and intrauterine hormonal influences on transgender and other gender-diverse identities. Conabere W, Ravine D, Malta S, et al. Scientific Reports 15 (2025). DOI: 10.1038/s41598-025-06265-6.
