This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Public debate surrounding transgender and gender-diverse (trans) people often centers 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 questioned. Instead, it's treated as a biological reality. However, when it comes to trans people, an alternative 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 that the likelihood of being trans is influenced by genes.
Twin studies are a powerful tool in research. Identical twins share 100% of their genes, whereas nonidentical twins share 50% on average—the same as nontwin 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 nonidentical twins, simply because of their greater genetic similarity. Conversely, if genes aren't involved, we expect to see similar rates of shared traits among identical and nonidentical pairs. Our research examined data from 463 twin pairs in which at least one was trans—the most comprehensive analysis on this topic to date.
After determining whether twin pairs were identical or nonidentical, we measured how often both twins were trans and compared this with instances in which only one was trans. Our results showed that among identical twins, if one was trans, the likelihood that the other was also trans was 21.2%. For nonidentical twins, this rate was significantly lower, at 8.7%—though this was still well above the 1–2% prevalence of trans identities in the general population.
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