How to define identity

Researchers say gender identity comes from the brain, not the body. Some put it more bluntly: It originates between your ears, not between your legs. But the forces that acted on the brain to shape that identity are not understood, and physical or chemical differences in the brain that might relate to gender have not been well defined.

No one knows for sure why body and mind sometimes do not match. But being transgender is not a matter of choice, Dr. Safer said. It is not a fad or a whim. For transgender people, it is generally an overwhelming sense that their gender is not the one on their birth certificate. And gender is not about whom they’re attracted to — it’s about who they are.

Distress over the mind-body mismatch can become especially intense around puberty, and the risk of suicide shoots up for young people in this situation. Mainstream medicine has begun to recognize how serious an issue it is: Last month, the American Academy of Pediatrics issued its first-ever policy statement regarding care for transgender children and adolescents, and those who are “gender-diverse,” or non-binary, meaning they are neither clearly male or female.

The pediatric statement urged a “gender-affirming approach,” which translates as respecting and supporting children, even young ones, in “their self-expressed identity.” The society also noted that transgender young people “have high rates of depression, anxiety, eating disorders, substance use, self-harm and suicide.”

Last year, the Endocrine Society — the professional group for experts in the glands and organs that produce hormones — issued guidelines for treating transgender people. They said gender identity was biologically based, and urged federal and private insurers to cover medical needs related to it for transgender people.

It’s not as simple as X and Y

Apart from transgender issues, other conditions make it clear that defining male and female is not so simple. For instance, there are people with XY chromosomes — which makes them genetically male — who look, act and feel like women because their bodies cannot react to male hormones.

In other cases, some women with a condition that exposed them to high levels of testosterone before birth identify as male — but many more with the same condition do not.