On Sunday, The New York Times reported that the Trump administration plans to define “gender” based on people’s external genitalia, as part of their larger efforts to roll back protections for transgender Americans. They say they plan to implement a definition of gender “grounded in science.” As a physician who studies gender, I can tell you this is ludicrous. There is no scientific definition of gender.

The Trump administration seems to think you can separate people’s genitalia into two binary categories: male and female. This is not a scientific reality. Thousands of people in the United States have genitalia that do not fall into these categories. We previously referred to these people as having “disorders of sexual development.” More recently, as we recognized that there is no reason to pathologize these people, the term became “differences of sex development1." Examples include people who have a vagina along with testicles or people with both a uterus and male-appearing external genitalia. Somewhere between one in 1,500 and one in 4,500 infants are born with external genitalia. This means there are as many as 200,000 such people in the United States.

The Trump administration says they will use to determine a person’s gender when the anatomy is not clear. They are likely under the wrong impression that all people have XY or chromosomes or that people’s chromosomes invariably define their gender. What will they do with the people who have chromosomal mosaicism, a condition in which some of their cells have XY chromosomes and others have XX chromosomes? People with another condition called complete androgen insensitivity syndrome have XY chromosomes but lack receptors that respond to . They have breasts and vaginas and almost always identify as women. Does the administration plan on telling them that they are actually, in fact, men?

Medicine has a dark history of trying to force people into gender identities that don’t fit. The most famous case is that of David Reimer, a person whose penis was mutilated during a botched circumcision. Doctors tried to force a female gender on David by surgically creating a vagina and telling his parents to raise him as a girl. They were certain he would identify as female. David Reimer suffered from horrible , later identified as male, and killed himself with a sawed-off shotgun at age 38. Doctors now recognize that physical characteristics alone do not determine gender identity. Things like anatomy and chromosomes just don’t cut it. The only way to know someone’s gender is to ask them.

One also needs to ask why this policy is needed. As Dr. Yee-Ming Chen, director of the Disorders of Sexual Development Program at Boston Children’s Hospital asks, “What good could possibly come from this?” Given that the Trump administration has a history of promoting against transgender people—efforts to ban them from the military, making them use bathrooms that do not correspond with their gender identity—​​​​​​​it seems clear that this is just another attempt to attack the transgender community.

In addition to stigmatizing the thousands of people with differences of sexual development, this policy from the administration invalidates the experiences of over one million transgender people living in the United States. Large surveys have shown that these people are our neighbors, friends, and family, living in every state of our nation. Science has shown that when we reject their identities, they have worse mental health and higher risks of suicide. Studies from all over the world have shown that when we try to force people into gender binaries, their mental health is worse. We can’t let the Trump administration use fake “science” to drive our transgender and gender diverse neighbors to . We need to stand up for their rights and mental health.

Jack Turban MD MHS is a resident physician in at The Massachusetts General Hospital and McLean Hospital, where he researches gender and . His writing has appeared in The New York Times, Vox, Scientific American, and Psychology Today, among others. You can follow him on Twitter @jack_turban.

1 Many also find this term less than ideal and feel that it is stigmatizing.