More than 1,600 scientists released an open letter Thursday opposing the Trump administration’s memo erasing legal protections for trans people.

The letter, signed by over 700 biologists, 100 geneticists, and nine Nobel laureates, pushed back on the administration’s claim that defining sex according to observed genitals at birth or a genetic test is grounded in science. “This proposal is fundamentally inconsistent not only with science, but also with ethical practices, human rights, and basic dignity,” read the letter. “The proposal is in no way ‘grounded in science’ as the administration claims. The relationship between sex chromosomes, genitalia, and gender identity is complex, and not fully understood.”

For the scientists behind the letter, it was important to step forward and oppose a policy that they felt was misinterpreting the scientific understanding of sex and gender. “It appears the Trump administration is trying to eliminate the entire concept of gender as a thing separate from sex, in the sense that they believe that they can stop allowing transgender people to self-identify as transgender by requiring everybody to be defined as a binary sex from birth,” said Rachael French, a biology professor at San Jose State University.

“They’ve suggested at least two things: what your genitalia look like when you’re born or whether you have a Y chromosome,” she said in an interview with Rewire.News. “You can’t even test for what sex a person is, let alone be able to define what gender a person is based on their chromosomes. The entire idea from a biological standpoint is ridiculous.”

French said trans people won’t be the only ones negatively affected by the sex definition proposed by the administration. She worried that intersex people could be forced into painful and unnecessary surgeries as children in order to make their genitals conform to the legal definitions of sex being pushed by the Trump administration. Even cisgender people with natural genetic variations could be legally forced into another sex thanks to an invasive government genetics test.

The open letter wasn’t the only response to the anti-trans memo from the scientific community since it was first reported by the New York Times. Science journal Nature pushed back on the administration’s scientific justification for discrimination in an editorial, saying the memo “has no basis in science” and calling for the move to be “abandoned.” A piece in Scientific American called the proposed policy “scientifically absurd.” And Trump’s Centers for Disease Control director, Robert Redfield, said the stigma against the trans community stemming from the policy is “not in the interest of public health.”

For trans women like Tessa Fisher, a third year PhD student at Arizona State University studying astrobiology, coverage of Trump’s anti-trans memo made her feel “scared but also furious.”

The response from her scientific peers has been heartening. “It’s been really amazing,” she told Rewire.News. “Partially because these people are my peers for the most part, and it’s a really nice thing, [it’s] sort of affirming that a lot of the people out there that I work with and I read their papers and I’m sort of doing the same things they are respect who I am. Which is really, really encouraging. It’s a great show [of] genuine allyship.”

With everyone in her life perceiving her as female, Fisher pointed to the sheer impracticality of the plan to erase trans people from existence. “From like a day-to-day point of view [it] makes absolutely no goddamn sense whatsoever. It would literally be pointless for me to call myself male, even if I wanted to, because no one would see me as that.”

Fisher is particularly frustrated about the way those who oppose trans rights have tried to co-opt science for their own means. “There’s the presumption that they know more about the scientific research than I do, even though I’m the one working on a PhD in that,” she said. “In a lot of cases, it’s at the same time kind of shocking how shallow their understanding of science is. The best example I’ve ever had of that is that some Twitter troll who had been picking a fight with me earlier actually tweeted at my advisor and the profile for my program to complain that they had not taught me taxonomy correctly. Which was creepy and also kind of pathetic.”

The public seems to hold overly simplistic ideas about the science of sex and gender, according to scientists. “There is zero scientific evidence for anybody to feel that people, children or anybody else, should have to choose one particular gender,” Mollie Manier, a biology professor at George Washington University, told Rewire.News. Manier’s research focuses on the evolutionary genetics of reproduction.

“If you look across multiple cultures, and apparently even within the history of the U.S., there’s a lot of gender fluidity .… When people are allowed to be more gender-fluid culturally, they often are, and that’s reflecting more of a biological reality that gender is not a binary always,” she said.

Manier, who helped draft the letter, reiterated that there is no genetic test that could conclusively determine a person’s sex or gender. “Even if there were, it is totally inappropriate to use that in order to override an individual’s lived experience of what they think in their heart of hearts they are.”