Both women repeatedly stressed that their out-of-work activities do not speak for their employers.

Separated by an ocean, Zelikova and Ramirez kept their friendship with each other alive through a running iMessage thread. Through the summer of 2016, they talked about their lives, shared interesting articles about the election, and traded photos of Ramirez’s puppy. And so it continued, right up to November 8.

All four women had been pulling for Hillary Clinton. They wore pantsuits to work that Tuesday, and they swapped triumphant flexed-arm and American flag emojis. Around 8 p.m., as the returns started to come in, their triumph turned into streams of expletive and anxious worrying.

They remember the next days as very bleak. There was a lot of cursing and fretting, and many fewer puppy photos than usual. But they resolved to fight back too. Two days after the election, with the blessing of the group, Ramirez sent out a message to 20 scientists whom she respected. Its subject: “battle plan.”

“We’re all very upset, and I don’t want us to forget the feeling we have right now,” the email said. “We’re scared and angry and we want to do something—so let’s do something.”

She tossed out a few ideas about what that “something” could be—publishing supportive op-eds, running for local office, promoting science-education programs—and she asked the group to add other women who might be interested in a similar approach. By the end of the day, her 20-person email had swelled to 100. By the weekend, 500 women were swapping ideas or asking for a next step.

That mailing list became 500 Women Scientists. What emerged wasn’t just a vague resolve to do something, but a decision to advocate for a specific set of ideas that they felt no one was saying in public. Over a week, the two women and some trusted mentors developed and wrote the group’s pledge, which they described as “an open letter from women scientists.”

The main thrust of the letter: If the government advances policies that threaten or terrify people who do science, it damages the scientific enterprise as a whole.

“Science is not supposed to be political. But if we’re humans, and we feel under threat, and our family and friends feel under threat, then we can’t do science,” Zelikova said. This works the other way, too. “When you threaten a particular discipline in science or science in general, you also threaten the people who are doing the science,” she told me.

Hence the open letter. It highlights that everyone in a democratic society depends on science, both to fuel continued technological advancement and to ground evidence-based policymaking. Then it says, in part:

The anti-knowledge and anti-science sentiments expressed repeatedly during the U.S. presidential election threaten the very foundations of our society. Our work as scientists and our values as human beings are under attack. We fear that the scientific progress and momentum in tackling our biggest challenges, including staving off the worst impacts of climate change, will be severely hindered under this next U.S. administration. … Many of us feel personally threatened by this divisive and destructive rhetoric and have turned to each other for understanding, strength, and a path forward. We are members of racial, ethnic, and religious minority groups. We are immigrants. We are people with disabilities. We are LGBTQIA. We are scientists. We are women.

The letter went live on Thursday, November 17, along with the names of the 500 signatories. Immediately it began to spread. By the end of day on Friday, it had 2,000 signatures. On Saturday, it had 5,000. On Monday, it hit 8,000. By the end of the month, more than 10,000 people had signed the letter.