The first time Ashley McGuire had a baby, she and her husband had to wait 20 weeks to learn its sex. By her third, they found out at 10 weeks with a blood test. Technology has defined her pregnancies, she told me, from the apps that track weekly development to the ultrasounds that show the growing child. “My generation has grown up under an entirely different world of science and technology than the Roe generation,” she said. “We’re in a culture that is science-obsessed.”

Activists like McGuire believe it makes perfect sense to be pro-science and pro-life. While she opposes abortion on moral grounds, she believes studies of fetal development, improved medical techniques, and other advances anchor the movement’s arguments in scientific fact. “The pro-life message has been, for the last 40-something years, that the fetus … is a life, and it is a human life worthy of all the rights the rest of us have,” she said. “That’s been more of an abstract concept until the last decade or so.” But, she added, “when you’re seeing a baby sucking its thumb at 18 weeks, smiling, clapping,” it becomes “harder to square the idea that that 20-week-old, that unborn baby or fetus, is discardable.”

Scientific progress is remaking the debate around abortion. When the U.S. Supreme Court decided Roe v. Wade, the case that led the way to legal abortion, it pegged most fetuses’ chance of viable life outside the womb at 28 weeks; after that point, it ruled, states could reasonably restrict women’s access to the procedure. Now, with new medical techniques, doctors are debating whether that threshold should be closer to 22 weeks. Like McGuire, today’s prospective moms and dads can learn more about their baby earlier into a pregnancy than their parents or grandparents. And like McGuire, when they see their fetus on an ultrasound, they may see humanizing qualities like smiles or claps, even if most scientists see random muscle movements.

These advances fundamentally shift the moral intuition around abortion. New technology makes it easier to apprehend the humanity of a growing child and imagine a fetus as a creature with moral status. Over the last several decades, pro-life leaders have increasingly recognized this and rallied the power of scientific evidence to promote their cause. They have built new institutions to produce, track, and distribute scientifically crafted information on abortion. They hungrily follow new research in embryology. They celebrate progress in neonatology as a means to save young lives. New science is “instilling a sense of awe that we never really had before at any point in human history,” McGuire said. “We didn’t know any of this.”

In many ways, this represents a dramatic reversal; pro-choice activists have long claimed science for their own side. The Guttmacher Institute, a research and advocacy organization that defends abortion and reproductive rights, has exercised a near-monopoly over the data of abortion, serving as a source for supporters and opponents alike. And the pro-choice movement’s rhetoric has matched its resources: Its proponents often describe themselves as the sole defenders of women’s welfare and scientific consensus. The idea that life begins at conception “goes against legal precedent, science, and public opinion,” said Ilyse Hogue, the president of the abortion-advocacy group NARAL Pro-Choice America, in a recent op-ed for CNBC. Members of the pro-life movement are “not really anti-abortion,” she wrote in another piece. “They are against [a] world where women can contribute equally and chart our own destiny in ways our grandmothers never thought possible.”

In their own way, both movements have made the same play: Pro-life and pro-choice activists have come to see scientific evidence as the ultimate tool in the battle over abortion rights. But in recent years, pro-life activists have been more successful in using that tool to shift the terms of the policy debate. Advocates have introduced research on the question of fetal pain and whether abortion harms women’s health to great effect in courtrooms and legislative chambers, even when they cite studies selectively and their findings are fiercely contested by other members of the academy.

Not everyone in the pro-life movement agrees with this strategic shift. Some believe new scientific findings might work against them. Others warn that overreliance on scientific evidence could erode the strong moral logic at the center of their cause. The biggest threat of all, however, is not the potential damage to a particular movement. When scientific research becomes subordinate to political ends, facts are weaponized. Neither side trusts the information produced by their ideological enemies; reality becomes relative.

Abortion has always stood apart from other topics of political debate in American culture. It has remained morally contested in a way that other social issues have not, at least in part because it asks Americans to answer unimaginably serious questions about the nature of human life. But perhaps this ambiguity, this scrambling of traditional left-right politics, was always unsustainable. Perhaps it was inevitable that abortion would go the way of the rest of American politics, with two sides that share nothing lobbing claims of fact across a no-man’s land of moral debate.

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When Colleen Malloy, a neonatologist and faculty member at Northwestern University, discusses abortion with her colleagues, she says, “it’s kind of like the emperor is not wearing any clothes.” Medical teams spend enormous effort, time, and money to deliver babies safely and nurse premature infants back to health. Yet physicians often support abortion, even late into fetal development.

As medical techniques have become increasingly sophisticated, Malloy said, she has felt this tension acutely: A handful of medical centers in major cities can now perform surgeries on genetically abnormal fetuses while they’re still in the womb. Many are the same age as the small number of fetuses aborted in the second or third trimesters of a mother’s pregnancy. “The more I advanced in my field of neonatology, the more it just became the logical choice to recognize the developing fetus for what it is: a fetus, instead of some sort of sub-human form,” Malloy said. “It just became so obvious that these were just developing humans.”

Malloy is one of many doctors and scientists who have gotten involved in the political debate over abortion. She has testified before legislative bodies about fetal pain—the claim that fetuses can experience physical suffering, perhaps even prior to the point of viability outside the womb—and written letters to the U.S. Senate Judiciary Committee.

Her career also shows the tight twine between the science and politics of abortion. In addition to her work at Northwestern, Malloy has produced work for the Charlotte Lozier Institute, a relatively new D.C. think tank that seeks to bring “the power of science, medicine, and research to bear in life-related policymaking, media, and debates.” The organization, which employs a number of doctors and scholars on its staff, shares an office with Susan B. Anthony List, a prominent pro-life advocacy organization.

“I don’t think it compromises my objectivity, or any of our associate scholars,” said David Prentice, the institute’s vice president and research director. Prentice spent years of his career as a professor at Indiana State University and at the Family Research Council, a conservative Christian group founded by James Dobson. “Any time there’s an association with an advocacy group, people are going to make assumptions,” he said. “What we have to do is make our best effort to show that we’re trying to put the objective science out here.”

This desire to harness “objective science” is at the heart of the pro-science bent in the pro-life movement: Science is a source of authority that’s often treated as unimpeachable fact. “The cultural authority of science has become so totalitarian, so imperial, that everybody has to have science on their side in order to win a debate,” said Mark Largent, a historian of science at Michigan State University.

Some pro-life advocates worry about the potential consequences of overemphasizing the authority of science in abortion debates. “The question of whether the embryo or fetus is a person … is not answerable by science,” said Daniel Sulmasy, a professor of biomedical ethics at Georgetown University and former Franciscan friar. “Both sides tend to use scientific information when it is useful towards making a point that is based on … firmly and sincerely held philosophical and religious convictions.”

For all the ways that the pro-life movement might be seen as countering today’s en vogue sexual politics, its obsession with science is squarely of the moment. “We’ve become steeped in a culture in which only the data matter, and that makes us, in some ways, philosophically illiterate,” said Sulmasy, who is also a doctor. “We really don’t have the tools anymore for thinking and arguing outside of something that can be scientifically verified.”

Sometimes, scientific discoveries have worked against the pro-life movement’s goals. Jérôme Lejeune, a French scientist and devout Catholic, helped discover the cause of Down syndrome. He was horrified that prenatal diagnosis of the disease often led women to terminate their pregnancies, however, and spent much of his career advocating against abortion. Lejeune eventually became the founding president of the Vatican’s Pontifical Academy for Life, established in 1994 to navigate the moral and theological questions raised by scientific advances against a “‘culture of death’ that threatens to take control.”

When scientific evidence seems to undermine pro-life positions on issues such as birth control and in vitro fertilization, pro-lifers’ enthusiasm for research sometimes wanes. For example: Some people believe emergency contraception, also known as the morning-after pill or Plan B, is an abortifacient, meaning it may end pregnancies. Because the pill can prevent a fertilized egg from implanting in a woman’s uterus, advocates argue, it could end a human life.

Sulmasy, who openly identifies as pro-life, has argued against this view of the drug—and found it difficult to reach his peers in the movement. “It’s been very difficult to convince folks within the pro-life community that the science seems to be … suggesting that [Plan B] is not abortifacient,” he said. “They are too readily dismissing that work as being motivated by advocacy.”

And at a basic level, the argument for abortion is also framed in scientific terms: The procedures are “gynecological services, and they’re health-care services,” Cecile Richards, the president of Planned Parenthood, says. This alone is enough to make even gung ho pro-life advocates wary. “Science for science’s sake is not necessarily good,” said McGuire, who serves as a senior fellow at the Catholic Association. “If anything, that’s what gave us abortion. … When the moral and human ethics are removed from it, it’s considered a medical procedure.”

Even with all these internal debates and complications, many in the pro-life movement feel optimistic that scientific advances are ultimately on their side. “Science is a practice of using systematic methods to study our world, including what human organisms are in their early states,” said Farr Curlin, a physician who holds joint appointments at Duke University’s schools of medicine and divinity. “I don’t see any way it’s not an ally to the pro-life cause.”

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Pro-lifers’ enthusiasm for science isn’t always reciprocated by scientists—sometimes, quite the opposite. Last summer, Vincent Reid, a professor of psychology at Lancaster University in the United Kingdom, published a paper showing that late-development fetuses prefer to look at face-like images while they’re in the womb, just like newborn infants. As Reid told The Atlantic’s Ed Yong, the study “tells us that the fetus isn’t a passive processor of environmental information. It’s an active responder.”

After his research was published, Reid suddenly found himself showered with praise from American pro-life advocates. “I had a few people contacting me, congratulating me on my great work, and then giving a kind of religious overtone to it,” he told me. “They’d finish off by saying, ‘Bless you,’ this sort of thing.” Pro-life advocates interpreted his findings as evidence that abortion is wrong, even though Reid was studying fetuses in their third trimester, which account for only a tiny fraction of abortions, he said. “It clearly resonated with them because they had a preconceived notion of what that science means.”

Reid found the experience perplexing. “I’m very proud of what I did … because it made genuine advances in our understanding of human development,” he said. “It’s frustrating that people take something which actually has no relevance to the position of anti-abortion or pro-abortion and try to use it … in a way that’s been pre-ordained.” He’s not going to stop doing his research on fetal development, he said. But he “will probably be a bit more heavy, perhaps, in my anticipation of how it’s going to be misused.”

This fate is nearly impossible to avoid in any field that remotely touches on abortion or origin-of-life issues. “There [are] no people who are just sitting in a lab, working on their projects,” said O. Carter Snead, a professor of law and political science at Notre Dame who served as general counsel to President George W. Bush’s Council of Bioethics. “Everybody is politicized.” This is true even of researchers like Reid, who was blindsided by the reaction to his findings. “You can’t do this and not get sucked into somebody’s orbit,” said Largent, the Michigan State professor. “Everyone’s going to take your work and use it for their ends. If you’re going to do this, you either decide who’s going to get to use your work, or it’s done to you.”

That can have a chilling effect on scientists who work in sensitive areas related to conception or death. Abortion is “the third-rail of research,” said Debra Mathews, an associate professor of pediatrics at Johns Hopkins who also has responsibility for science programs at the university’s bioethics institute.* “If you touch it, your research becomes associated with that debate.” Although the abortion debate is important, she said, it can be intimidating for researchers: “It tends to envelop whatever it touches.”

As often as not, scientists dive into the debate, taking funding from pro-life or pro-choice organizations or openly advancing an ideological position. This, too, has consequences: It casts doubt on the validity and integrity of any researcher in bioethics-related fields. “Anybody with money can get a scientist to say what they want them to say,” said Largent. “That’s not because scientists are whores. It’s because the world is a really complex place, and there are ways that you can craft a scientific investigation to lend credence to one side or another.”

This can have a fun-house-mirror effect on the scientific debate, with scholars on both sides constantly criticizing the methodological shortcomings of their opponents and coming to opposite conclusions. For example: Priscilla Coleman is a professor at Bowling Green State University who studies the mental-health effects of abortion. Coleman has testified before Congress, and pro-life advocates cite her as an important scholar working on this issue. At least some of her work, however, has been challenged repeatedly by others in her field: When she published a paper on the connection between abortion and anxiety, mood, and substance-abuse disorders in 2009, for instance, a number of scholars suggested her research design led her to draw false conclusions. She and her co-author claimed they had only made a weighting error and published a corrigendum, or corrected update. But ultimately, the author of the dataset Coleman used concluded that her “analysis does not support … assertions that abortions led to psychopathology.”

“If the results are questionable or not reproducible, then the study gets retracted. That’s what happens in science,” Coleman said in an interview. “The bottom line was that the pattern of the findings did not change.” She expressed frustration at media reports that questioned her work. “I’m so past trying to defend myself in these types of articles,” she said. “To me, there isn’t anything much worse than distorting science for an agenda, when the ultimate impact falls on these women who spend years and years suffering.”

At least in one respect, she is correct: Her opponents often do have affiliations with the pro-choice movement. In this case, one of the researchers questioning her work was associated with the Guttmacher Institute, a pro-abortion organization. In an email, Lawrence Finer, the co-author who serves as Guttmacher’s vice president for research, said that Coleman’s results were simply not reproducible. While Guttmacher advocates for abortion rights, the difference, Finer claimed, is that it places a priority on transparency and integrity—which, he implied, the other side does not. “It’s actually not difficult to distinguish neutral analysis from advocacy,” he wrote in an email. “The way that’s done is by making one’s analytical methods transparent and by submitting one’s analysis—‘neutral’ or not—to peer review. No researcher—no person, for that matter—is neutral; everyone has an opinion. What matters is whether the researcher’s methods are appropriate and reproducible.”

“There is a false equivalence between the science and what [Coleman] does,” added Julia Steinberg, an assistant professor at the University of Maryland’s School of Public Health and Finer’s co-author, in an email. “It’s not a debate, the way global warming is not a debate. There are people claiming global warming is not occurring, but scientists have compelling evidence that it is occurring. Similarly, there are people like Coleman, claiming abortion harms women's mental health, but the scientists have compelling evidence that this is not occurring.”

Yet, even the academy that establishes and promotes transparent methodologies for science research has its own institutional biases. Since support for legal abortion rights is commonly seen as a neutral position in the academy, said Sulmasy, openly pro-life scholars may have a harder time getting their colleagues to take their work seriously. “If an article is written by somebody who … is affiliated with a pro-life group or has a known pro-life stand on it, that scientific evaluation is typically dismissed as advocacy,” he said. “Prevailing prejudices within academia and media” determine “what gets considered to be advocacy and what is considered to be scientifically valid.”

Pro-life optimists believe those biases might be changing—or, at least, they hope they’ve captured the territory of scientific authority. As the former NARAL president Kate Michelman told Newsweek in 2010, “The technology has clearly helped to define how people think about a fetus as a full, breathing human being … The other side has been able to use the technology to its own end.” In recent years, this has been the biggest change in the abortion debate, said Jeanne Mancini, the president of March for Life: Pro-choice advocates have largely given on up on the argument that fetuses are “lifeless blobs of tissue.”

“There had been, a long time ago, this mantra from our friends on the other side of this issue that, while a little one is developing in its mother’s womb, it’s not a baby,” she said. “It’s really hard to make that argument when you see and hear a heartbeat and watch little hands moving around.”

Ultimately, this is the pro-life movement’s reason for framing its cause in scientific terms: The best argument for protecting life in the womb is found in the common sense of fetal heartbeats and swelling stomachs. “The pro-life movement has always been a movement aimed at cultivating the moral imagination so people can understand why we should care about human beings in the womb,” said Snead, the Notre Dame professor. “Science has been used, for a long time, as a bridge to that moral imagination.”

Now, the pro-life movement has successfully brought their scientific rallying cry to Capitol Hill. In a recent promotional video for the Charlotte Lozier Institute, Republican legislators spoke warmly about how data helps make the case for limiting abortion. “When we have very difficult topics that we need to talk about, the Charlotte Lozier Institute gives credibility to the testimony and to the information that we’re giving others,” said Tennessee Representative Diane Black. Representative Claudia Tenney of New York agreed: “We’re winning on facts, and we’re winning hearts and minds on science.”

This, above all, represents the shift in America’s abortion debate: An issue that has long been argued in normative claims about the nature of human life and women’s autonomy has shifted toward a wobbly empirical debate. As Tenney suggested, it is a move made with an eye toward winning—on policy, on public opinion, and, ultimately, in courtrooms. The side effect of this strategy, however, is ever deeper politicization and entrenchment. A deliberative democracy where even basic facts aren’t shared isn’t much of a democracy at all. It’s more of an exhausting tug-of-war, where the side with the most money and the best credentials is declared the winner.

* This article has been updated to clarify that Mathews helps run science programs at the Johns Hopkins Berman Institute of Bioethics, rather than the institute itself.