To hear the bill’s sponsors tell it, the Pain-Capable Unborn Child Protection Act (H.R. 36) is about safeguarding fetuses that science has proven are capable of feeling pain. “No pain capable baby should have to undergo agonizing dismemberment in an elective late term abortion,” wrote the bill’s sponsor, Republican Arizona Congressman Trent Franks, in a Fox News commentary. If the bill is passed by the Senate — though that looks unlikely — the law would make it illegal for any person to perform or attempt to perform an abortion if the probable post-fertilization age of the fetus is 20 weeks or more. But despite the scientific trappings, the heart of this debate, like many political debates, is about ideology and values, not science.

But let’s discuss the research for a moment. The bill uses a lot of scientific-sounding arguments to make its case, but abortion-rights advocates argue that the conclusions it reaches run counter to current scientific research about fetal development. Jennifer Gunter, an OB-GYN and pain medicine physician, said the first thing to know is that the bill’s framing of this as a 20-week ban is misleading: It’s a 22-week ban. That’s because the 20-week post-fertilization point referred to in the bill is what physicians refer to as 22 weeks of gestational age, which is counted from the first day of the pregnant woman’s last menstrual period.

But even at 22 weeks, a human fetus doesn’t have the capacity to experience pain, according to evidence cited by abortion-rights supporters. “Rigorous scientific studies have found that the connections necessary to transmit signals from peripheral sensory nerves to the brain, as well as the brain structures necessary to process those signals, do not develop until at least 24 weeks of gestation,” according to a 2013 statement on fetal pain titled “Facts Are Important,” released by the American Congress of Obstetricians and Gynecologists (ACOG). “Because it lacks these connections and structures, the fetus does not even have the physiological capacity to perceive pain until at least 24 weeks of gestation,” continues the statement, which cites a review of the evidence published in the Journal of the American Medical Association and a report from the Royal College of Obstetricians and Gynecologists. This month, the ACOG issued a new statement opposing H.R. 36, saying the bill “limits access to safe, evidence-based care.”

National Right to Life, an anti-abortion group whose model legislation was used to write H.R. 36, contends that the scientific evidence that ACOG cites is incomplete. According to Jennifer Popik, director of federal legislation for National Right to Life, the fundamental split in thinking here is over whether a fetus needs to have a fully formed and connected cerebral cortex before it can feel pain. The ACOG statement and the researchers who published the JAMA review say that brain structure is a prerequisite for experiencing pain, but National Right to Life says it isn’t. “There’s an entirely other body of research that says you don’t actually need the cortex to experience pain, that the cortex helps you modulate it,” Popik said. “We’re always looking for ways to talk about the baby — to keep the baby in the debate. This is a good way to do it, because it’s legally sound and scientifically sound,” Popik said.

Among the evidence presented in the bill to support its contention that a fetus can feel pain at 20 weeks post-fertilization is the fact that anesthesia is often used during fetal surgery. The JAMA review, however, concluded that such anesthesia is given to inhibit fetal movement and for the mother’s benefit, not for fetal pain. The bill also states that 20 weeks after fertilization, a fetus can react “to stimuli that would be recognized as painful if applied to an adult human, for example, by recoiling,” but Gunter said that this is not evidence that the fetus is feeling pain. “It’s only pain when the brain assembles a signal and tells you it’s pain,” she said. “Neither withdrawal reflexes nor hormonal stress responses to invasive procedures prove the existence of fetal pain,” according to the JAMA review, because these same responses can be elicited by nonpainful stimuli and may occur without conscious processing in the brain.

But this particular debate over what the science does and doesn’t show is largely a distraction, because what we have here isn’t a scientific debate, but a moral one. Each side is using science to support age-old value judgments about when life begins and how the rights of a pregnant person are weighed against the rights that a fetus may or may not have; new scientific evidence is unlikely to change many minds.

National Right to Life believes human life begins when an egg is fertilized, and several of the bill’s other proponents have also been clear that they’d like to ban abortion altogether. For example, a 2010 brief about fetal pain published by the Family Research Council, another anti-abortion group and supporter of the bill, states that, “The humanness of the unborn child is not contingent on its capacity for pain. Whether or not an unborn child can feel pain is irrelevant to the respect that an unborn person deserves.”

Opponents of the bill say the intent of the fetal pain language is to change the focus of the debate. “Obviously, no one wants fetuses to experience pain, and that evokes a lot of emotion in people,” said Kristyn Brandi, an OB-GYN with the ACOG. “But this legislation is not based on facts.”