Another policy under pressure is the “14-day rule,” a widely employed convention that natural embryos should not be grown longer than two weeks in the lab. Though it’s a mostly arbitrary stopping point, it’s been convenient for laboratory scientists to know where their limit is. But that rule isn’t being applied to the embryo models. For instance, even though the United Kingdom has a 14-day rule enshrined in law, that legislation doesn’t define what an embryo is. To scientists working on models, that’s a critical loophole. If the structures aren’t considered true embryos, then the rule doesn’t apply.
Last year, the University of Cambridge, in the UK, described the situation as a “grey area” and said it “has left scientists and research organisations uncertain about the acceptable boundaries of their work, both legally and ethically.”
Researchers at the university, which is a hot spot for human embryo models, have been working with one that has advanced features, including beating heart cells. But the appearance of distinctive features under their microscopes is unsettling—even to scientists. “I was scared, honestly,” Jitesh Neupane, who led that work, told the Guardian in 2023. “I had to look down and look back again.”
That particular stem-cell model isn’t complete—it entirely lacks placenta cells and a brain. So it’s not a real embryo. But it could get ever trickier to insist the models don’t count, given the accelerating race to make them more realistic. To Duboule, scientists are caught in a “fool’s paradox” and a “rather unstable situation.”
Even incomplete models raise the question of where to draw the line. Should you stop when it can feel pain? When it’s just too human-looking for comfort? Scientific leaders may soon have to decide if there are “morally significant” human features—like hands or a face—that should be avoided, whether the structure has a brain or not. “I personally think there should be regulation, and many in the field believe this too,” says Alejandro De Los Angeles, a stem-cell biologist affiliated with the University of Central Florida.
“I always live in fear that I might find myself embroiled in some kind of a scandal … Things can shift very quickly for political reasons.”
Jacob Hanna
Hanna says he has all the necessary approvals in Israel to carry his work forward. But he also worries that the ground rules could change. “I’m almost the only one [in Israel] doing these kinds of experiments, and I always live in fear that I might find myself embroiled in some kind of a scandal,” he says. “Things can shift very quickly for political reasons.”
And his statements about the situation in Gaza have made him a target. He’s gotten voicemails wondering why a Weizmann professor is so sympathetic to Palestine, and once when he returned from a trip, someone had tucked an Israeli army beret into the door handle of his car. Last year, he says, political opponents even went after his science by filing a complaint that his research was illegal.
What is clear is that Hanna, who is gregarious and attentive, has worked to cultivate a large group of friends and allies, including religious authorities—all part of a campaign to explain the science and hear out other views. He says he got a perfect grade in a bioethics class with a rabbi, conferenced with a priest from his hometown in Galilee, and even paid his respects to an Orthodox professor at a conservative hospital in Jerusalem. “It was unofficial. I didn’t have to get a permit from him,” Hanna says. “But … what does he think? Can I get him on board? Do I get a different opinion?”