In November, Feng Zhang attended the Hong Kong conference where researcher He Jiankui shocked the world by announcing that he'd engineered humanity's first gene-edited babies.
When Zhang, a pioneer of the revolutionary gene-editing technology CRISPR that He had used, got back home to the Broad Institute in Cambridge, he debriefed with its founding director, Eric Lander.
"We began talking about [how] this is really a very important moral dilemma that we're facing as a society, and it's important not to be gray about it," Zhang says. "This is something where we should take a black-and-white stance."
That stance is now out in the journal Nature: a call by leading scientists for a global moratorium on creating gene-edited babies. The piece is signed by 18 prominent scientists and ethicists, and endorsed by science leaders, including the director of the National Institutes of Health.
"The statement is quite simple," Zhang says. "We should not use germline editing" — that is, changing DNA in sperm, eggs or embryos, that can be passed down to future generations — "to create genetically modified babies at this point."
The article also argues that the world needs a long-term international forum to address the wisdom of altering humanity's gene pool, some sort of global framework that includes scientists, ethicists and members of the public.
Countries may decide individually, the scientists suggest, but consult with that body if they decide they want to lift the moratorium and move forward with some sort of human gene editing.
"We thought a lot about it, and said, 'This is a decision that's got to be made at the level of nations,' " Lander says.
And this approach may be how we have to think about managing many powerful technologies in the future, he adds, in situations where there's no way to enforce limits on countries against their will, but an approach of "anything goes" doesn't make sense either.
"Do we want a world where countries are doing really adventurous modification of the human genome to — oh, I don't know, make astronauts who can resist radiation and go into space, or have other kinds of biological properties?" he asks. "I worry that we haven't thought through any of that right now. "
At this point, such gene-editing is not safe anyway, he says, "but the bigger issue is, is it wise? And when might it be wise? So it's really setting up some kind of appropriate international governance framework to talk about this going forward."
There are efforts already under way by the World Health Organization and multiple national academies of science to create committees that will try to oversee what happens to the human genetic legacy.
But they don't preclude this call for a new global body, says George Annas, director of the Center for Health Law, Ethics & Human Rights at Boston University School of Public Health.
"We're going to need many organizations pulling together on this one, because there really is no precedent for this," says Annas, co-author of "Genomic Messages: How the Evolving Science of Genetics Affects Our Health, Families, and Future."
He welcomes the proposal in Nature, though he questions the idea of letting individual countries decide an issue that affects the human gene pool at the level of the whole species.
"If they think that editing the human genome of embryos to try to make 'a better baby,' or a different baby, or a genetically modified baby is wrong, it's wrong for everybody," he says. "It's not just wrong for my country or your country."
Is it wrong? The leading scientists and ethicists who wrote the piece in Nature say that's a question all of humanity needs to consider in the coming years.
NPR reporter Rob Stein writes about the more immediate debate around the Nature proposal here:
In the United States, federal law prohibits the creation of gene-edited babies. And about 30 countries have similar prohibitions. But many others do not.
The call for a global moratorium is being welcomed by many scientists and bioethicists.
"The philosophical and theological consequences of re-writing our own instruction book are sufficiently major that somebody like me — who generally is opposed to the idea of moratoriums — feels that it's time to stop and look very carefully at the pros and cons," Dr. Francis Collins, who directs the National Institutes of Health, tells Shots. Collins co-wrote an article supporting the call.
But some scientists and bioethicists, while agreeing it's far too soon for anyone to try to make gene-edited babies, worry about using the word moratorium.
"I'm concerned a moratorium complicates future discussions rather than clarifying them," says Dr. George Daley, dean of the Harvard Medical School.
"How long should a moratorium last? Who gets to decide how and when to rescind a moratorium? Is such a call going to prompt even more restrictive attempts to legislate the science and prohibit any clinical work?" Daley says.
Some fear a moratorium could drive scientists underground.
"I don't think we want to drive people into hiding over this," says Jennifer Doudna, a University of California, Berkeley, biochemist who helped develop CRISPR. "Instead, I would like to have a much more open, transparent international conversation. I don't like the word moratorium because it kind of goes against that spirit."
But others welcome the call, saying clearer statements by groups like the National Academy of Sciences might have prevented He Jiankui from doing what he did.
"Although it would have been a lot better if the call for an explicit moratorium had been proactive rather than reactive, better late than never," Ben Hurlbut, a bioethicist at Arizona State University writes in an email.
Some say a moratorium is crucial to prevent scientists from trying to create "designer babies."
"This statement is saying, 'Hey. Wait. Stop. This is too important to have small groups of scientists who've taken it upon themselves to be making these decisions for all of humanity,' " says Marcy Darnovsky, who runs the Center for Genetics & Society, a watchdog group.
"Allowing reproductive gene-editing would open the door to certain people whose parents were able to afford genetic upgrades being considered superior to everyone else," Darnovsky says. "The last thing we want to do is build a future in which we're creating classes of people who are considered genetic-haves and others who are have-nots."
"The world must unite to prevent there being a fleet of offshore boats with a little designer-baby logo on them," says Fyodor Urnov, a visiting scholar at the Innovative Genomics Institute at the University of California, Berkeley. "It's not too late to prevent that from happening. And we must."
The presidents of the U.S. National Academy of Medicine and National Academy of Sciences, and the Royal Society in Britain, wrote another accompanying article noting that they are working to develop an international consensus on standards that should apply to such research.
"We must achieve broad societal consensus before making any decisions, given the global implications of heritable genome editing," they write.
Is there a rush? After all, genetic change is slow in a species whose generations run about 30 years.
"I don't know," Lander says. "If it became suddenly very trendy to make a certain genetic change for your children, I could imagine a lot of pressure on parents."
It's true that genetic change moves slowly, he says, "but that's why it's important we get this right," because mistakes are hard to reverse. And "we want the public engaged, because scientists can't make these decisions by themselves."
For now, Lander's colleague Zhang says the message to parents who might contemplate some sort of genetic enhancement for their children is quite simple: Forget it.
"Because we cannot do it in a way that would be good for the children, or the children's children," he says. "Don't even think about it."
This segment aired on March 14, 2019.