Global warming isn’t the only vexing issue the world wrestled with this week.

While delegates gathered in Paris to discuss climate change, the International Summit on Human Gene Editing convened in Washington, D.C., to debate another conundrum: How far should scientists go when editing human DNA?

The main focus was whether scientists should be allowed to use powerful new genetic engineering techniques to edit genes in human eggs, sperm or embryos — an extremely controversial step that raises a host of thorny safety and ethical issues.

At the end of the meeting Thursday, conference organizers concluded it would be “irresponsible to proceed” with any attempt to create a pregnancy or a baby from human eggs, sperm or embryos that have been altered, because of safety and ethical concerns.

But “intensive basic” research is “clearly needed and should proceed” to explore the safety and potential benefits of editing that kind of DNA, the committee said in a statement.

“That statement is our answer to the question of whether there should be a ban” on any further research, said David Baltimore, a Nobel Prize-winning biologist who chaired the committee.

Notably, the organizers didn’t rule out the possibility that gene editing someday could be used to create humans, as “scientific knowledge advances and societal views evolve.”

The organizers called for the creation of a ongoing forum to continue to assess the state of the research and society’s readiness.

Nearly 500 scientists, doctors, bioethicists, legal experts, historians, patient advocates and others convened for the summit, which was sponsored by the U.S. National Academy of Sciences, U.S. National Academy of Medicine, Chinese Academy of Sciences and the U.K.’s Royal Society.

An international committee organized by the U.S. academies attended the summit as part of its fact-finding process for issuing recommendations for possible guidelines for gene editing. Those are expected next year.

The meeting was convened because of rising concerns sparked by the development of gene-editing techniques such as CRISPR-Cas9. These techniques allow scientists to make very precise changes in DNA much more easily than ever before.

Scientists believe the new techniques will produce many benefits, such as finding new ways to prevent and treat diseases, including AIDS, cancer and Alzheimer’s.

But the ability to edit DNA so easily is also raising many fears, especially about the prospect of changing human DNA from the the very start. Scientists explored how altering sperm, eggs and embryos could yield important new insights into basic human biology and development, and help prevent and treat many inherited diseases, including Huntington’s disease, cystic fibrosis and Tay-Sachs disease.

But altering the so-called germline in this manner has long been considered off-limits. That’s because such changes can be passed down to future generations. Mistakes could inadvertently introduce new diseases into the human gene pool.

Another fear is that taking this step would open the door to designer babies — creating children who are smarter, taller, smarter or have other supposedly desirable traits.

During his opening remarks, Baltimore referred to Aldous Huxley’s 1932 book Brave New World. “The warning implicit in his book is one that we should take to heart today as we face the prospect of new and powerful means to control the nature of the human population,” Baltimore said.

Another speaker, Daniel Kevles, a Yale University medical historian, reminded the audience that eugenics was once widely accepted in the United States. “Eugenics was not unique to the Nazis; it happened everywhere,” Kevles said.

Many scientists stressed that they are nowhere near having the ability to genetically engineer complex traits. But one prominent geneticist speculated that attempts to enhance the human race could start with medical research.

“I think enhancement will creep in the door in terms of treating serious diseases,” said George Church of Harvard University. The ability to improve memory might start with research aimed at treating Alzheimer’s disease, for example, Church said.

There seemed to be general agreement that the safety concerns make it far too early to try to make a baby using eggs, embryos or sperm with edited DNA. But there is a split about what should be allowed short of that.

Some, such as Catholic bioethicist Hille Haker of Loyola University in Chicago, called for a moratorium on any experiments, at least until scientists have more time to understand how to use the new gene-editing techniques and society has more time to debate the complex issues they raise.

Others feared a moratorium would stymie a promising field at an important moment. They argued that basic studies in the lab should proceed.

“We all have an inescapable moral duty: to continue with scientific investigation to the point at which we can make a rational choice,” said John Harris, a professor of bioethics at the University of Manchester in England. “It seems to me, consideration of a moratorium is the wrong course. Research is necessary.”

But Jennifer Doudna of the University of California, Berkeley, a pioneer in the development of CRISPR-Cas9, repeated her position that research involving the technique should proceed cautiously.

One of the most emotional moments occurred when Sarah Gray of the American Association of Tissue Banks addressed a panel of scientists from the audience. Choking back tears, Gray described how her son suffered before dying of a genetic disorder six days after he was born. “If you have the skills and the knowledge to fix these diseases,” Gray said, “then freaking do it.”

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Transcript :

ROBERT SIEGEL, HOST:

How far should scientists be allowed to go when they edit human DNA? That’s the provocative question that was debated over the last three days at an unusual international conference in Washington, D.C. The conference came to a close this afternoon, and NPR health correspondent Rob Stein joins us now to talk about what happened. Rob, there’s been a lot of talk about how this could be a historic meeting. Why is that?

ROB STEIN, BYLINE: Yeah, Robert. The meeting is called the International Summit on Human Gene Editing. And you know, I’ve been to a lot of scientific meetings over the years, and I was really struck at this meeting at how the sense of history really permeated the meeting. There’s a real sense that scientists could be on cusp of taking an historic step that could have profound implications, profound benefits for society but also come with some equally profound dangers.

SIEGEL: Let’s step back a little. What prompted this meeting?

STEIN: Yeah. You know, Robert, scientists have known how to do genetic engineering – you know, make changes in DNA – for decades. What’s new is they recently developed some powerful new techniques that allow them to make really precise changes in DNA much more easily than ever before. So that’s letting them make change that they could only dream of before.

SIEGEL: What kinds of things are they talking about trying to do?

STEIN: Well, there’s a long list of things that they’ve already started to try to do using these new techniques. Most of them involve trying to find new ways to prevent and treat lots of diseases – everything from AIDS to cancer to Alzheimer’s disease. But there’s also some things they’re doing that are making people very nervous.

And the one that’s creating the biggest fuss, that was really the focus of this meeting, this summit, is that they’ve started to make changes in the DNA in human sperm, eggs and embryos. And that’s something that always has been considered off-limits because this is the sort of DNA that’s passed down for generations, you know, when people talk about passing on their genes to their children.

And so if you make changes in this DNA, it could become a permanent part of the human genetic blueprint and really, in some ways, could be seen as changing the course of human evolution. So you can see how the stakes suddenly get much higher.

SIEGEL: But describe why they would want to do that. And also, what’s the danger in doing that?

STEIN: Absolutely. So during the summit, they talked about a lot of positive things that could come out of this. They could get some really important insights into human biology and human development, and they could also find ways to eradicate some terrible genetic diseases – you know, diseases that are passed down through families, like Tay-Sachs or Huntington’s or Cystic Fibrosis. That’s on the positive side.

On the negative side, one of the big concerns is they could simply make a mistake. This is very new science. They don’t really know how to use it yet. And if they could make a mistake that results in new diseases, then that’d kind of mess up the human gene pool for generations.

SIEGEL: And other items on the negative side here?

STEIN: Yeah, there are. And one of the big ones is that, you know, if scientists do this for medical reasons, what’s to stop them for doing it for other reasons, like, for example, to try to create what people call designer babies. You know, these are children that are smarter, taller, better athletes or something like that. Scientists are nowhere near being able to actually do that right now, but someday they might be able to. And if they let them do it for medical reasons, what’s to stop them from doing it for other reasons? And that starts to conjure up all kinds of scary “Brave New World” images of, you know, genetically engineering a super race or something like that.

SIEGEL: So scientists from all over the world who engaged in these matters came to Washington, talked for three days. What’s the outcome of it all?

STEIN: Yeah, so at the end of it after hearing about the science and the ethics and the legal issues that are raised both in the United States and internationally, the organizing committee issued a surprisingly specific statement. They said, very clearly, there’s no way we’re try to create a pregnancy or baby this way. It’s just too dangerous and too unsafe. But they did strongly endorse doing the basic research in the laboratory to find out what’s possible, what’s safe and check in periodically as this proceeds to see if society has reached a consensus on whether we should take the next step or not.

SIEGEL: OK. That’s NPR health correspondent Rob Stein. Rob, thanks.

STEIN: Thank you. Transcript provided by NPR, Copyright NPR.