Scientists have discovered how to keep human embryos alive in the laboratory much longer than ever before. They hope the discovery will yield new insights into human development and help prevent miscarriages and birth defects. NPR health correspondent Rob Stein reports that the step has revived debate about how long scientists should be allowed to experiment on human embryos.
ROB STEIN, BYLINE: Scientists have been able to make and study human embryos in their labs for decades, but Ali Brivanlou at the Rockefeller University says they could never keep them alive outside a woman's womb for very long.
ALI BRIVANLOU: What was possible before was to look at the human embryo for the first week but nothing after that. That was completely a black box.
STEIN: Which means scientists had no way to really study early human development and know next to nothing about how a tiny ball of cells starts to become a complex human.
BRIVANLOU: I find this to be a bit embarrassing because I know more about the fruit fly and the frog than I know about my own development.
STEIN: But then scientists in Britain figured out how to keep mouse embryos alive a lot longer. Magdelena Zernicka-Goetz of the University of Cambridge led that team.
MAGDELENA ZERNICKA-GOETZ: We used specific mix of amino acids, or hormones and growth factors that would allow embryos to feel as good as they would feel in the body of the mother.
STEIN: The big question was, could the same brew keep human embryos alive longer, too? So both teams of scientists decided to give it a try, and it worked. Human embryos kept developing in the lab not just for another day or two or three but at least another week.
ZERNICKA-GOETZ: This was the very first time we were able to look at our own development through this very specific time window. And this is extremely important because the seventh day of development is the time when the human embryo becomes embedded within the body of the mother.
STEIN: Scientists had thought embryos could only keep developing if they were safely in the womb, getting instructions from the mother about what to do next. The scientists watched in awe as the embryos implanted in the dish like they would in the womb.
BRIVANLOU: That was a big eureka moment in the lab.
STEIN: And then the embryos started forming the very early stages of different complex organs and tissues and structures.
BRIVANLOU: That was a very big surprise to us and to the field.
STEIN: The advance should help scientists figure out all sorts of things. Why do so many pregnancies end in miscarriages? What causes birth defects?
BRIVANLOU: We will learn things we cannot even imagine.
STEIN: How do embryonic stem cells really work? Are there better ways to treat infertility?
BRIVANLOU: It's as if you say, if I look at new sets of Hubble Telescope pictures that I haven't seen yet, what will I learn from them? It's difficult to say until you look at them, but I can assure you that based on one week, we started seeing things in the human embryo that nobody else had seen not only in humans but in no other embryo of any mammals.
STEIN: But both groups of scientists stopped there. They didn't let the embryos develop past 14 days because of a rule that scientists have followed for decades, a rule that bans experiments on human embryos that are more than two-weeks old. Insoo Hyun is a bioethicist Case Western Reserve University.
INSOO HYUN: Policymakers and others have looked at that developmental time point and thought that might be actually significant for people's moral beliefs if they think that's when you get a unique individual for the first time.
STEIN: But Hyun thinks it might be time to rethink that rule.
HYUN: If there's no other way to retrieve valuable information that could be good for humankind, I think it's definitely worth discussing the possibility of renegotiating where that stopping point ought to be.
STEIN: But those who think experimenting on human embryos is morally wrong find going even further deeply troubling. Daniel Sulmasy is a doctor and a bioethicist at the University of Chicago.
DANIEL SULMASY: The 14-day rule has kept it pretty limited in terms of what scientists could do. Once that goes, then it begins to sort of say it's open season on human embryos; anything goes. And the question has to be, are there any limits to what we will do to human beings in order to gain scientific knowledge? And then who counts as a human being?
STEIN: For his part, Hyun stresses that any change to the 14-day rule should only happen if society can come up with a new rule that satisfies those kinds of moral qualms. This debate comes as experiments involving stem cells derived from human embryos have started to raise similar difficult questions. Rob Stein, NPR News.