By Karen Weintraub
For nearly 40 years scientists have observed their self-imposed ban on doing research on human embryos in the lab beyond the first two weeks after fertilization. Their initial reasoning was somewhat arbitrary: 14 days is when a band of cells known as a primitive streak, which will ultimately give rise to adult tissues, forms in an embryo. It is also roughly the last time a human embryo can divide and create more than one person, and a few days before the nervous system begins to develop. But the so-called 14-day rule has held up all this time partly because scientists could not get an embryo to grow that long outside its mother’s body.
Researchers in the U.K. and U.S. recently succeeded for the first time in growing embryos in the lab for nearly two weeks before terminating them, showing that the so-called 14-day rule is no longer a scientific limitation—although it remains a cultural one. Now, a group of Harvard University scientists has published a paper arguing that it is time to reconsider the 14-day rule because of advances in synthetic biology.
The U.S. has no law against growing embryos beyond two weeks—as long as the research is not funded with federal dollars. But most scientific journals will not publish studies that violate the 14-day rule, and the International Society for Stem Cell Research requires its members to agree to the rule in order to qualify for membership.
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