Rumors have been buzzing for months that a team of Chinese researchers was intending to edit the genes of a human embryo. According to a study published this week in Protein & Cell, the rumors are true. And though the researchers took pains, there's no doubt that they've opened an ethical can of worms that will pit scientists against one another for years to come.

Proponents of embryonic genomic editing point out that it could help eradicate genetic diseases, including fatal ones such as Tay-Sachs disease. But those opposed have compelling arguments, too: the person into whom the embryo develops can't consent to having her genes changed, and it could have a number of unintended side effects that researchers wouldn't be able to observe until many years later. These concerns inspired several scientists to write an op-ed, published in Nature last month, advising their colleagues to stop modifying embryos until they could hash out the ethical concerns.