So when a Chinese team revealed last month that it had used a new laboratory technique to alter a gene in human embryos, it set off an urgent debate over the ethics — and wisdom — of tinkering with the most basic building blocks of life.

The technology makes genetic manipulations that were theoretical in the past seem easy to achieve — and soon.

If scientists figure out how to do it in a way that's safe for patients, gene editing could produce tremendously beneficial medical treatments. The Chinese researchers, for instance, were trying to repair a defect that causes beta thalassemia, a potentially fatal blood disorder.