Designer Babies Are Here. What's the Next Edit?

Jiankui He stunned the world this week when a report revealed he had edited genes in human embryos aiming to make people resistant to HIV infection. So far, two children, twin girls named Lulu and Nana, are said to have been born with altered genomes.

The Chinese scientist’s work crossed a line that many have feared and some have dreamed of: the creation of designer babies engineered for certain enhancements.

Editing genes in embryos is hugely controversial because the changes can be passed along to future generations. You can imagine, for instance, using gene editing to wipe out a genetic disease in an entire family tree. This is what makes altering DNA in sperm, eggs, or embryos — known as germline editing — so powerful. But if something were to go wrong, like cutting an unintended place in the genome, the resulting child could have health problems or introduce new, potentially harmful mutations into the gene pool, where they could be difficult to eradicate. That risk has made the scientific community wary of using gene editing in this way.

The floodgates are open, and...