For decades, scientists from around the world have been in agreement about one ethical rule: Don’t try to change genes in sperm, eggs or embryos.

Trying to use genetic engineering to fix diseases in the cells of our body, like cystic fibrosis in the lungs or macular degeneration in the eye — that’s fine. A lot of work on this kind of gene therapy has been going on around the world for many years. But those genetic changes, whether they work or not, are not passed on to future generations. Trying to change the heredity of our kids and grandkids, either to fix diseases or to make “enhanced” children, was again and again declared off limits by scientists, doctors and many others.