A Chinese researcher claims to have created the world’s first genetically edited babies.

The scientist, He Jiankui of Southern University of Science and Technology in Shenzhen, said he altered embryos for seven couples during fertility treatments, with one pregnancy resulting so far.

He told the audience he had worked on 31 eggs and implanted two altered embryos in one woman through IVF. The health of both children would be monitored for the next 18 years.

Many mainstream scientists think it is too unsafe to try, and some denounced the Chinese report as human experimentation. The genetic editing of a human embryo carries significant risks, including the risks of introducing unwanted mutations or yielding a baby whose body is composed of some edited and some unedited cells.

The tool for gene editing, called CRISPR-cas9, makes it possible to operate on DNA to supply a needed gene or disable one that’s causing problems. It’s only recently been tried in adults to treat deadly diseases, and the changes are confined to that person. Editing sperm, eggs or embryos is different because the changes can be inherited.

If true, it would be a profound leap of science and ethics.