We question some aspects of Eric Lander and colleagues’ proposed moratorium, although — like most in the bioethics and science-policy communities — we are also deeply concerned about experimentation with human germline editing (see Nature 567, 165–168; 2019).

For example, the authors emphasize that they do not mean a permanent ban. On the basis of our extensive analysis of other moratoriums aimed at human reproduction in the United States, however, we have found that what started as a temporary pause can quickly become stuck (for details, see R. A. Spivak et al. J. Law Health 30, 20–54; 2017 and R. A. Spivak et al. J. Health Biomed. Law 14, 5–26; 2018). The Dickey–Wicker Amendment, which prohibits federal funding for research in which human embryos are “knowingly subjected to risk of injury or death greater than that allowed … in utero” and has never been seriously revisited, is a cautionary tale.

Lander et al. further argue that genome editing is unnecessary because couples at risk of transmitting a heritable disease already have safe ways to avoid doing so. However, that can require third-party sperm or ova, which might not be available in some countries. Even if gametes are available, there is still the ethical question of whether a couple’s interests in having genetically related children should give way to state regulation (see also H. König Nature 568, 458; 2019).

Also, countries that shape their own variants of the ban would have to decide whether to forbid citizens from going abroad to access such technologies. Patients have, for example, gone to other countries for mitochondrial replacement therapy (see I. G. Cohen Indiana J. Glob. Leg. Stud. 25, 439–462; 2018).