6 key dilemmas as human embryo models get ever closer to the real thing

Researchers are racing to engineer highly realistic human embryo models using stem cells in the lab. Some of the newest models are now so similar to real human embryos that it’s unsettling even if also exciting in terms of research potential.

One core goal for embryo modeling is to better understand early human development and related diseases. In theory, the models could also become a valuable source of tissues for clinical use as an alternative to standard organ transplantation.

While the models will catalyze new, unique research advances, biologists disagree about key issues related to them, including how long it should be OK to grow these human embryo-like structures in the lab. Recently, a group of experts called for a hard-stop eight-week limit and called for most such research to stop at four weeks, but others are likely to push back. There are many other disagreements and dilemmas — and how we resolve them, or don’t, will determine the course of a potentially groundbreaking field.

I’ve heard colleagues say that they hope that embryo model research might be done without...