Human embryo replicas have gotten more complex. Here’s what you need to know

A model of a human embryo against a black backdrop. The model has ane exterior ring dotted with bluish light clumps. Wtihin is an oval-shaped purplish blob of cells with orange running through it. Below that are long bluish structures, also with bright orange and white running between cells

Human embryo replicas have gotten more complex. Here’s what you need to know

Lab-engineered human embryo models created from stem cells provide a look at development beyond the first week. But they raise ethical questions.