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

The lab-engineered models give scientists a look at human development beyond the first week

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

A 6-day-old embryo model from Jacob Hanna’s lab in Israel has structures akin to ones found in human embryos 12 days after fertilization. Those structures include a ball of cells (top, purple) that resemble the layer that forms the body, and a hollow circle of cells (bottom, blue) mimicking the yolk sac, all surrounded by a layer of cells similar to a placenta-forming layer in human embryos.

Jacob Hanna

Some newly reported clumps of cells growing in lab dishes have been hailed as the closest things to human embryos that scientists have ever made in the lab.