Human embryos start as a tiny mass of cells that are all the same. The first step in growing from a homogenous ball of cells into a complex individual with distinct organs and tissues is for the cells to divide into distinct populations. Scientists at the Gladstone Institutes have modeled this first step in human development in a laboratory with the goal of better understanding how organs form. With this knowledge, they hope to create more authentic organoids that can be used for drug testing, disease modeling, and potentially even transplantation.