While other animal embryos grow outside the mother, their embryonic cells can get right to work accepting assignments, such as head, tail or vital organ. By contrast, mammalian embryos must first choose between forming the placenta or creating the baby. New research has pinpointed two proteins that are the keys to this decision making. The process of assigning cells to placenta or baby is important because that is when pluripotent cells are made. These adaptable pluripotent cells are critical to stem cell research.