A growing body of work suggests that cell metabolism — the chemical reactions that provide energy and building materials — plays a vital, overlooked role in the first steps of life. Introduction Each of us starts life as a single cell. To develop into a complex, multicellular being, that cell must divide, and then those cells must divide again, and again — and then these stem cells start to specialize into different types, with different destinies in our bodies. In the first week, our cells reac...