From the moment of fertilization, building a human body involves a series of choices where cells generated by cell division must elect which of the myriad types of cell they will become. How does this decision occur? New research from Alice Moussy and colleagues of the Ecole Pratique des Hautes Etudes, Genethon and ENSLyon in France suggests that fate decision is not a unique programmed event, as was believed, but the outcome of a very dynamic process. The study, publishing July 27 in the open access journal PLOS Biology departs from the view that cell differentiation follows step-by-step instructions.