The evolution of multicellular organisms from simple, single-cell organisms was a pivotal turning point in the history of life. Many different lineages of organisms, including animals, independently evolved multicellularity. One advantage of multicellularity is that cells can be programmed to perform particular biological roles. However, in order to assign cells to a specific role or fate, genes within certain tissues need to be activated at precise times during development. This process, which is known as spatiotemporal regulation, is orchestrated by various regulatory genes, including transcription factors and cell-signaling molecules.