Think about the moment you were conceived. No, not that part! I mean, think about how, when you were conceived, you were made up of just one cell. Eventually that cell divided into two cells, and then each of those divided, making four in total. When cells divide, they try to create perfect copies of themselves. Yet, as an embryo grows, its cells differentiate. They turn into blood cells and bone cells and back-of-the-eyeball cells, each with a different shape and function. Turing was interested in how such changes happen. He came up with a model that biologists consider an important way of thinking about differentiation, while acknowledging the model has its "successes and pitfalls." Turing's paper about the idea has been cited more than 8,000 times.