Our brain is extremely complex, performing countless complicated processes that allow us to think, move and feel. This is only possible because of the enormous diversity of different cell types in the brain, each with a very specific function. Researchers at the Max Planck Institute of Neurobiology, together with an international team, investigated how this diversity arises. They established a method to analyze the developmental relationships of cell types in the mouse brain. Their results show that similarities in cell types are not a measure for the degree of relationship: Cells of similar cell types are often unrelated. Conversely, cells of very different types can share the same origin.