Hox genes are a group of regulatory genes that control the timing and route of development. They’re a bit like lighting engineers at a concert; they control when and where a light goes on, how strongly and for how long it is switched on. They all cluster together on the genome and play a major role in the development of animal segments with different Hox genes being expressed in different segments. Hox gene evolution played a big role in the diversification of these segments. But how do we know this?