AbstractSensory organs are specialized to receive different kinds of input from the outside world. However, common features of their development suggest that they could have a shared evolutionary origin. In a recent paper, Niwa et al.1 show that three Drosophila adult sensory organs all rely on the spatial signals Decapentaplegic and Wingless to specify their position, and the temporal signal ecdysone to initiate their development. The proneural gene atonal is an important site for integration of these regulatory inputs. These results suggest the existence of a primitive sensory organ precursor, which would differentiate according to the identity of its segment of origin. The authors argue that the eyeless gene controls eye disc identity, indirectly producing an eye from the sensory organ precursor within this disc. BioEssays 26:825–828, 2004. © 2004 Wiley Periodicals, Inc.