Speciation in colour: a textbook example of evolution in action The cichlid fish of African lakes are textbook examples of rapid speciation but the mechanisms involved remain elusive. Observations of the cichlids in Lake Victoria now demonstrate the ecological and molecular basis of divergent evolution of the visual system (seen as divergence of vision genes, male coloration and female preferences) leading to speciation by sensory drive through interacting natural and sexual selection. The sensory drive hypothesis predicts that divergent adaptation in sensory and signalling systems to different environments can cause premating isolation between populations. As well as providing clear evidence that speciation can occur through sensory drive without geographical isolation, this work provides a mechanistic explanation for the collapse of cichlid fish species diversity during the anthropogenic eutrophication of Lake Victoria. On the cover, the colourful cichlids Pundamilia nyererei and Pundamilia pundamilia, as well as a wild intermediate (top) with the light spectra from different water depths in the background. [Article p. 620; News & Views p. 601; www.nature.com/podcast] Cover images: Ole Seehausen & Inke van der Sluijs.