During sympatric and parapatric speciation the diverging populations maintain geographical contact throughout the speciation process. In theoretical models an isolating mechanism, such as assortative mating, is usually needed to obtain genetic separation of populations in contact. We simplified the visual appearance of the crows that occur in the crow hybrid zone in Europe, the carrion crow, Corvus corone, hooded crow, C. cornix, and hybrid crows. We then mimicked the sexual imprinting process by training artificial neural networks to separate their own type from the other two. The network learned pure phenotypes faster and better than the hybrid patterns showing that already at the receptor level there may be signal reception properties that will make speciation under sympatric and parapatric conditions possible. Thus, mate choice preference can be a self-emerging nervous system property not requiring evolutionary selection. (c) 2006 The Association for the Study of Animal Behaviour.