Schizophrenic symptoms are conceived as arising from inter-individual variability in the distribution of those fibres that connect asymmetrical regions of the hemispheres related to language. Language (a bihemispheric phenomenon) arose as a result of a genetic change that allowed the two hemispheres to develop with a degree of independence. One component, the phonological output sequence, became localised to the dominant hemisphere, interacting through the corpus callosum with other component functions, including the associated meanings, in the non-dominant hemisphere. Nuclear symptoms are a consequence of failure of segregation of these two functions. This failure is associated with abnormal connectivity between the hemispheres and relates particularly to those regions that are late developing and differ between the sexes.