Those who as adults will be admitted to a psychiatric ward with a psychotic illness can be distinguished (on the basis of group differences) from others by their behaviour and academic performance at he ages of 7 and 11 years. Pre-schizophrenic boys are anxious and hostile towards adults and peeres at the age of 7 years and show poor concentration. By age 11 years these boys are also rated as depressed, and pre-schizophrenic girls as depressed and withdrawn. Pre-affective psychotic boys show minor changes (for example an increase in hostiliti and restlessness) at age 7 years, although these features are not obvious at age 11 years. Abnormalities that in some respects resemble those in pre-schizophrenic boys are present at age 11 years in a group of females who will be admitted to psychiatric units with non-psychotic diagnoses by the age of 28 years. Academic impairments (including speech and reading difficulities) at ages 7, 11 and 16 years are more severe in pre-schizophrenics than in the other groups. Schizophrenics-to-be are slow to develop contininence and show poor coordination and vision at age 7 years, and are rated clumsty at age 16 years. Psychosis reflects a disturbance of spects of central nervous system function that are time-dependent and in certain respects gender specific. It is argued that the psychoses represent extremens of variatiion in agene (or genes) that differs between the sexes and controls the timung of development of the two ceraral hemispheres. The diversity associated with this gen(s) may be maintained by selective pressures that have led to the neotenic process of endophalisation in humans and theevolution of language.