Possible genetic and epigenetic links between human inner speech, schizophrenia and altruism.

Unique mental abilities have been crucial for evolutionary success of Homo sapiens and for the development of his complex social organization. However, these abilities have also become a target for mental disorders which often result in a reduced fitness and in conflicts between the individual and the conventions of society. To account for this evolutionary maladaptation, we advance a new concept: that of "mis-exaptation", derived from SJ Gould and E Vrba's concept of exaptation. Mis-exaptation is a characteristic which, although it may confer positive effects in one field of activity, may reach an inappropriate degree of specialisation to have deleterious effects in that or in another field thereby leading to a decrease in fitness of the individual. This paper considers "inner speech" as an exaptation. Although inner speech is usually a positive aid to learning and reasoning, it may also favour the emergence of mental disturbances, such as the auditory hallucinations which are characteristic of schizophrenia. There is, nevertheless, a possible evolutionary value in mis-exaptational inner speech; two traits associated with the mis-exapted state would be altruistic behaviour and heightened creativity, the latter being over-expressed in relatives of schizophrenic patients. A possible solution for the evolutionary-genetic paradox posed by altruism and schizophrenia arising from mis-exaptation will be suggested in the light of a cryptic genetic repertoire. A selection of illustrative examples of each of these mental states is presented as they appear in the pages of the European literature. This article is part of a Special Issue entitled: Brain Integration.