In his target article Crow (2000a) summarized the hypothesis that a genetically based shift in cerebral dominance (CD) favoured the development of language and, perhaps, consciousness. On the basis of Crow's thesis one can hypothesize that a disorder like a psychosis, which in its milder form could favour a creative use of the language, would also contribute to strengthen the adaptive potential of a gene which per se increases the use of language. Propensity to develop a psychosis can be conceived as a 'hitch-hiker' allele which confers no fitness advantage per se, but which endures because it is linked to abilities (linguistic skills) that are important for survival. The main carrier would be the gene producing cerebral dominance, and the subsequent improved use of speech and language.
2. Comparative evidence shows that asymmetries in the human cerebral area controlling language are missing in the chimpanzee, one of the species closest to man on a genetic level (Buxhoeveden & Casanova, 1999). Even the right hand preference, shared by about 90% of humans, is absent in chimpanzees (Marchant & McGrew, 1996).
3. According to Crow, speciation of homo sapiens should be happening through the diffusion among hominids of a gene which determines the lateralization of cerebral functions. This gene should be linked to the Y chromosome and subject to mate selection in males by females. Briefly: the gene would favour better communication between sexes, thus producing a a female preference for its male carriers. Better communicative skills are indeed likely to favour the acquisition of resources and would also improve relational and affective interchanges between sexes.
4. Annett (2000) objected that the typical pattern for cerebral dominance is variable and not universal. About one person in five is expected not to carry the hypothesized gene of typical cerebral dominance. Hence, according to Annett, the speciation of homo- sapiens could not have occurred on the basis of cerebral dominance for language. Annett is probably right that the gene for CD would favour speech rather than language. Nevertheless, the spreading of a gene which favours adaptation to the environment does not necessarily need to be universal.
5. Wilson and co-workers (1994), in their revision of the hypothesis of evolution by groups, illustrated that a gene conferring some advantage to a group can favour the success of the group over competing groups even if the carriers are not the majority of individuals in that group. If a group obtains some advantage from the presence of individuals with a mutant gene, this advantage extends to the other members of the group lacking the gene, because they benefit, as members of the group, from better access to resources for survival and reproduction produced by the carriers. Group selection has often been thought to favour traits that are individually disadvantageous but evolve because they benefit the larger group.
6. Doubtless better use of speech and language favours cohesion within a group, and also favours the organization of activities for acquiring and maintaining of the resources. Any further mutation which would increase this already improved linguistic skill will be fixed in the population, since the new mutation strengthens the adaptive potential of the first mutation.
7. Crow writes that a characteristic of language is the arbitrariness of the associations between signs and meaning. Two form of psychosis, schizophrenia and manic-depression, are characterized by a peculiar use of language. In schizophrenia there is a trend toward the creation of new words or the uncommon use of old terms (neologism), which can in extreme cases give rise to a complete loss of any communication (salad of words) (Arieti, 1974). In manic-depression, in the hypomanic phase or in the slight mania, there is sometime a playful, articulate and poetic use of language, which can yield particularly creative results (Goodwin & Jamison, 1990).
8. Many studies have explored the links between creativity and mental illness (Preti & Miotto, 1997a; 1997b). More than two millennia earlier, in the fragment known as "Problemata XXX," Aristotle, or a disciple of his, raised the question of why the vast majority of the eminent people are afflicted by "melancholy," i.e. suffer from a mental disorder. The image of genius as a result of madness has been repeatedly described in the history of the western world, being codified during the Renaissance in the figure of the melancholic genius afflicted by Saturnian features, and resurfacing during Romanticism in the figure of the deracinated artist. The Italian anthropologist and criminologist Cesare Lombroso (1891) was among the first to apply a less anecdotal method to the investigation of the relationship between the creative gift and the risk of a mental illness, offering an answer that is nevertheless the positivistic version of the romantic myth. Most studies performed in the positivistic era in order to either confirm or refute Lombroso's hypothesis rest on biographical evidence (Richards, 1981). This raises the suspicion that these studies claiming a higher prevalence of psychopathologies among creative or eminent people were biased by overexposure. Despite these reservations, even later studies, using specific nosographic categories and direct confrontation with the candidate through interviews and inventories, reported a higher prevalence of mental disorders among gifted people than among the general population ((Preti & Miotto, 1997a; 1997b; Waddell, 1998). This increased risk of mental disorders among creative people seems particularly high among poets and writers, the artisans of language, who bear a significantly higher risk of death by suicide (Stack, 1996; Preti & Miotto, 1999).
9. The evidence of a link between creativity and mental illness is far from being conclusive, and even the direction of the link still needs to be determined(Waddell, 1998). However, on the basis of Crow thesis one can hypothesizes that a disorder like a psychosis, which in its milder form could favour a creative use of the language, would also help strengthen the adaptive potential of a gene which per se increases the use of language.
10. Maladaptive mutations for survival and reproduction, which is what psychoses are, could be preserved in the population if they had some peculiar adaptive potential which compensated for the disadvantages, as the sickle-cell anemia model illustrates (Huxley et al, 1964).
11. We hypothesize that the genes which increase the risk of psychosis are maintained in the human population as a 'hitch-hiker' allele. Propensity to develop a psychosis can be conceived as a 'hitch-hiker' allele which confers no fitness advantage per se, but which endures because it is linked to abilities, linguistic skills, that are important for survival. The main carrier would be the gene producing cerebral dominance, and the subsequent improved use of speech and language. One might expect and the opposite pattern in schizophrenics. Some studies do show a link between schizophrenia and impaired, CD (Crow, 2000b). This could be the result of early developmental brain damage (McNeil, 1995; McNeil et al, 2000; Preti et al, 1998), or of the absence of the gene for CD (Annett, 1997; Crow, 2000a; 2000b).
12. Crow's hypothesis offers a speculative scenario with testable potential. If a gene for CD is ever isolated, it may be possible to test the speculation that psychoses are linked to it.
Annett, M. (1997) Schizophrenia and autism considered as the product of an agnostic right shift gene. Cognitive Neuropsychiatry, 2, 195-214
Annett, M. (2000) No homo speciated on cerebral dominance. PSYCOLOQUY 11(020) ftp://ftp.princeton.edu/pub/harnad/Psycoloquy/2000.volume.11/ psycoloquy.00.11.020.language-sex-chromosomes.2.annett http://www.cogsci.soton.ac.uk/cgi/psyc/newpsy?11.020
Arieti, S. (1974) Interpretation of schizophrenia. Basic Books, New York
Buxhoeveden, D., & Casanova, M. (1999) Comparative lateralisation patterns in the language area of normal human, chimpanzee, and rhesus monkey brain. laterality (in press)
Crow, T.J. (2000a) Did Homo Sapiens Speciate on the y Chromosome? PSYCOLOQUY 11(001) ftp://ftp.princeton.edu/pub/harnad/Psycoloquy/2000.volume.11/ psyc.00.11.001.language-sex-chromosomes.1.crow http://www.cogsci.soton.ac.uk/cgi/psyc/newpsy?11.001
Crow, T.J. (2000b) Schizophrenia as the price that homo sapiens pays for language: a resolution of the central paradox in the origin of the species. Brain Research Reviews, 31, 118-129
Goodwin, F.K., & Jamison, K.R. (1990) Manic-Depressive Illness. Oxford University Press, New York
Huxley, J., Mayr, E., Osmond, H., Hoffer, A. (1964) Schizophrenia as a genetic morphism. Nature, 204, 220-221
Lombroso, C. (1891) The Man of Genius. (original edition in Italian) Walter Scott, London
Marchant, L.F., & McGrew, W.C. (1996) Laterality of limb function in wild chimpanzees of Gombe National park. Journal of Human Evolution, 30, 427-443
McNeil, T.F. (1995) Perinatal risk factors and schizophrenia: selective review and methodological concerns. Epidemiologic Reviews, 17, 107-112
McNeil, T.F., Cantor-Grace, E., Baher, I. (2000) Obstetric complications and congenital malformation in schizophrenia. Brain Research Reviews, 31, 166-178
Preti, A., & Miotto, P. (1997a) The contribution of Psychiatry to the study of creativity. MIND II, Dublin, Ireland http://www.compapp.dcu.ie/~tonyv/MIND/antonio.html
Preti, A., & Miotto, P. (1997b) Creativity, evolution and mental illnesses. Journal of Memetics - Evolutionary models of information transmission, 1 http://www.cpm.mmu.ac.uk/jom-emit/1997/vol1/preti_a&miotto_p.html
Preti, A., Miotto, P., Zen, T. (1998) Perinatal complications, genetic risk and schizophrenia. Acta Psychiatrica Scandinavica, 97: 381-383
Preti, A., & Miotto, P. (1999) Suicide among eminent artists. Psychological Reports, 84: 291-301
Richards, R.L. (1981) Relationship between creativity and psychopathology: an evaluation and interpretation of the evidence. Genetic Psychology Monographs, 103: 261-324
Stack, S. (1996) Gender and suicide risk among artists: a multivariate analysis. Suicide & Life-Threatening Behavior, 26: 374-379
Wilson, D.S., & Sober, E. (1994) Re-introducing group selection to the human behavior sciences. Behavioral and Brain Sciences, 17, 585-608 http://www.cogsci.soton.ac.uk/bbs/Archive/bbs.wilson.html