"Great wits are sure to madness near allied,” John Dryden writes, framing the common wisdom. This formulation appeals to those who want to explain diseases like schizophrenia on evolutionary grounds. Why would a gene for illness persist, if it did not confer benefit (on patients or their near relations) as well as harm? It may be that the underpinnings of psychosis, especially in mania, can have their uses, but research appearing in yesterday’s Science magazine (see simpler summaries here and here) shows how a disruptive mental illness might afflict a substantial number of people and yet not be associated with any adaptive advantage.
Scientists looked at 150 individuals with schizophrenia and a larger sample of controls and ran their genes through a screen to pick up differences. The researchers did not find clusters of common gene variants that would explain the disease. Instead, the method revealed a high frequency of idiosyncratic mutations in the genes of individuals with schizophrenia—rare variants, often miscoding for substances important in the development of the brain and nervous system. Virtually all these disruptive genes were different, one from the other. Patients whose schizophrenia was evident in childhood (studied in a separate arm of the research) were yet more likely to carry anomalous genes.
Probably there are other kinds of schizophrenia. Still, the sorts whose underpinnings were elucidated by the new method seem not to involve genes passed down and spread through the human race. Rare mutations can arise on the spot, in parents’ germ cells or in conception and early development; they may be transmitted for only a few generations. (Some parents of children with schizophrenia had variant genes as well.) Natural selection, over millennia, is not brought to bear on these genes; there is no reason to believe that they have been preserved for their utility. They arise and do their harm.
Some of the same scientists have made similar findings regarding autism.
We want to believe that so destructive a disorder as schizophrenia must have its compensations. In the individual case, it can; people manage to put disease to use. But taking the larger view, on occasion we need to face terrible truths: nature can be cruel.
A note, regarding the success of advocacy for those with mental illness: the Science researchers wrote the whole of their report without once using the word “schizophrenic,” whether as an adjective or a substantive. (Science’s summary article does refer to schizophrenics.) I should add that I am not a purist in this regard. I understand the argument that those who suffer an affliction should have the greatest say in framing the ways in which it and they are discussed. At the same time, since we have asthmatics and epileptics, not to mention tubercular and cardiac patients, I can see reason in the argument that schizophrenics and schizophrenic patients ought to be ordinary formulations serving the position that schizophrenia is an ordinary disease.
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