Balancing selection--no answer for schizophrenia

Many have asked why genes that cause such a serious disease persist, and a number of evolutionary hypotheses have been inspired by the kind of balancing selection that explains the persistence of genes that cause sickle cell disease. A new article by Adriaens debunks such hypotheses. He offers a nice review of studies about the reproductive success of people with schizophrenia, although I think he discounts excessively the evolutionary significance of a 50% fitness decrease for male schizophrenics.

It seems to me that he is absolutely right, however, to point out data that undermine hypotheses based on covert benefits of schizophrenia genes. He generalizes about evolutionary psychiatrists as if they are not only all in one category, but as if they all think the same things. This is especially surprizing given his emphasis on the mistake of assuming that schizophrenia is a natural category. It is so important to criticize hypotheses, not people or groups.

There is much additional useful in his paper, especially his outline of evolutionary reasons why the genetic factors in schizophrenia will be much more complex than we have imagined. This all fits very nicely with other reports this week about the genetics of schizophrenia I do think, however, that we do need to ask why such a highly heritable devastating disorder persists. Balancing selection is not likely. It could be just that new mutations happen. But I think that the high heritability has kept attention focused on the level of the gene, when the problem may well be in constraints and trade-offs at a higher level. See a previous post for more on this.