Schizophrenia Genes Show Signs of Natural Selection
> 11/14/2007 2:14:37 PM

Esteemed game theorist and schizophrenic John Nash delivered a fascinating speech to the American Psychiatric Association in June, contending that many "bad" genes are actually evolutionarily adaptive. Given Nash's expertise in analyzing methods for gaining advantage, and the fact that he embodies the frequently encountered intersection of mental instability and genius, we reported on his speech with an openness to the possibility that schizophrenia and other mental disorders persist in the human population because they confer an evolutionary advantage. We were cautious about making any conclusions in that previous article because theoretical possibilities, however well formulated, are not sufficient to show that natural selection did choose schizophrenia. It is now possible to give this theory firmer support. A study in the most recent issue of the Proceedings of the Royal Society of Biological Sciences presents strong evidence that Nash's hypothesis is correct.

Some substantial evidence for the advantage of schizophrenia genes was garnered in a 2001 adoption study performed by Dr. Dennis Kinney. Dr. Kinney found that the biological children of schizophrenic parents were rated more creative by objective observers with no knowledge of their family history. Most of the creative children did not grow up to have the harmful symptoms of schizophrenia, suggesting that the diagnosis of schizophrenia may be on the extreme of a normally beneficial spectrum. Environment, or unfortunate combinations of independently advantageous genes, could destabilize an adaptive, if eccentric, brain structure.

Just because schizophrenia genes are advantageous does not mean that natural selection has consistently preserved them. However, the fact that 1% of every population in the world has schizophrenia, and that this rate is not decreasing, does make a circumstantial case for selection. Not content to rely upon this circumstance as proof, Dr. Bernard Crespi set up a study to track the 78 genes known to have links with schizophrenia. Two techniques were employed to establish whether positive selection occurred: determining how frequently schizophrenia genes are passed to future generations, and determining the percentage of conserved mutations that actually change the protein structure. The first technique found that schizophrenia genes are passed on in a pattern so strong that positive selection is likely. The second technique found that the ratio between protein-changing mutations and unimportant changes is very high for schizophrenia genes, meaning that these alleles serve a vital purpose rather than chance.

While the two genetic tests above are not infallible, they combine with theoretical models and family studies to create a convincing explanation for the prevalence of schizophrenia. This explanation cannot alleviate the suffering of the thousands of families dealing with a schizophrenia diagnosis, but it can give them an understanding of their suffering as the flip-side of a beautiful coin, a (perhaps too-costly) tradeoff for creativity.

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