Letters to the Editor
Re: Evolutionary Perspectives on Schizophrenia
Dear Editor:
In their recent paper, Dr Polimeni and Dr Reiss discussed how schizophrenia may fit with the theory of evolution (1). They considered whether schizophrenia may be a disadvantageous byproduct of human brain evolution or whether there may be individual advantages or advantages for kin.
Another possibility may be that schizophrenia continues to exist, despite the obvious disadvantages to its carriers, because these individuals live in a protected environment. This argument is similar to reasoning that pertains to why unusual species exist, first discussed by Darwin in the Origin of Species.
The genera Ornithorhynchus (platypus) and Lepidosiren (lungfish), for example, would not have been less aberrant had each been represented by a dozen species, instead of as at present by a single one, or by two or three. We can, I think, account for this fact only by looking at aberrant groups as forms which have been conquered by more successful competitors, with a few members still preserved under unusually favourable conditions (2).
Could this also be true for a person with schizophrenia? For many years, patients with this condition were protected in asylums. Now, they are protected and treated with antipsychotic medications. Surely, the effects of natural selection are being offset by the artificial selection that humans effect in caring for their sick. I am not saying that caring for the sick is wrong, but the more we do it, the more disease we will preserve, in an evolutionary sense. Thus, owing to our compassion and ethics, we guarantee that schizophrenia and other diseases with genetic components will exist for eons, despite their evolutionary disadvantages.
Likewise, consider that natural selection usually takes place over a very long time. If a condition does not confer a large enough disadvantage in an evolutionary sense, it could be perpetuated until the rest of the species has a new advantage that is selected. Given that our species, Homo sapiens, is thought to have evolved approximately 200 000 years ago (3), this could be tens or hundreds of thousands of years more. It may be that humans as a species have not been around long enough for schizophrenia to become an extinct disease.
Further, although schizophrenia is associated with reduced fertility rates, it is possible that, compared with the recently relatively low fertility of the rest of humankind (4), it is not low enough to eradicate the disease.
References
1. Polimeni J, Reiss J. Evolutionary perspectives on schizophrenia. Can J Psychiatry 2003:48:34–9.
2. Darwin C. On the origin of species by means of natural selection. 1st ed. London: John Murray; 1859.
3. Leakey R, Butzer K, Day M. Early Homo sapiens remains from the Omo River region of Southwest Ethiopia. Nature 1969:222:1132–8.
4. Martin J, Hamilton B, Ventura S, Menacker F, Park M. Births: final data for 2000. Natl Vital Stat Rep 2002;50(5):1–101.
Jamie Karagianis, MD, FRCPC
St John’s, Newfoundland
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