Schizophrenia in an Evolutionary Perspective

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SCHIZOPHRENIA IN AN EVOLUTIONARY PERSPECTIVE JOHN S. ALLEN and VINCENT M. SARICH* Introduction Schizophrenia is at once one of the most fascinating and frustrating aspects of the human condition. The "schizophrenia problem" has been studied by physicians, psychiatrists and psychologists, neurologists, epidemiologists , sociologists, cultural anthropologists, geneticists, and biochemists . Although some claim that schizophrenia has a recent origin in human populations [1, 2], it is generally accepted that schizophrenia has existed throughout human history [3, 4]. The overwhelming majority of workers in the field now agree that schizophrenia is a condition with a strong genetic component in its etiology: a schizophrenic genotype (or genotypes) exists. But no one would argue that the expression of the schizophrenic phenotype is dependent solely on the genetic factors; concordance studies in identical twins make it clear that ontogenic factors, involving both the genie and cultural environments, play an important role in the character ofthe expression of the schizophrenic genotype [5— 9]. Because of this fact—one that would, in varying degrees, apply to any behavioral condition—casting the debate in the form of a nature/ nurture argument trivializes it into barrenness at best, and into counterproductivity at worst. Although it is often said that schizophrenia occurs at a frequency of about 1 percent worldwide, it should be recognized that this figure is an The authors thank the NSF for the support ofJohn Allen through a graduate fellowship and the Sloan Foundation for a research grant to Vincent Sarich; and Dr. Lawrence Stark, who, in addition to making his laboratory facilities available, made constructive criticisms of the manuscript, as did Barbara Bowman, Nancy Scheper-Hughes, and Allan Wilson. In particular, they thank the many undergraduates in their anthropology classes at Berkeley who have, over the years, endured the changing thoughts which have culminated in this article and whose challenging and penetrating questions contributed so strongly to those changes in their thinking on the subject.»Department of Anthropology, University of California, Berkeley, California 94720.© 1988 by The University of Chicago. AU rights reserved. 003 1 -5982/89/3201-0595$01 .00 132 I John S. Allen and Vincent M. Sarich ¦ Schizophrenia average and that there is considerable interpopulational variation in schizophrenia prevalence [10, 1 1]. Indeed, it would be very odd for any low-frequency condition with genetic involvement to manifest itself at uniform rates in all human populations. In the case of schizophrenia, Eaton's review [11] shows that there is about a tenfold variation in point prevalence rates. Using the 1 percent figure as a guide, and given the reduced fertility of overt schizophrenics [12], it follows that the schizophrenic genotype is being maintained in human populations at a frequency far greater than mutation rates would allow. This suggests that schizophrenia poses an interesting evolutionary problem—a fact first recognized by Huxley, Mayr, Osmond, and Hoffer [13]. The Beginnings ofan Evolutionary Perspective Evolutionary biology may therefore provide one approach to solving some aspects of the schizophrenia problem. While it would be misleading to state that the evolutionary perspective has never been applied in the study of schizophrenia [12-19], it is fair to say that it has had little or no influence on the conventional thinking about schizophrenia. There are a number of reasons for this. First, most investigators in the field have quite understandably had a clinical, sociological, or cultural orientation , and in none of these areas is an evolutionary perspective either common or especially welcome. Clinical thinking is necessarily typological , and we note that the typological approach has provided only a limited understanding of normal human variation. Second, the biological and genetic bases of schizophrenia, prerequisite knowledge for evolutionary studies, have only been established relatively recently (and imperfectly—see [20] for an overview). Third, evolutionary thinking is often perceived more as a hindrance than a help in studies concerning the modern human condition. For example, Gottesman and Shields state: We agree . . . that it is not too helpful to rely on evolutionary theory in deciding among genetic models; we simply do not know enough about how any human behavior evolved. . . . Attempts at invoking evolutionary (pseudo-) explanations for either the origin or perpetuation of schizophrenia may be futile and useless, muddling the line of genetic...

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