MedIcal Hypotheses (2002) 58(3), 244--248 C 2002, Elsevier Science Ltd. All rights reserved.

doi: 10.1054lmehy.2001.1504, available online at ht!p://Www.idealibrary.oom on

How shamanism and group selection may reveal the origins of schizophrenia

J. Polimeni, J. P. Reiss

Depanment of Psychiatry, Faculty of Medicine, University of Manitoba, 771 Bannatyne Ave., Winnipeg, Manitoba, R3E 3N4, Canada

Summary Schizophrenia, with its apparent genetic basis, persists despite demonstrating impaired fecundity. Although this has been considered paradoxical, a similar paradigm is observed elsewhere in nature. Honey bee colonies possess sterile task specialists whose presence can best be understood by the evolutionary principle of group selection. Group selection may be pertinent to human history and consequently schizophrenia could represent an ancient form of behavioral specialization. Shamanism and religion demonstrate some similarities to psychosis and may provide clues regarding the origins of schizophrenia. © 2002, Elsevier Science Ltd. All rights reserved.

INTRODUCTION

Evolutionary forces may have significantly shaped schizophrenia, however this possibility seems largely ignored by most researchers. Since evolution may be framed as the study of genes through time, any condition that possesses ancient roots and genetic underpinnings may be subjected to evolutionary principles. Schizoph­renia is likely a genetically based illness with an ancient history; therefore, an evolutionary perspective could be critical to its understanding. A few researchers have applied evolutionary theory to the study of schizophrenia and have consequently developed a variety of novel per­spectives (1,2). These new viewpoints have implications to basic science research and therefore could help eluci­date the physiological mechanisms of schizophrenia Other medical conditions such as sickle cell anemia, tha­lassentia and lactose intolerance are better understood only through our recognition of evolutionary principles (3-5). In this paper, we will consider evolutionary forces present in early man's environment and outline the pos­sible origins of schizophrenia.

Reoeilllld 11 April 2001 ACC8p/9d 16 August 2001

Correspondence to: Dr J. Pollmanl, 771 Bannatyne Ave., Winnipeg, Manitoba, R3E 3N4, Canada. Phone: +204 787-7949; Fax: +204787-7480.

244

There is almost no doubt that schizophrenia bas a significant genetic basis (6,7). Schizophrenia commonly aggregates in families (8,9). It is estimated that first-degree relatives of patients with schizophrenia have a 3-7% risk for schizophrenia, which is substantially higher than the risk of schizophrenia in relatives of control probands (10). Though familial patterns invite the possibility of genetic explanations, they do not prove genetic causation. Twin and adoption studies are necessary to bolster theories pro­pounding genetic factors. Adoption studies demonstrate increased risk of schizophrenia in hiologic relatives of schizophrenic adoptees (11-13). The major twin stud­ies have demonstrated consistent results; monozygotic zygotic concordance rates (~40%) have always been substantially higher than dizygotic concordance rates H4%) (14).

Schizophrenia appears to have ancient origins, although it must be conceded the evidence for this is not conclusive. Most authors suggest schizophrenia is not a recent phenomenon (15,16). Jeste's review of ancient writings, dating back to Mesopotamia, produced several descriptions of aberrant behaviors that closely resembled schizophrenia Gottesman's interpretations of historical accounts, however, led him to conclude there is no uneqUiVocal recorded evidence of the condition prior to the nineteenth century (17). Gottesman used strict modern diagnostic criteria as a threshold before making

The origins of schizophrenia: shamanism and group selection 245

the retrospective diagnosis of schizophrenia. TIris seems exceedingly strict since ancient recordings usually invo­ked magical or religious paradigms in their interpretation of bizarre behaviors.

Accurately dating schizophrenia is not currently possible - although a minimum estimate would likely correspond to the last wave of ancient migrations into Australia. About 60,000 years ago, Australian Aboriginals became separated from the rest of mankind and effec­tively isolated (18). Schizophrenia has been observed in Australian Aboriginals (19) and other remote populations (20). Because schizophrenia crosses all cultures in app­roximately the same frequency (21), its presence was likely well established before the formation of the oldest genetically isolated racial enclaves.

The first hypotheSiS unequivocally connecting evolu­tionary concepts to schizophrenia was published in 1964 by Huxley et al. (22). They identified two characteristics related to schizophrenia that were ostensibly incompa­tible unless subjected to evolutionary explanations. They reasoned that schizophrenia's relatively high prevalence of about 1 % could not easily be reconciled with its low fecundity rate. If persons with schizophrenia were having fewer progeny due to their illness, how was the disease being maintained in the gene pool? Also known as the 'schizophrenia paradox', several attempts have been made to solve this problem (1,2). We hope our hypotheSiS extends and refines these previous efforts.

Before proceeding, are the two assumptions embed­ded in the Huxley et al. question true? In other words, does schizophrenia have a 1 % prevalence and do schizo­phrenics demonstrate reduced fecundity? The incidence and prevalence of schizophrenia has been carefully studied in many distinct cultures throughout the world (20,21) and it consistently exceeds common mutation rates. A recent review of fertility and fecundity in schizo­phrenia confirmed the presence of reproductive deficits particularly in males (23). However, it should not be assumed that schizophrenia always conferred repro­ductive disadvantage throughout man's existence. Almost all studies demonstrating reproductive deficits in schizophrenia were devised within the last 50 years and there are no accurate fecundity rates from traditional societies. Although schizophrenia appears to be a dis­advantageous condition accompanied by reduced fecu­ndity, some uncertainty exists whether this is true beyond the last century.

SHAMANS, RELIGION AND SCHIZOPHRENIA

Similarities between schizophrenia and shamanism could provide clues related to the origins of psychosis. In tribal communities, shamans are believed to possess spiritual powers resulting in the ability to heal others and

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communicate with the world beyond. Various forms of shamanism appear to be universally present in all hunt­ing and gathering societies. Defining characteristics are controversial; some authors emphasizing the presence of voluntary trances whlle others noting involuntary 'spirit possession' as essential (24--26). Silverman was the first to make a detailed analytical comparison of psy­cholOgical function between acute schizophrenia and shamanism (27). He found little difference in several 'core psychological factors' but noted a significant con­trast in the cultural acceptance of aberrant behaviors. Silverman argued that the stigma and futility of men­ta! illness in Western cultures exacerbated psychotic symptoms.

Establishing psychological parallels does not prove two entities possess common origins. However, several other similarities exist which require exploration. For example, studies reveal that psychotic-like behaviors are a salient feature of shamanism:

Shamans are selected and trained through a variety of procedures and auguries, including having had invol­untary visions, having received signs from spirits, having experienced serious illness, having deliberately undertaken vision quests, and having induced trance states through a variety of procedures, such as hallu­cinogens, fasting and water deprivation, exposure to temperature extremes, extensive exercise (e.g., dancing and long distance running), various austerities, sleep deprivation, auditory stimuli (e.g. drumming and chan­ting), and social as well as sensory deprivation Their trance states are generally labeled as involving soul flight, journeys to the underworld, and/or transforma­tion into animals (28). (p. 19).

Contact with the supernatural world may be the essence of shamanism (29). Out of body experiences are con­sidered to be nearly universal (26).

It is believed that shamanism is at least 20,000 years old and was universally present in all traditional hunting and gathering groups. In complex societies, shamanism evolved into societal roles such as medicine man, diviner, witch doctor, medium and healer. These terms are sometimes classified under the general desctiption, magicoreligous practitioner. An analysis of 47 societies throughout the world since 1750 BC revealed that all possessed some form of trance-based magicoreligious practitioner (30). Therefore, a genetic role in shamanistic behavior must be considered.

Religion appears to have meaningful connections to both shamanism and psychosis, thus supporting the notion that all three phenomena could have common origins. Religious delusions are a common feature of schizophrenia For example, one study found significant

Medical Hypotheses (2002) 58(3), 244--248

246 Polimeni and Reiss

religious delusions or hallucinations io IS of 20 schizo­phrenic patients retrospectively sampled from a state hos­pital io Hawaii (31). Another study comparing symptoms of schizophrenia among African cultures, found religious delusions io over 60% of the 113 subjects surveyed (32).

In the anthropolOgical record, evidence of religion, along with art, emerges between 30,000-60,000 years ago (33). A belief io non-physical beings appears to be the most common feature of religions (34). Another frequent theme is the assumption that certaio people are espedally likely to receive supernatural messages from gods or spirits. Two essential poiots may be derived from these fiodings: (I) religious thinking resembles some forms of psychosis; and (2) the near universality of specific reli­gious thoughts imparts a potential genetic etiology upon religion.

The presence of universal characteristics, presumably related to common environmental challenges, generally suggests evolutionary adaptation. In rare situations, such as the use of fire or stone tools, the utility of the response is so obviously adaptive that it becomes consistently iocorporated ioto the cultural repertnire without being directly maiotaioed by genetic mechanistns. Sioce reli­gion, shamanistn and psychosis would not have likely been viewed as obviously adaptive, their availability may have relied on genetic primiog. At some pnint io man's existence, it probably became evolutionarily adaptive for human tribes to engage io spiritual ceremonies. Psychotic experiences io some iodividuals may have been essential to spearhead such rituals. A predisposition towards reli­gious thinking would have reioforced group participation.

A resemblance between schizophrenia and shamanism seems to be more easily observed io less technolOgically advanced societies. Among Aboriginal Canadians, remote northern communities are more strongly rooted to their hunting and gathering lifestyle than city-dwelling Abori­ginals. The clinical experience of both authors is that visual hallucinations and delusions iovolving possession of animal spirits are sometimes associated with Aboriginal Canadians from remote northern communities but rarely do these kinds of psychotic experiences originate io city dwellers. Similarly, a study of mostly schizophrenic and manic depressive patients from rural Zimhabwe found that angered ancestral spirits, evil spirits and witchcraft were frequently seen as primary causes of mental illness by the community (35).

Epidemiological characteristics of schizophrenia also demonstrate similarities with shamanism For example, the onset of schizophrenia io young adulthood and the iotensification of symptoms during periods of stress par­allels shamanism. The gender bias of males being affected more severely than females is also consistent. I.ast1y, schizophrenia's I % prevalence corresponds well to tribal population densities. Sioce the average size of hunting

Medical Hypotheses (2002) 58(3), 244-248

and gathering tribes is 150-180 iodividuals (36), a tribe would usually be ensured one psychosis-prone shaman.

Another ioteresting parallel between schizophrenia and shamanism relates to the apparent shared predis­position towards expetimentation with psychoactive substances. Schizophrenic patients abuse many psycho­active substances such as caffeioe, cigarettes, alcohol and marijuana significantly above community norms (37). The diversity of substances abused makes it difficult to pro­vide a unlfying mechanism to explaio the behavior. The desire to experience any altered state-of-mind may be the most parsimonious explanation for psychoactive substance use io both shamanistn and schizophrenia.

There are slight iocompatibilities between classic shamanism and modern schizophrenia. First, visions are characterized more prominently than auditory halluci­nations io the shamanistic literature, while the reverse is true io schizophrenia. Visions, however, usually present more dramatically than auditory hallucinations and therefore are less likely to be overlooked by ethnologists. Second, trance ioduction, while frequently described io shamanism, is not generally associated with schizoph­renia. Trance states are usually initiated voluntarily while psychosis is generally conceptualized as an iovoluntary phenomenon. vulnerability towards dissociation has not been established io schizophrenia and an ability to achieve hypnotic states has yielded conflicting results (38,39). Observer bias could be responsible for framing shamanistic psychotic experiences as altered states of consciousness. Alternatively, the paucity of trance-like states io schizophrenia could be a modern cultural artifact.

PHENOTYPE VERSUS DISEASE

The boundary between normal phenotypic expression and disease can be iodistioct and neither definition exclUsively precludes the other. For example, dwarfism is generally associated with disease, but the short stature of African Pygmies is likely an evolutionary adaptation (40). Evidence suggests that African Pygmies possess reduced numbers of growth hormone receptors io bodily tissues (41), however these phenotypiC deficits should not be considered disease. In sickle cell anemia, the degree of red blood cell sickling correlates with phenotypiC advantage agaiost malaria - further exemplifying the difficulty io distinguishing disease from phenotypiC advantage.

Schizophrenia is clearly a mental disorder with little adaptive benefit to the iodividual io Western culture, however, it may not completely represent a disease process. Although modern technology has shown neurophysiolo­gic and neuroanatomical differences between groups of schizophrenic patients and controls, no specifiC pathog­nomonic trait or mechanism has yet been Identified.

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The origins of schizophrenia: shamanism and group selection 247

Gliosis and other typical markers of degenerative pathol­ogy are missing (42). The paucity of sensory findings and modest effects on motor skills in such a dramatic condi­tion further challenges the classic disease model.

Similarities between some symptoms of schizophrenia and disease states such as delirium, dementia and tem­porallobe epilepsy may be the best evidence for disease in schizophrenia. Returning to the Pygmy example, short stature likely represents an adaptation to environmental cballenges rather than disease. If adaptive, incorporating traits usually associated with biological dysfunction may be the most expeditious evolutionary path for an organ­ism. The same parallel may apply to hallucinations and delusions; their association with disease states does not preclude the possibility that these 'symptoms' could be adaptive in other contexts.

GROUP SELECTION

The comparison between short stature in Pygmies and schizophrenia may not be completely analogous. Short stature in Pygmies affects an entire population while schizophrenia only affects a small subset. Evolutionary adaptation primarily functions at the level of the indivi­dual and consequendy successful traits tend to spread ubiquitously through populations. Schizophrenia's low frequency places its potential as an adaptive trait into question.

The evolutionary concept of group selection could provide an explanation supporting significant phenotypic diversity within a speeles. Some bighly cohesive speeles act like 'superorganisms' with selection pressures acting on the group as well as the individual. Honey bees, for example, utilize division of labor (i.e. queen, sterile worker castes), presumably to enhance effielency and effectively compete with other colonies (43). Task speelalization seems to be genetically influenced but the specific mechanisms are largely obscure (44,45). Of significance is the presence of sterile worker bees, wbich suggests some specialists are exempt from individual selection pressures.

Humans and honey bees share two characteristics generally not found in other species; complex commu­nication and altruism. These behaviors have not been easily integrated into evolutionary models of individual selection. Wilson and Sober have argued that group selection is an important force to consider in human evolution (46): 'Since humans have lived in small groups throughout their bistory, it is reasonable to expect the evolution of psychological mechanisms that cause them easily to become "team players" in competition with other groups'. This interesting formulation entertains the pos­sibility of psycholOgical specialization among humans, for example, leaders and followers (46,47).

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We propose to extend this line of reasoning and sug­gest human populations could possess specific cognitive specialists. Analogous to the differentiation observed in honey bees, schizophrenia could have represented a form of behavioral specialization In hunting and gathering societies, individuals with schizophrenia-like symptoms may have been instrumental in initiating and maintaining spiritual ceremonies. Rituals about supernatural phe­nomena would likely foster group cohesion and therefore be evolutionarily adaptive. The dramatic quality of hal­lucinations and delusions would cast an indelible imp­ression on others, reinforcing the notion of supernatural forces. Poverty of thought, a pervasive feature of schizo­phrenia, would attenuate lOgical analyses of discrepant information and facilitate delusional thinking. Other negative symptoms of schizophrenia such as social with­drawal, avolition and alogia would erode basic human qualities, thereby giving credence to the belief that the afflicted individual was truly a vebicle of supernatural phenomena.

In addition to schizophrenia, other psychiatric condi­tions such as obseSSive-compulsive disorder or bipolar disorder may represent alternate forms of ancient cogni­tive specialization. For example, obsessive tendencies may have been valuable for meticulous tool construction or maintenance of campfires. These characteristics would not necessarily have to be present in the majority of individuals for the group to derive benefit.

CONCLUSION

There are several features related to schizophrenia that are ostensibly incompatible. The persistence of a bigh­prevalence genetically based disease that seemingly demonstrates impaired fecundity appears paradoxical. Evolutionary principles may be essential to the solution of the 'schizophrenia paradox'. Specialization related to group selection may be an integral component of human evolution and could help explain the presence of see­mingly disadvantageous traits in a subset of the general population The benefits of shamanism and religion to tribal groups, through their possible association with psychosis, may shed light on the origins of schizophrenia.

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