Phylogenetic precursors of psychiatric illness: A theoretical inquiry

Phylogenetic Precursors of Psychiatric Illness: A Theoretical Inquiry Horatio

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Vol. 20, No. 3 (May/June),

1979

275

276

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evolved to cope successfully with ecologic factors that pose significant biologic threats.3 The race-I.Q. question, disregarding its moral and political aspects, may be taken as an example of the difficulty of disentangling biologic and cultural influences on behavior among peoples of one society who speak the same language and share basic ideologic premises. When physically separate groups having distinctive histories and traditions are studied, the problem of establishing the possible sources of human differences is compounded for, although the genetic systems of the groups in question may be sharply different, the problem of specifying the many influences that culture may have becomes far more complex. One is forced to conclude that many “biologic versus culture” questions are not appropriate and those that are, necessarily are restrictive and need to be stated precisely. An important contemporary definition of culture, and one that we shall adopt here, involves a group’s system of social symbols and their meanings.“ A sine qua non of human action is that it is expressive and social symbols figure importantly in what such actions mean and the role they play in behavior. Since the meanings of social symbols can only be inferred from a gruop’s mode of life, this prompts a definition that will be used in the paper: Culture refers to the symbolic properties inherent in a group’s social and cognitive behavior. This definition means that one needs to distinguish among different categories of behavior. Accomplishing this will be useful in subsequent discussions in this paper. By social behaviors one can refer to activities such as gestures, demeanor, facial displays . and simple or coordinated actions (including the performance aspects of language and speech) that are viewed in an interindividual context. The appropriate performance of a social role belongs in this category of behavior. As summarized in detail elsewhere, social behavior is a category that both social and biologic scientists have fruitfully applied to human and infrahuman gruops. This category of behavior has been equated with the functioning of the frontal system of the brain.5 Behaviors that reflect internal discriminative processes, and that are correlated with observable social behaviors, are here termed cognitive. They often imply learning and, in humans, the internalization of shared symbols and rules. Each category of behavior (i.e.. social and cognitive) logically implies the other. Cognitive behaviors embrace such things as thinking, perceiving, interpretation of actions, rules for expressing actions, remembering, and problem solving. Although cognitive implies conscious or deliberate. it has to be acknowledged that many cognitive behaviors cannot easily be judged in this fashion. The problem of volition and awareness will not be tackled directly in this paper though facets of this are discussed later. An individual’s capacity for and creative use of language will be viewed as a component of cognitive behavior. A third category of behavior can be singled out analytically and will be termed motor behavior. In this category are placed sequences of more or less coordinated muscular contractions viewed physically. Reflexes, posture, muscular tone, and the coordination of finely-graded muscular contractions, when viewed purely as physical phenomena. constitute motor behaviors as do covert

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277

ILLNESS

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members and of comembers have generally been explained in terms of ideas of social bonding, social support, dependence, and ultimately parent-offspring interactions.15 These types of behaviors are integral to the idea of disease when we use it to qualify happenings in human groups, but similar behaviors in animal groups seem not to warrant the idea. The material reviewed thus far suggests that when the idea of disease is used in general biology, it can mean a number of different sorts of things, some of which are not necessarily implied when the idea is used in a human-practical framework. Moreover, states of disease in animals can be linked to changed social behaviors, some of which can elicit support from comembers; however, these behaviors are not necessarily included in the meaning of disease when it is applied to animals. It should be emphasized that the synthetic theory of evolution has available many ideas whose meanings embrace much of what one has in mind when using the idea of disease. Ideas such as organism, development, genetic variation, fitness. natural selection, and environment seem sufficient to explain much of the phenomena linked to disease. The explanatory power of these ideas and the seemingly motivated and expressive aspects of behaviors linked to disease in humans are, thus, factors that seem to weaken the idea of disease when used in a general frame of reference. One may infer from this discussion that a general definition that provides one with conditions for using the idea of disease in a human-practical as well as in a general biologic frame of reference may not be possible. One needs to make explicit the specific kinds of phenomena that require explanation and develop guidelines for using ideas with reference to them. One suggestion is to give the general idea of disease alternative meanings. i6*17The idea of disease as illness may be used to signify purely behavioral changes. In a general anthropologic sense, it is a set of behaviors, judged as undesirable and unwanted in a culture, which are considered as having medical relevance. It is changes in the behavioral sphere in the form of symptoms that initially concern members of a social group and lead them to seek help. Relief from these unwanted behaviors is very often the end point of treatment. Disease as illness, then, may serve as a suitable idea for explaining social and cultural facets of medicine that have special significance to human groups. In designating behavioral changes, illness begins to have a communicative function, tending to express need and, in turn, to elicit support. Illnesses constitute the raw data that societies use in order to develop theories and institutions for coping with medical problems.16*” An idea or concept is also needed in general biology to describe an emergent set of changes in the internal structures and processes of living forms that underlie and account for their failure to adapt. What can be termed a biomedical disease seems useful here. In referring to abstract and physical (e.g.. chemical) structures and processes that underlie and account for failures in adaptation and reproduction, the biomedical idea of disease can be used to describe organisms of any type. The fact that it is used with reference to all types of living forms and, moreover, denotes physical changes in the apparatus, means that the idea of a biomedical disease does not directly refer to social cultural phenomena. Hence, it is less central to discussions about human problems and values. The biomedical disease may be especially relevant for

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explanations about biologic evolution whereas the social medical illness seems relevant for explanations about the complementary process of social evolution. SOCIAL AND COGNITIVE EVOLUTIONARY

BEHAVIOR IN A GENERAL FRAMEWORK

Behaviors associated with a psychiatric illness such as schizophrenia are ordinarily thought of as requiring capacities that are said to be quintessentially human. Common descriptions of the symptoms of schizophrenia imply the existence of human language, of ability to symbolize, and also mentalistic notions such as feelings and self-awareness. A formulation of psychiatric illness as psychopathology (i.e., as mental and intrinsically human) creates a special problem for one wishing to clarify the question of phylogenetic precursors since one is now dealing with organisms in which mental phenomena are controversial. For heuristic reasons. we have adopted a modified behavioristic perspective in which human (or humanoid) behavior is equated with cultural, which in turn we have defined as embracing social and cognitive behaviors. This perspective allows one to avoid handling psychiatric illness purely as psychopathology. phenomena regarded as unique to man. Discussing the question of the phylogenetic precursors of psychiatric illness. thus, requires that one first examine the place of social and cognitive behaviors (alterations of which are covered by my definition of psychiatric illness) in a general biologic frame of reference. It is now held that at different points in the evolutionary time scale, prevailing social conditions served as factors that helped select for neurologic structures and changes: behavioral adaptations made possible by these changes had the effect of modifying the social conditions of man. thereby yeilding a new context for natural selection.18-20 All of this implies a connectedness between social conditions and neurobiologic traits. This connection between social and neurobiologic factors in the evolutionary process is held to account for possible similarities in the social and cognitive behaviors of man and other primates and also why the precise origins and meanings of culture are problematic. A consequence of this is that higher cerebral functions of man must be continuous with those of humanoid groups and might be with those found in man’s closest relatives, the apes.‘)‘-“” The guiding questions of the comparative neuropsychologist would include some of the following:25 (1) What anatomical differences are noted between the brain of man and that of the higher primates, and are these differences sufficiently explained by taking into account general evolutionary trends’? The latter include body size differences, progressive brain/body ratio increases, and additional predicted ratio increases or “residuals.” (2) What are the behavioral cot-t-elates or consequences of these trends (usually termed encephalization quotients)? (3) What is the range of variation in social and cognitive behavior within and between graded series of primate species’? (4) Under carefully controlled circumstances, what are the cognitive behavior capacities of higher primates and how do these differ from those of man when analogous modes of evaluation are followed’? The latter caveat force5 the scientist to employ ;I

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testing procedure that does not easily lend itself to verbal coding since this obviously places nonhumans at a relative disadvantage. (5) What social and/or cognitive behavior differences are noted between apes and man when homologous brain areas are injured? This question is deceptively simple; establishing brain-area homologies is problematic regardless of whether gross structural, cytoarchitectural, or patterns of anatomic connections are used. Furthermore, establishing comparability of extent of injury in brains of the same (not to say different) species presents no less of a formidable problem. Comparative analyses of the anatomy of the brain of higher primates and of man points to an evolutionary trend producing a proportionate increase in brain size/body size ratio. Many of the unique gross anatomic properties of the brain of man can, thus, be “predicted” mathematically by taking into account his body size. The relative sizes of different sectors of the human brain can also be predicted by controlling for its overall size. While acknowledging that reorganization in and between cortical and subcortical structures has undoubtedly occurred, and that the importance of brain size does not imply mass action (because functionally important and specialized subareas of the brain show proportionate increases), the continuity between man and primates in brain/ body ratios has led many to the parsimonious explanation that brain size alone (selection for this basic trait) can serve to explain a great deal of the bases for man’s “higher“ behaviors. For a critical exposition of this theme, the reader is urged to turn to recent Iiterature.26-30 There seems to be consensus that with regard to sensory processes alone, especially audition and vision (including threshold, color, acuity, and movement) few differences exist between man and the higher primates. However, in the areas of stimulus classification, problem solving, and associative learning (areas of behavior acknowledged as being more evolved and complex), there exist differences among primates of a quantitative (and in some cases, qualitative) sort.31 As an example, some primate species are able to transfer information across sensory modalities.32-34 Similarly, although the data here seem less controlled and more informally derived, it seems that only the higher primates can remember selectively, can anticipate the consequence of their actions, and can show instances of insight, planning and foresight in the solution of problems in the process constructively applying information about their immediate environment.35 The apes have been shown to possess the capacity for a concept of self and self-recognition, a qualitative difference that (together with man) apparently sets them apart from other primates.36 The spatial memory of apes (their ability to remember the location of objects hidden in a spatial territory) is such that is has drawn emphasis to the importance of considering representational processes in any assessment of their memory and learning abi1ities.37 Such a representational ability may, thus, be independent (in an evolutionary sense) from verbal language abilities. It is when projecting actions into the more distant future or recalling long past “creative” efforts that their cognitive abilities show a clear discontinuity from those of man. Nonetheless, the existence of such cognitive behaviors among the higher primates, the obvious preadaptations for a form of language and communication, and indeed

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the stylistic attributes of their group behavior is what has led to the claim of their possessing “culture.” Primate behavioral differences, of course, are mangified when man is considered, but the unique advantages devolving from the use of human verbal language in intermodal associations and in rehearsal of simple and complex actions generally needs to be stressed. At the very least, the verbal language system includes a phonologic, syntactic, and semantic component and there is evidence that each has a more or less dissociable neural representation.“*-“” However, exactly how these mechanisms and neural organizations function during cognition and to what extent (and how) they account for differences in behavior between man and the higher primates is not known with any degree of specificity. In brief, linguistic capacities make difficult an appraisal of exact differences and similarities between man and the higher primates and such appraisals are obviously critical for a full biologic understanding of the psychiatric illnesses like schizophrenia. A clear cut neural-behavior difference between man and the higher primates appears to be the degree of cerebral lateralization in man; that is asymmetries in function between the left and right sides of the brain. Thus, as recently reported, few primate species show clear-cut preferences for the use of the same hand or differential behavioral deficits when segments of only one side of the brain are injuredF5 Indeed, although there are some excepti0ns.j’ the left and right hemispheres among nonhuman primates appear on the whole to be functionally similar. In man. then, unilateral cerebral lesions suffice to produce highly specific and differential behavior defects whereas in nonhuman primates bilateral lesions seem to be required. Among nonprimates. a normal rate and level of learning seems to require two interconnected hemispheres whereas man and apparently nonhuman primates can learn a particular ability with only one hemisphere even if the neural system responsible for the ability functions optimally with both hemispheres. The special language capacities of man are held by many to be the principal sources of and bases for cerebral asymmetries of function and brain organization. Language functioning also presents the best evidence of the operation of the principle of mass action in the human brain; despite the structural differentiation between left and right temporal areas, either hemisphere can subserve language capacities, both seem to be required for optimal language and cognitive development, and a deficiency of cerebral tissue in the corresponding areas during development (in either hemisphere) is associated with cognitive behavior deficits (in language and in other abilities) in adult life. The acquisition and mastery of language may have a priority in the development of adult neural organization and function and the capacity in question appears quite specific in its neuronal requirements.25”‘-46 Interestingly, there is evidence to suggest that the right posterior temporal lobe in man. besides subserving spatial orientation, seems to be uniquely involved in the recognition of faces and, in this regard. this capacity is also specific in its neuronal requirements.“’ Lateralization of function of this degree is not at present known to be a feature of the brains ot other higher primates though instances of functional asymmetries have been

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reported. 25A1Development of the cognitive capacity of apes to somehow remove themselves from the here and now (to plan, look ahead, and use previous experience as a basis for action) is felt to be associated with the trend towards lateralization of cerebral functions, the full realization of which involves the special verbal and visual spatial abilities of man.4*Ag In summary, similarities and differences in brain-behavior relations among higher primates (including man) provide the context for an examination of the question of phylogenesis of a psychiatric illness like schizophrenia. Thus, if the primates including man are shown to have identical sensory thresholds to X modality of stimulation, to show identical functional effects when homologous brain areas Y are injured, or demonstrate similar behavioral stereotypes when toxic amounts of pharmacologic agent Z are administered, then the neurologic substrates responsible reflect uniformities wrought from the process of evolution of higher primates. If it can be demonstrated that psychiatric illnesses are outcomes of changes in such substrates, then one can claim that illnesses resembling them are logically possible occurrences in nonhuman groupings (see below). A problem for analysis becomes that of establishing their rate of occurrence in natural communities of nonhuman primates and clarifying their causation. Conversely, if man clearly differs from the rest of the primates and especially from the apes in behavioral property M, then the neurologic substrate responsible cannot as easily be shown to have a phylogenetic precursor. If this substrate is integral to the genesis of psychiatric illnesses, then the question of the prevalence of these illnesses in nonhumans becomes less tenable. It is very clear that verbal language and symbolic traits related to this have been and continue to be all important in the way brain function is realized in the human species. Whether these traits constitute qualitative or quantitative differences vis a vis higher primates is contested. The exact differences between man and nonhuman primates obviously determines how one orients to the problem of the general prevalence of psychiatric illness. A basic question is the following: are disturbances in language and related “symbolic” behavior criteria1 of psychiatric illness? Or does language merely render symbolically explicit and “public” what in effect are disturbances in neurological substrates mediating a range of other social, cognitive and motor behaviors? ON THE GENERAL PREVALENCE OF PSYCHIATRIC ILLNESSES An assumption that is implicit in this discussion is that a psychiatric illness such as schizophrenia implicates chemical and physiologic (disease) processes that are hereditable in certain members of the human species. Like other conditions that are considered disease entities in Western societies, then, many of the psychiatric ones display a frequency distribution, the structure of which can be related to “genetic factors.” An obvious research task is to clarify the genetic mechanisms and explicate how they are affected by environmental factors. In attempting to accomplish this, however, the psychiatric researcher encounters problems considerably different from those of other medical disciplines. Some of these problems will be discussed presently. A prevailing trend in clinical psychiatry is to view shizophrenia as a disorder of perception and cognition with the affected individual showing problems in

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the use of social symbols in the implementation of purposeful behavior.50 Such a formulation implies that it is a human disorder par excellence. In light of the previous discussion, however, one is compelled to ask whether schizophrenia is confined to man and whether social-cognitive behaviors are in fact central to “schizophrenia.” As indicated earlier, developments in ethology are quickly eroding comfort derived from the belief that there is a clear discontinuity between man and the higher primates regarding social-cognitive behavior. If nonhuman primates show behaviors that suggest the capacity for and apparent use of symbols as well as the existence of representational processes and even a concept of self, then the existence among them of social-cognitive disturbances analogous to schizophrenia are legitimate possibilities. Laboratory controlled social influences and/or the administration of neuro-pharmacologic agents can induce motor behavior anomalies (stereotypes) in nonhuman primates that have been jduged as similar to schizophrenia though whether attentional deficits are also found is not altogether clear. 51-55This indicates that such animals have the potential to develop this “condition.” That one could produce a neuropsychiatric entity like schizophrenia in a nonhuman organism does not, of course, answer the question of the biologic significance of this entity since it is the possibility of naturally occurring schizophrenia and its epidemiology in primate groups that is critical.56*“’ There is little information in primatology that deals with the accepted animal analogue of schizophrenia, namely motor stereotypes. 5R*59The information available does not include the rate of occurrence or long-range consequences of the syndrome. It is reasonable to argue that schizophrenia-like disturbances do in fact exist among nonhuman primates, but that their low visibility under field conditions is an outcome of two related factors. One is the tendency to look fat the human version of schizophrenia. which from a general biologic perspective. may indeed be atypical: that is, conditioned by factors peculiar to human groups and, hence, unlikely among nonhumans. Secondly, if human (symbolic) versions of schizophrenia exist in nonhuman groups. then one intuitively expects their prevalence to be low. As we will indicate. the strangeness and bizarreness of “human schizophrenia behavior” (its very asociality) makes participation in group and bonding activities difficult if not impossible. Affected members are, thus, easy victims of predation and other selective influences. One could hold that the social-cognitive changes seen in schizophrenia are magnified to us because of the important role that language and abstract thought play in human groupings. Perhaps it is disturbances in the morphology and temporal organization of certain motor behaviors that is distinctive of schizophrenia, viewed phylogenetically, with social-cognitive changes salient in human groups merely because of the importance of human language and social symbols. This line of reasoning implies that if one wishes to understand schizophrenia in a general biologic frame of reference. one must first conduct an analysis of the differences between categories of behavior and the role that Given this, one must specify each plays in adaptation and maladaptation. boundaries within which adaptation-maladaptation will be measured and also within which schizophrenia will be evaluated. It is clear that all of this requires clarifying the special roles played by verbal language in cognition and adapta-

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tion in human groups and also the adaptive consequences of motor behavior anomalies in nonhuman groups. In an obvious sense, then, searching fat phylogenetic precursors of psychiatric illness requires a disavowal of the a priori distinctiveness of human behaviors; that is that one employ a general biologic perspective within which human, humanoid, and infrahuman adaptation and maladaptation (i.e., illness) can be examined. ON THE PERSISTENCE OF ILLNESS IN INFRAHUMAN PRIMATES A large body of evidence in ethology suggests that diseased comembers are little tolerated and in fact treated harshly by comembers. There are indications that infrahuman primates have a striking and persistent neophobia and to the extent that a state of disease generates new and aberrant behaviors in a familiar they may be handled as aversive stimuli. There is very little evidence that the social group accords special favors or caregiving to defective or ill members. and once they become so debilitated that they no longer can carry their load in terms of obtaining food, protecting the social group, and staying with it during foraging, they are left behind to die. There are some widely accepted exceptions to this general rule: infants under the care of their mother may be tolerated even though they are unhealthy, ill or wounded familiars may be tolerated as long as they keep up with the group’s movements and compete for available food supplies, and elderly members of the group seem to be accepted even though they may not be as vigorous as they once were. Even in those laboratory situations where animals have been required to cooperate with each other in order to obtain food supplies. the performance of altruistic behavior (though in this case it is ultimately selfish: I’ll feed you, if you’ll feed me) is virtuahy impossible to demonstrate.6°-62 On the contrary, illness or wounding of a dominant male within a troop of monkeys seems to be associated with increased harrassment and vulnerability to displacement by his healthy competitors. Perhaps the most striking example of the lack of altruism is the killing of the harem male and the subsequent infanticide of all of his offspring in the langur. 63 There have been a number of studies in which brainoperated or drug-treated monkeys have been released into their own groups in the field.64-67 The treated monkeys were banished from the troop summarily (and in some cases were later found dead) while sham-operated subjects were permitted to rejoin the group. Studies with phencyclidine and chlorpromazine and THC have revealed that even very familiar social partners were treated harshly by their undrugged peers when they were behaving abnormally and similar findings have been published re: alcohol and amphetamine.68-71 The material presented above reinforces the point made earlier, namely that the concept disease applies nicely to infrahuman primates (and to living organisms generally), but that the concept illness-which suggests dependence, helpseeking, and reciprocated care-giving, and nurturance-does not. In any event, there seems little reason for expecting illnesses to persist in infrahuman primates and to have a high prevalence. The differences in the prevalence of illness in human vs infrahuman primates is highlighted when one considers psychiatric illnesses such as schizophrenia. In this instance, one notes behaviors very different from those of other

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(nonpsychiatric) illnesses. We are referring to the aggression, self-destruction, bizarre modes of interaction, social withdrawl, and alienation from comembers that are often seen in schizophrenia. The social implications of these latter behaviors seem contrary to biologic notions of bonding and group solidarity. Hallmarks of the behaviors that typically fall under the rubric of illness in human groups. which account for their persistence. and that conceivably might play analogous roles in infrahuman groups. are that the behaviors reflect dependence. need, and helplessness. It is this that elicits cooperation and nurturance. tendencies intrinsic to sociality. Behaviors thought of as psychotic may reflect need and dependence, but overtly often signal altogether opposite social tendencies and moreover can elicit aggression and neglect. The Hal-low studies have shown that monkeys subjected to rearing conditions that prevent their establishing normal social behaviors during infancy may lead to permanent isolation from social interactions with their conspecifics. Similarly. the precocial fowl that are imprinted on human caretakers and, thus. do not attach to their own species, do not behave socially in appropriate ways when they are adults.‘” Animals do not seem to go out of their way to accommodate to individuals of the same species who behave in unusual or abnormal ways-in fact. they seem to go out of their way to avoid such individuals (this is sometimes so for humans. but not invariably so-see below). One might speculate that behavioral anomalies are even less viable than physical ones in that the macaca with a broken limb might be able to hobble along with the group and still perform the appropriate social expressions to hang onto a social position while the bizarrely behaving member would be driven away even though he was physically healthy. Although there are a large number of observations and anecdotal reports that in nonliterate communities psychiatric-like behaviors are not tolerated, there is good evidence (and a wealth of observations and anecdotal reports) that in many instances individuals who display them are tolerated. helped, and protected.i4 In a word, they are viewed as ill and handled as such. A reading of the history of medicine discloses a similar uncertainty and/or ambivalence about what such behaviors signify and how they are to be handled. The variability in the way psychoticism is and has been handled in human communities could be judged to stem from its unbiologic aspects, but that human groups will handle this as illness seems on balance to be true. Thus, the concept of illness seems to apply to human psychotic behaviors such as those of schizophrenia and this stands in contrast to what one would intuitively posit to exist for psychotic behaviors among nonhuman gruops. In summary, psychiatric illnesses in human groups seem to be handled as are other illnesses. and this accounts for their prevalence and persistence. Given the nature of some of the behaviors of psychiatric illnesses, one would not expect these illnesses to persist or to be widely prevalent in infrahuman primates even if it could be shown that under natur-al field conditions they could develop. SUMMARY AND

view in psychiatry is that psychiatric illnesses, such as schizoreflect in their form and rationale aberrations of the special human

A traditional

phrenia,

CONCLUSIONS

286

HORACIO

FABREGA,

JR.

capacity for language, culture, and symbolization generally. An implicit tenet is that these human capacities, alone, serve to make understandable the general significance of psychiatric illnesses. In this paper, we have chosen to view these illnesses in a broader biologic framework. We have drawn attention to possible analogues of schizophrenia in infrahuman primates and suggested possible anthropocentric biases that may hinder our search for them. It would seem that depending on how one defines schizophrenia, its existence in infrahuman primates is a logical and empirical possibility, but that its prevalence is likely to be low given the way illness is dealt with in these groups. The special human capacity for symbols appears necessary for the idea of illness, vulnerability, finitude, and death to arise which, together with other human social abilities, give rise to ideas of religion, sanctity, and ethics all of which in modulating natural selection allow for the persistence of illness in genera1 and for psychiatric illness in particular. Implicit in this reasoning is the drawing of a clear distinction between the processes of biologic as opposed to cultural evolution. In the former, the concept of disease has currency since at stake is the selection for basic biologic traits that are realized in genes, chemistries, and physiologies. On the other hand, in the complementary process of cultural evolution, one is dealing with the selective retention of key symbols and correlated social institutions which prove advantageous to the individual (and by extension, the group) and in this context, the concept of illness including psychiatric illness may play an appropriate role. One could also argue that symbols and associated social and cognitive behavior capacities peculiar to man may provide special conditions for some of the precipitating causes of psychiatric illnesses. In other words, it may be that only through symbols can higher biologic forms achieve under natural field conditions the degree of isolation, distrust, and separation that contribute to the development of social and cognitive behavior anomalies such as schizophrenia (i.e., an argument for symbolic lesions). ACKNOWLEDGMENT I wish to express my appreciation to Robert E. Miller, Ph.D., who read earlier versions of this paper and helped me clarify some of the ideas in it.

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