Evolutionary Biology and Psychiatry: A Review Article, Study notes of Evolutionary biology

Download Evolutionary Biology and Psychiatry: A Review Article and more Study notes Evolutionary biology in PDF only on Docsity! Review article Evolutionary biology: a basic science for psychiatry? McGuire MT, Marks I, Nesse RM, Troisi A. Evolutionary biology: a basic science for psychiatry? Acta Psychiatr Scand 1992: 86: 89-96. Evolutionary biology has much to offer psychiatry. It distinguishes between ultimate and proximate explanations of behavior and addresses the functional significance of behavior. Subtheories, frequently voiced misconceptions, specific applications, testable hypotheses and limitations of evolutionary theory are reviewed. An evolutionary perspective is likely to improve understanding of psychopathology, refocus some clinical research, influence treatment and help integrate seemingly unrelated findings and theoretical explanations. Introduction Recent advances in evolutionary biology have im- plications for psychiatric theory, research and clin- ical practice. Evolutionary theory introduces a broad and much needed deductive framework; it facilitates the functional analysis of behavior; it identifies im- portant differences between ultimate causes and proximate mechanisms; it promotes a reassessment of current views about etiology and pathogenesis; and it alters treatment strategies and options. Evo- lutionists acknowledge that much human behavior is a product of personal and cultural experience, but argue that mind and culture themselves are products of evolution and are better understood when ana- lyzed within the evolutionary framework. Our assessment of the contributions that an evo- lutionary point of view can make to psychiatry be- gins with an analysis of its theoretical contributions followed by a discussion of common misconcep- tions. Possible applications to psychiatry are then evaluated. Finally, the limitations of the theory are reviewed. Only selected parts of evolutionary theory are dis- cussed. More comprehensive discussion of the the- M . T. McGuire’, I, Marks’, R. M. Nesse3, A. Troisi4 ’ Department of Psychiatry-Biobehavioral Sciences, School of Medicine, University of California at Los Angeles, USA, Institute of Psychiatry, DeCrispigny Park, London, United Kingdom, Department of Psychiatry, School of Medicine, University of Michigan, Ann Arbor, Michigan, USA, Clinica Psychiatrica, Universita di Roma, Italy Key words: evolutionary biology: psfchiatric theory; psychiatric research Michael T. McGuire, Department of Psychiatry-Biobehavioral Sciences, School of Medicine, University of California at Los Angeles, 760 Westwood Plaza, Los Angeles, CA 90024, USA Accepted for publication February 29, 1992 ory can be found in Williams (l), Wilson (2) and Alexander (3). Overview of the evolutionary approach to psychiatry Behavior Consider behaviors such as acquiring a mate, sexual intercourse, having offspring, parent-offspring bond- ing, stranger anxiety, infant and juvenile play, sibling rivalry, competition over resources, preferential in- vestment of resources in kin, reciprocal exchanges among nonkin, competition for social status, recog- nition and rejection of cheaters, deception of others and self-deception. Natural selection has shaped predispositions (strong biases) to engage in such be- haviors. Predispositions range from strong (such as withdrawal from a painful stimulus) to weak (such as preference for particular styles of music). The strengths of predispositions vary across indi- viduals. Experience and learning, which is also an evolved capacity, modify predispositions. Environ- mental options and constraints interact with evolved and prioritized behavior strategies to affect the prob- ability of immediate and long-term behavior. Psy- chological mechanisms (such as cognitive and psy- 89 McGuire et al. chodynamic ones) filter, modify, organize and focus information that influences behavior. Behaviors to which most persons are not predisposed (such as playing the piano) can be mastered, but usually after considerable effort. Nonetheless, the general behav- ior profiles and patterns of human behavior are set by the species’ genome and, within limits, unfold in predictable ways. The above and other behaviors are of special in- terest to psychiatry for several reasons: 1) mental disorders are associated with detectable abnormal- ities in the expression of such behaviors, such as reduced frequency of reciprocation (4-6); 2) an ad- equate understanding of some mental disorders (such as phobias, depression and somatoform disorders) requires an appreciation of the functional signifi- cance of such behaviors and of the evolved mecha- nisms that regulate them (7, 8); and 3) treatment strategies may change (for example greater empha- sis on functional outcomes and increased attention to environmental variables) with increasing appre- ciation of the evolutionary perspective. Natural selection favors brain mechanisms that result in behaviors conferring a reproductive advan- tage. Generally, such behaviors are neither atypical nor pathological. With few exceptions, however, mental disorders are atypical, pathological and mal- adaptive. Evolutionary theory provides a framework for analyzing adaptive behavior, the mechanisms that regulate it and the circumstances interfering with its normal expression (9). Psychopathology can be illuminated by insights into its normal adaptive pre- cursors. Most phobias, for example, are exaggerated normal fears (10, 11); minor adaptive rituals such as perfectionism are precursors for obsessive-com- pulsive disorder (10); normal mood swings can be viewed as precursors for manic-depressive illness (12); and normal sadness and social withdrawal may be precursors to clinical depression (13-15). Subt heories Since the early 1960s, a number of testable subthe- ories have been developed to explain specific behav- iors. Examples include: inclusive fitness or kin se- lection, reciprocal altruism, parent-offspring conflict, and cognitive/feeling mechanisms. Inclusive fitness. Preferential investment in kin is prominent in humans, as it is in other species. The tendency is to invest more in close than in distant kin, and for parents to invest more in offspring than vice versa. Hamilton (16) postulated that certain kin-related behavior is selected because it favors in- dividuals who share genes. A behavior costly to the self may nevertheless evolve if it increases the sur- vival and reproduction of kin who share the genes responsible for that predisposition. Kin-selection theory explains how altruistic behavior among kin facilitates the replication of genes shared by kin. The theory predicts, for example: that parents will invest more in their orspring than vice versa; that such investment is greater with higher parental assess- ment of the offspring’s reproductive potential; and that stepchildren are more likely to be abused that biological offspring. These predictions are well sup- ported by evidence (17-19). Reciprocal altruism. Although kin selection explains investment in kin, unrelated individuals also help each other (20). Such reciprocity exchanges are not confined to humans. Vampire bats, for example, share their blood meals after returning to their roost at dawn (21). Such exchanges even occur between species (22); alarm calls by one species alert mem- bers of other species, and cleaner fish remove par- asites from inside the mouths and gills of larger fish who protect cleaners from predation (23). Reciprocal altruism theory predicts: 1) A will help B (nonkin) if, in A’s view, the probability of recip- rocation by B times the probable benefit of this re- ciprocation equals or exceeds the initial cost to A (reciprocal behavior is distinguished for mutualism, where both parties gain simultaneously); 2) failure to reciprocate evokes moralistic aggression; 3) nonre- ciprocation will rise at the end of a period of asso- ciation (24); and 4) nonreciprocators will have fewer allies. These predictions are also supported by avail- able evidence (25,26). Evolutionary theory also explains why such emo- tions as pride, happiness, guilt and moralistic anger and such behaviors as guilt induction, intimidation and social ostracism have evolved. They facilitate reciprocal relationships (20, 25, 27, 28). Much of development and learning deals with refining recip- rocal behaviors, such as how to successfully manage reciprocity exchanges without being exploited or re- jected - battles among children often focus on who owes what to whom (29). Deviations from expected patterns of early kin and non-kin social relationships may contribute to disordered reciprocity relation- ships later in life (30). Parent-ofspring conyict and sibling rivilary. Although cooperation between parents, offspring and siblings is promoted by the genes they share in common, conflicts can be explained by the fact that many of their genes are not shared (31). Parental fitness (the number .of parental genes replicated among off- spring) is enhanced by the reduction of investment in maturing offspring in order to sooner reproduce again. Existing offspring try to counter this reduction and maximize their own fitness by delaying the birth of new siblings and by extracting as much from par- 90 Evolutionary psychobiology ousy should be more extreme in males than in fe- males. Essock-Wale & McGuire (18) confirm that, within kin networks, resources flow from older to younger persons. Buss (54, 5 5 ) has shown that the frequency of divorce increases in infertile marriages. There is mounting evidence for the prepotency and preparedness of fear (lo). Scenarios of past evolu- tionary events cannot be proven, but the number of possible scenarios can be limited, because given sce- narios predict certain outcomes, some of which can be tested. For example, the hypothesis that domain- specific cognitive and feeling mechanisms mediate reciprocal exchange implies that basic exchange rules will be comparable across cultures, and that precur- sors will be present in our close phylogenetic rela- tives (35). Natural selection should eliminate genes for mental disorders If most mental disorders are maladaptive, then why do they persist? Evolutionists have advanced several explanations for the persistence of mental disorders. First, atypical or deviant traits tend only to reduce, not eliminate, the number of offspring. Thus, once a disorder appears in a population, it may remain for a considerable time. Reduced reproductive suc- cess is seen in obsessive-compulsive disorder, for example, but success is only marginally lower than among normals (10). Second, many disorders (such as late-onset depression, Huntington’s disease and Alzheimer’s disease) mostly appear after peak re- production periods, so that inclusive fitness is less affected. A third possibility is heterosis, in which even if it is maladaptive to have the entire set of genes that is needed to produce a given disorder, having some of them (short of the number necessary for the full disorder) may be advantageous in certain environ- ments. Possessing all the genes for sickle cell anemia (homozygous state) leads to an early death, but car- rying only some of them (heterozygous state) en- hances resistance to malaria. Manic-depressive psy- chosis and obsessive-compulsive disorder are maladaptive, but cyclothymic and meticulous per- sonalities may provide an adaptive advantage in cer- tain environments. (A variation of this idea has been suggested for the persistence of senescence (44, 56): the very genes that lead to senility in old age may be those that confer some benefit in youth.) Fourth, recessive traits may be hard for natural selection to eliminate if they only partially compro- mise adaptation, and many forms of mental illness are so infrequent that selection may be slow. Finally, some behaviors that are disorders in one culture might not be disorders in other cultures. Dyslexia, some forms of antisocial behavior and certain un- stable personality variants are examples. Existing theories in other disciplines explain findings at least as well as evolutionary theory Evolutionists accept this view for certain features of current theories. Evolutionary theory does not re- place other psychiatric theories. Rather, it 1) offers an additional perspective, 2) helps explain hereto- fore overlooked and understudied features of disor- ders and 3) provides an integrating framework. By adding ultimate causation to the current focus on proximate factors (such as genes, physiology, learn- ing and psychodynamics), the theory identifies bi- ases and constraints of behavior and physiological systems. Proximate psychiatric theories explain many of the mechanisms of disorders, such as the biochemical explanations of depression, reduced se- rotonin turnover among chronic abusive criminals (57) and petty criminality as the substrates on which evolution acts (58-60). Evolution can help to ex- plain why these mechanisms exist at all. The degree to which psychiatry is likely to incor- porate an evolutionary perspective will depend on specific applications that inform our understanding and improve treatment. We now turn to the subject of applications. Applications Criteria for distinguishing normal from abnormal behavior The current criteria for defining mental disorders include: 1) association with a somatic lesion (ana- tomical to molecular); 2) statistical deviances from normality (such as excessive self-centeredness, learn- ing disabilities and bipolar illness); and 3) subjective distress. Some authors have suggested “biological disadvantage” as a more appropriate criterion for identifying mental disorders (61, 62). This view ac- cords with an evolutionary approach. A disorder must impose some form of fitness disadvantage. Sta- tistical deviance does not directly equate with dis- orders - mental retardation is a disorder but genius is not. Moreover, it is difficult to know whether a condition is pathological without considering the en- vironment in which it occurs. Depression may be adaptive in a supportive social environment, just as schizoid personality may be adaptive in isolated areas. Insofar as our present-day environment dif- fers from past environments in which current traits were adaptive, past adaptive behaviors may become maladaptive (such as the prepotency of animal fears being more fitting for our ancestors). Subjective suf- fering has a high probability of association with mal- adaptive situations, whether caused by external cir- cumstances or by brain disorders. Feelings of pleasure and pain probably evolved to tell us whether prevailing circumstances are adaptive (27). Yet, even emotional suffering may be useful, just as pain, nau- 93 McGuire et al. sea and fatigue are useful, although all indicate the presence of some danger. The preceding points imply that both the features of disorders and the disorders themselves should be evaluated in the context of evolution. Further, fea- tures of disorders may be adaptive or result as a consequence of ultimate causation. These possibili- ties result in alternative etiological explanations of disorders, raise questions about classification and imply different approaches to treatment. Pathogenesis Evolutionary theory focuses attention on distinctions between etiology (cause) from pathogenesis (mech- anism). Showing that depression is associated with alterations in norepinephrine or serotonin neuro- transmission (mechanism) does not reveal its cause (etiology). Biochemical alteration may be a common end product reflecting an environmental or genetic etiology, or both. Serotonin neurotransmission is al- tered by changes in social status, and testosterone and cortisol levels rise in response to a variety of social events (25,63). Such changes, in turn, alter the probability of behavior (such as responsiveness to others and vigilance), how information is pro- cessed and response to drugs (64). Certain social interactions are as essential for physiological and psychological homeostasis among adults as they are among infants. Persons vulnerable to mental disor- ders tend to have reduced capacities to manage their social environments to produce homeostasis and a greater probability of developing a disorder (45). Such evolutionary-oriented studies focus on behavior-physiology interactions and provide data for the empirical foundation of a more comprehen- sive model of mental disorders (65). Evolved psychological mechanisms As mentioned, natural selection is likely to have fa- vored the development of cognitive/feeling mecha- nisms preadapted to particular situations. Examples include: respond immediately to perceived external danger; avoid or retaliate against those who inflict pain; assess others’ ability to reciprocate helping; detect cheaters; and be vigilant towards actual and potential competitors. The characterization of such mechanisms is likely to be a major focus of research during the next decade. This research should lead to a description of mental disorders in terms such as underactive and overactive mechanisms (for exam- ple, over-reading or under-reading environmental dangers) as well as in the specification of such re- sponses to behavior, physiological states and func- tional consequences: for example, chronic anxiety results from an overactive response to danger and/ or from the failure of mechanisms that inform one that a danger has passed. Conversely, we may come to recognize new disorders characterized by defects in capacities for anxiety, normal sadness and jeal- ousy. A clear implication is that appropriate treat- ment depends on both the mechanism involved and how it is awry (66). Functional capacities and disorder classification Functional deficits are considered in Axis V in DSM- 111-R, but they are accorded far less importance in the day-to-day practice than are Axes I and 11. The concept of function and functional deficits is not the province of evolutionary theory. However, evolu- tionary theory provides a conceptual framework in which to organize and interpret functions and, in an evolutionary-derived classification, an assessment of functional capacities would be a pivotal taxonomic category. Persons with high anxiety, moderate de- pression, self-deception, mild bipolar illness and, in some instances, schizophrenia, often function above average. The same is true for some people who have socially unattractive traits, such as extreme self- centeredness and extreme needs to dominate and control others. For some disorders, decreased func- tional capacity is the primary finding, as is the case with antisocial personality and malingering. Assessment of functioning may also help explain within-disorder variance among current classifica- tion categories. Generalized anxiety disorder with minimal functional consequences may be classified separately from generalized anxiety disorder with major functional consequences. A focus on func- tional capacities would also alter treatment strate- gies and choices. A number of drugs that effectively reduce symptom intensity also reduce functional ca- pacities (such as decreased motivation and ability to concentrate). Integrating current theories Advocates of one school of psychiatry frequently disregard findings developed by other schools. Bio- logical psychiatrists are seldom interested in the findings of psychoanalysts or social psychiatrists, and some behaviorists ignore physiological aspects of mental disorders. Can such parochialism be changed? Evolutionary theory can encompass the major conceptual frameworks of psychiatry, help integrate relevant findings, appraise new ones and introduce additional possible explanations. Biological psychi- atry focuses on genetic-physiological predispositions and proximate mechanisms contributing to disor- ders, social psychiatry on environmental contribu- tions, behavioral psychiatry on atypical behavior and 94 Evolutionary psychobiology psychoanalysis on thoughts and feelings. Each of these focuses may best explain certain abnormal features, although in differing degrees within and across disorders. The addition of ultimate causation (such as predispositions to behave in certain species- characteristic ways), functional assessment, the possible adaptive function of certain features of dis- orders, trait distribution and the physiological con- sequences of person-environment interactions en- riches the database of psychiatry and allows us to address what is intuitively obvious, the concept of multiple bases for disorders. Evolutionary theory also offers psychiatry a de- ductive framework and a set of testable hypotheses. For example: multiple family placements of young children during critical periods of development is predicted to lead to both suboptimal refinement or learning of basic social skills and to the expression of certain predisposed traits that otherwise might not be expressed; diminution of within-disorder adaptive traits because of drug treatment would be predicted to result in noncompliance with treatment recommendations; and relinquishment of behavior that is offensive to others will occur only if alterna- tive behaviors are associated with desired benefits. Limitations of evolutionary theory A number of questions and unresolved issues re- main. The limits of evolutionary explanations have not been fully explored, particularly where 2 or more tendencies conflict (su:h as reciprocate by helping another vs invest in kin). For some behaviors, evo- lutionary explanations may prove to be the most parsimonious: for example, excessive risk-taking, antisocial behavior and depression following loss. Nevertheless, proximate events (such as the critical physiological details of a drug overdose) associated with many disorders are best judged from existing theories. Second, there may be limits to the degree to which evolutionary theory can be applied to individuals. The current form of the theory derives largely from population genetics and behavioral ecology, which focus on the behavior of groups, not of individuals. Potential difficulties due to this history are illustrated by considering trait distribution: on the one hand, the concept informs our understanding of trait var- iance; on the other, there are limits to what can be inferred from a distribution curve to an individual. Similar limitations apply to all major etiological and pathogenic theories of psychiatry. Third, the weights assigned to and the timing of many experiences are not significantly informed by the theory. Although there is general agreement throughout psychiatry and among evolutionary bi- ologists on the critical importance of certain devel- opmental experiences in the shaping of individuals, the importance of specific events and the time-frames in which they optimally occur remains largely an empirical issue. Extreme upbringing conditions (such as the total social deprivation of infants) have clear developmental effects, as do instances of the absence of essential neurochemicals for normal development (such as Tay-Sacks disease) or chromosomal aber- rations (such as Down’s syndrome). However, much of our knowledge is based on atypical situations that do not themselves directly inform our understanding of the complex process of development, its timing, and the impact of conditions generally accepted as being within the normal range. Conclusion A strong case can be made for evolutionary biology deepening our perspective by clarifying the concepts and explanatory power of ultimate to proximate ex- planations and by offering psychiatry an integrating paradigm. The theory puts humans back into an ecological context and raises questions about the normal operation of adaptive mechanisms, particu- larly those elicited by unusual circumstances. Per- haps surprisingly, its understanding and recognition of variation results in a particularly humanistic ori- entation to people’s problems. Acknowledgement The authors wish to thank the late Robert J. Stoller for his helpful comments on an earlier draft. References 1. WILLIAMS GC. Adaption and natural selection. Princeton: Princeton University Press, 1966. 2. WILSON M, DALY M. Competitiveness, risk taking, and vi- olence: the young male syndrome. Ethol Sociobiol 1985: 6: 59-73. 3. ALEXANDER D. Darwinism and human affairs. Seattle: University of Washington Press, 1979. 4. MCGUIRE MT, FAIRBANKS LA, ed. Ethological psychiatry. New York: Grune & Stratton, 1977. 5. MCGUIRE MT, ESSOCK-VITALE SM. Psychiatric disorders in the context of evolutionary biology: a functional classifi- cation of behavior. J Nerv Ment Dis 1981: 169: 672-686. 6. MCGUIRE MT, ESSOCK-VITALE SM. Psychiatric disorders in the context of evolutionary biology. J Nerv Ment Dis 1982: 7. NESSE RM. An evolutionary perspective on psychiatry. Compr Psychiatry 1984: 25: 575-580. 8. NESSE RM, LLOYD AT. The evolution of psychodynamic mechanisms. In: BARKOW J, COSMIDES L, TOOBY J, ed. The adaptive mind: evolutionary psychology and the generation of culture. Oxford: Oxford University Press (in press). 9. FEIERMAN J, ed. The ethology of psychiatric populations. Ethol Sociobiol 1987: 8: 1s-163s. 10. MARKS IM. Fears, phobias, and rituals. Oxford: Oxford University Press, 1987. 11. NESSE RM. An evolutionary perspective on panic disorder an agoraphobia. Ethol Sociobiol 1987: 8: 73s-83s. 170: 9-20. 95