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Evolutionary Perspectives on Personality Psychology
Richard L. Michalski Hollins University
Todd K. Shackelford Florida Atlantic University
[in press, August 2006, in G. J. Boyle, G. Matthews, & D. H. Saklofske (Eds.), The Handbook of Personality Theory and testing. London: Sage Publications.]
Address correspondence to Richard L. Michalski at Department of Psychology, Hollins University, P.O. Box 9658, Roanoke, VA 24020. Electronic mail may be sent to rmichalski@hollins.edu.
Evolutionary Perspectives on Personality Psychology Introduction and Background In this chapter, we argue that the development, structure, and processes of human personality have been crafted over hundreds of thousands of generations by natural and sexual selection. We argue that there is no scientifically viable alternative framework for understanding the historical origins of human personality and that human personality is thus best conceptualized with the theoretical tools developed in the evolutionary sciences. Personality, from this perspective, represents a meta-category of the output of a suite of species-typical, relatively domain-specific, evolved psychological mechanisms designed in response to the social adaptive problems recurrently faced by our ancestors throughout human evolutionary history. This conceptualization of human personality provides for a novel and valuable reinterpretation of several areas of personality psychology including personality consistency, individual differences in personality, sex differences and similarities, and contextual determinants of personality. The reconceptualization of personality from an evolutionary perspective already has lead to novel predictions about personality, including the function of social information conveyed through standings on the Big Five personality dimensions and in topics such as social anxiety, jealousy, altruism, aggression, psychopathology, mate preferences, desire for sexual variety, and father presence versus father absence in the development of sexual strategies. We argue that the limitations of the application of evolutionary theory to personality science are surmountable and that, despite these limitations, large strides have been made in anchoring personality science to the biological sciences by evolutionary scientists. The ontogeny, structure, and processes of human personality and of human nature, more generally, have been crafted over hundreds of thousands of generations by natural and sexual selection. There is no scientifically viable alternative framework for understanding the historical origins of human personality. The meta-theory of evolution by natural and sexual selection (Darwin, 1859/1958; 1871) has been supported, at various theoretical levels, by thousands of investigations spanning the disciplines of, for example, biology, ecology, medicine, anthropology, psychology, and ethology (see, e.g., Barkow, Cosmides, & Tooby, 1992; Daly & Wilson, 1983; Krebs & Davies, 1987; Smith & Winterhalder, 1992;
Any comprehensive theory of personality should provide answers to the following questions: What is human nature? What underlies individual differences? Is personality age-graded? How many levels of personality should be considered? What supportive empirical evidence is there for the theory? Does the theory generate specific testable predictions, or is it based upon post-hoc explanation of findings? In what ways are the sexes predicted to be different? In what ways are the sexes predicted to be similar? What causes these similarities and differences? What follows is a presentation of a developing theory of personality which aspires to answer each of these questions. Darwinian Concepts and Evolutionary Products The observation that species change over time was known long before Charles Darwin’s (1859) book The Origin of Species. Archaeological evidence had revealed changes in morphology and had revealed structures of organisms that appeared well-suited to the ecological niche occupied by the members of that species. What was lacking before publication of The Origin of Species was a causal mechanism to explain how species change over time. The theory of natural selection filled a gap in the explanatory framework which allowed researchers to explain changes in species over time. Darwin proposed natural selection as a solution to explain how variation in morphological (including psychological) characteristics better enabled organisms to survive and reproduce. Individuals that did not have the same morphology would have been out-reproduced by those individuals in ancestral environments that did. Through this process, successful variants would have become more frequently represented among organisms of a species and organisms with the less successful variants would have become less frequently represented. The process of natural selection requires three key components. Darwin proposed that selection operates on characteristics of organisms that vary, that are heritable, and that are passed on to that organism’s offspring. Variation, selection, and retention of mechanisms are the bases of natural selection. Among humans, for example, we vary along a wide variety of dimensions. We vary in morphological characteristics such as height and weight and we vary along psychological dimensions such as sexual orientation, sexual desire, and personality dimensions such as Dominance, Extraversion, and Emotional
Stability. There are also a variety of characteristics along which humans do not vary. We do not vary, genetic mutations excluded, along characteristics such as number of fingers, the presence of belly buttons, and number of eyes. From Darwin’s perspective, it is only along those characteristics on which we vary that natural selection can operate. Once variation on a particular trait or feature exists, natural selection operates on those features best suited for survival in the environment. The operation of natural selection requires that those characteristics be heritable (although, at the time, Darwin was unaware of the mechanism by which characteristics of individuals could be passed to offspring). Individuals with characteristics that aided their survival and reproduction passed those characteristics to their offspring at greater frequency and those characteristics became overrepresented in members of the species over the course of evolutionary history. Darwin was puzzled by the characteristics of organisms that thwart survival and are costly, both impeding survival and that are developmentally costly to produce. Reconciliation between observations of characteristics that impeded survival through increased predation (for example) was accomplished by Darwin with a second evolutionary theory—sexual selection theory (Darwin, 1871). Darwin’s (1871) theory of sexual selection was constructed to explain traits that seemingly reduced an organism’s chances of survival by virtue of evolution by natural selection. A human male’s greater aggression compared to human females comes at the cost of developing bodies capable of engaging in such conflicts (e.g., larger size, greater caloric intake necessary to grow and maintain such a body, maintaining higher testosterone levels). Sexual selection was proposed to explain how such features could be selected for (or at least not selected against) in ancestral environments. Darwin’s theory suggests that those features of organisms that increase (a) the chances of being selected by the other sex for copulation or (b) success in competition with the same sex for sexual access to the other will be selected. These facets of sexual selection are called intersexual selection and intrasexual (epigamic) selection, respectively. For nearly a century after the publication of sexual selection theory, focus was placed on biological sex as the driving force behind sexual selection. Publication of Trivers’s (1972) parental investment theory forced evolutionary biologists and, later, evolutionary psychologists to reformulate the
are not constrained in similar fashion. Males can continue investing mating effort in other fertile females. A female’s reproductive success is limited by her ability to manufacture eggs and a male’s reproductive success is limited by his ability to fertilize eggs. Reproductive variance is therefore greater among males than among females. For every man capable of successfully impregnating multiple females, another man is shut out of the reproductive game. A feature of this theory reveals that there are trade-offs between mating effort and parenting effort that are magnified in comparative research between species with sexually-asymmetric parental investment. Among humans, for example, a host of sex differences are expected to exist (Symons, 1979) that reflect investment differences that parents recurrently made in their offspring. These sex differences are expected to have arisen by processes of sexual selection that operated as a consequence of the difference between the sexes in parental investment in ancestral environments. Parental investment theory predicts that human females will be the more discriminating sex. Research has found consistently that females are less willing to engage in sex, desire fewer sexual partners, require greater time to pass prior to consenting to sex, have higher standards for sex partners, and report being more upset over emotional aspects of a partner’s infidelity compared to sexual aspects of his infidelity (for a review see Buss & Schmitt, 1993). They also have, at all time ranges, lower mortality rates compared to males. Cross-culturally, men invest substantially less than do women in their offspring (Lamb, 2001). Even in cultures with relatively high paternal investment, maternal investment dwarfs the investments made by fathers. Parent investment theory generates expectations of many sex-differentiated psychological mechanisms. The investment asymmetry between the sexes sets the stage for the evolution of mechanisms to solve social dilemmas posed by other family members. Offspring, for example, would have been selected to not allow the expression of genes that signaled dissimilarity to a putative father. Fertilization, being internal to women, results in paternity uncertainty for men. If men have psychological mechanisms designed to detect dissimilarities (or similarities) between themselves and their putative offspring, then selection would operate to produce phenotypic anonymity in offspring. The simple fact is that if the sexes did not differ in their relative contributions to parenting then the platform for which
additional adaptive problems selected for other psychological mechanisms would not exist. Future research is necessary to understand the developmental trajectories of specific psychological mechanisms designed in response to the selection pressures hypothesized by parental investment theory. One avenue of sex-differentiated psychology not fully explored is the impact of early family experiences on later mating strategies. Research on attachment styles and mating strategies reveals that female mating strategies may be calibrated to anticipate certain mating environments later in life based on the availability of parents and expectations that others will invest earlier in life. This relationship does not hold as strongly for males. Future research is necessary to examine why some features of sexual psychology and behavior related to early childhood experiences are present for females (Belsky, Steinberg, and Draper, 1991) and others emerge only for males (Michalski & Shackelford, 2002). Michalski and Shackelford, for example, found that men’s desired sexual strategies later in life are related to their birth order. Similar relationships do not hold for women. Why might men’s mating strategy be calibrated by their birth order and women’s mating strategy be calibrated by the attachment they develop with their parents? To answer these questions it is necessary to understand the products of evolutionary processes. The filtering processes of natural and sexual selection result in three products: adaptations, by- products of adaptations, and random variation or noise. Adaptations are the primary products of natural and sexual selection and can be defined as a “reliably developing structure in the organism, which, because it meshes with the recurrent structure of the world, causes the solution to an adaptive problem” (Tooby & Cosmides, 1992, p. 104). Adaptive problems refer to recurrent features of ancestral environments that impeded successful survival or reproduction. Buss (2004) presents the example of a preference for sweet, highly caloric foods. In ancestral environments, when access to food was less reliable than it is today, selection favored adaptations in humans that functioned to increase immediate caloric content. The criteria utilized to identify adaptations are stringent (Williams, 1966). Adaptations must show features of special design, including efficiency, precision, and reliability. By-products of adaptations include features or effects that are not considered to be adaptations
survival and reproduction faced by our ancestors. Personality psychology, in contrast, has been concerned largely with the ways in which humans differ. The divide between these two fields is obvious and raises questions that evolutionary psychologists need to address. If natural and sexual selection operates to filter less successful variants, why are stable, heritable individual differences maintained? The first theoretical link between these two literatures and attempt to reconcile this issue was provided by Buss (1984), who outlined four criteria according to which important sources of evolutionarily informed individual differences can be identified. These include heritability, inclusive fitness, sexual selection, and assortative mating. Each of these four criteria can be used to bridge the theoretical gap between evolutionary psychology and personality psychology. Buss (1991) and Buss and Greiling (1999) propose that personality may not reflect evolutionary noise or represent by-products of other adaptations but may instead reflect the social landscape of adaptive strategies. Buss highlights that that there are at least four explanations for personality and individual differences in humans:
- Differences in personality are heritable alternative strategies
- Differences in personality are calibrations to fluctuating strategies throughout development
- Differences in personality are due to contextual differences and personality reflects those contexts
- Personality differences emerge through calibration to various thresholds in development Appreciating that personality differences between individuals may reflect social landscapes, it is reasonable to question whether personality has an impact on shaping sexual desire, motivation, and attraction. Personality can be used as a source of information that answers some of the most important social dilemmas that humans have evolved to solve. Evolutionary psychologists have argued, for example, that the Big-Five personality characteristics summarize the most important facets of social landscapes. Perceiving, attending to, and acting upon differences in others likely would have yielded important benefits in ancestral environments. For example, Openness/Intellect of others can be used as a criterion for seeking out advice. Conscientiousness may be evaluated to assess whom to trust to complete important tasks. Agreeableness may be evaluated as an index of an individual’s willingness to cooperate
and to conform to group norms by suspending their individual concerns. Neuroticism may signify the inability to negotiate tasks effectively. Extraversion or surgency may be assessed as an index of who is likely to rise in the local status hierarchy. From an evolutionary psychological perspective, human personality structure is comprised of a finite though numerous collection of species-typical, relatively domain-specific psychological mechanisms that have evolved over human evolutionary history because they solved the adaptive problems ancestral humans confronted. Personality is comprised of psychological mechanisms. Every theory of human personality—even the most environmentalistic—assumes that personality is at some basic level constructed of psychological mechanisms (Symons, 1987). If two members of a given species, or if two members of two different species are exposed to identical stimuli and respond in non- identical ways, we must infer the existence and operation of mechanisms internal to the organisms. These mechanisms can best be described as information-processing devices. These mechanisms take in certain classes of information, process that information according to a set of decision rules, and then generate output correlated with survival or reproductive success in ancestral environments. The information accepted for processing into the mechanism may come from other psychological mechanisms internal to the organism, or it may originate in the external environment—more often than not the particularly social environment comprised of other humans operating according to like mechanisms. The output generated by a psychological mechanism may be in the form of information which is channeled to and accepted by other psychological mechanisms internal to the organism. Or the output may be in the form of behavior, affect, or cognition enacted by the organism (Buss, 1991). The psychological mechanisms underlying personality have evolved over human evolutionary history because they solved the adaptive problems ancestral humans confronted. Certain problems have been recurrently faced by ancestral humans. Consider the problem of which foods to ingest. To survive, certain nutrients had to be ingested (and, conversely, various toxins had to be avoided). This is a complicated problem when considered at the level of basic decision processes. Ancestral humans had to distinguish nutritive from non-nutritive goods, poisonous from non-poisonous fruits, vegetables, and
expected because all modern humans are, by definition, the evolutionary descendents of those ancestral humans who successfully solved the various adaptive problems they confronted. If it is the case, then, that personality is comprised of a finite though numerous species-typical and domain-specific psychological mechanisms, does this mean that personality is stable or consistent from birth to death? Or might it be somehow dependent on the context or environment? Evolutionary psychological theories do not imply the existence of adaptations that are incapable of change or are forever bound by our genome (Bjorklund & Pellegrini, 2002; Buss, 2004; Tooby & Cosmides, 1992). Few evolutionary psychologists actively present hypotheses and theories that stress the role that the environment has in shaping the expression of evolved modules of the mind, but these theories are nonetheless not deterministic theories. An examination of the arguments surrounding the claim that evolutionary psychology is a theory of genetic determinism must start with an examination of what evolutionary psychologists actually propose. Tooby and Cosmides (1992) argue that developmental programs responsible for assembling an adaptation are also adaptations whose primary function is to reconstruct in offspring the design that enhanced reproduction in the preceding generation. They specifically note that it is useful to consider genes together with developmental programs as an integrated suite of adaptations. The reliable development of an organism’s phenotypic features (including personality and sexual strategies) does not imply that these features are not modifiable. Developmental adaptations do not assemble an organism of fixed design but rather a set of expressed adaptations according to variables such as age, sex, and circumstance-dependent design specifications. Adaptive problems are often specific to particular life stages. Organisms must have the necessary adaptations for the particular stage regardless of whether they appear before they are necessary or continue after they are necessary. Tooby and Cosmides argue that every feature of every phenotype is equally determined by the interaction of that organism’s genes and its ontogenetic environment. “Biology,” therefore, cannot be segregated to certain traits and not to others. In stressing the role of the environment, Tooby and Cosmides note that the “developmentally relevant environment” refers to those features of the world that are rendered developmentally relevant by the evolved design of an organism’s developmental adaptations.
The assumption that genes are, therefore, the only target of natural selection is a misconception. Genes and developmentally relevant environments (species-typical environments) are both products of the evolutionary process. By selecting a developmental adaptation, for example, the evolutionary process also is selecting the triggers that the mechanisms will use to build an adaptation. Functional design is revealed as much by genes as it is by the environment that those genes use to construct an adaptation. Evolution by natural and sexual selection is recognized as the origin of the many special-purpose and domain-specific cognitive decision-rules (psychological mechanisms) according to which humans function. However, and crucial to this perspective, evolutionary psychology holds as a central goal to determine the historical, developmental, and situational forms of contextual input processed by the psychological mechanisms that guide human behavior. Evolutionary psychologists are not “genetic determinists.” Rather, a key message of evolutionary psychology is that the complex architecture of species-typical, domain-specific psychological mechanisms allows for the impressive context-dependant flexibility of human behavior, cognition, and affect (Buss, 1991; DeKay & Buss, 1992). Modern evolutionary approaches aspire to understand—in addition to our species-typical, culturally differentiated, and sex-specific human nature—the ways that individuals differ within species, within cultures, and within sex. Thus, the architectural unit of personality is the evolved psychological mechanism. But these mechanisms cannot and do not operate in a vacuum. The mechanisms are dependant for their activation on the contextual input for which they have evolved sensitivity. Personality is, therefore, relatively stable in the sense of being basically comprised of a finite (though numerous) collection of species-typical psychological mechanisms. At the level of the cognitive, affective, and behavioral output of these mechanisms, however, personality is better described as variable. The most accurate depiction of personality is that it is both consistent and variable—that it is comprised of a finite set of species-typical and domain-specific psychological mechanisms that depend for their activation on relevant contextual input. And because no two individual psychologies will receive and process identical input in an identical manner, there is room enough for individual differences. At the same time, we can expect base level
A second evolutionary approach investigates the environment that is currently inhabited for an explanation of manifest individual differences. Thus, for example, Flinn (1988) finds that mate- guarding of Trinidadian females by males varies as a function of the reproductive status of the female: she is guarded against other males significantly more when she is fecund (impregnable) than when she is not fecund. A third evolutionary approach to individual differences examines “reactive individual differences.” The general thesis is that there are evolved mechanisms which take as input a circumscribed class of anatomical data. Based on the processing of such information, the mechanisms guide the organism to adopt one strategy over an alternative in a given domain of behavior. For example, individuals who are small in stature and without physical size and strength will likely be most successful pursuing a strategy of diplomacy (rather than, say, aggressivity) in interacting with conspecifics. A person with a large, muscular build, on the other hand, may be anatomically and physiologically “prepared” to pursue an aggressive strategy in interactions with others (DeKay & Buss, 1992; Tooby & Cosmides, 1990). A fourth evolutionary approach to explaining individual variation is exemplified by the work of Gangestad and Simpson (1990), who conceptualize the adoption of one of two general sexual strategies in terms of genetic differences arising through frequency-dependent selection. Gangestad and Simpson argue that individuals differ on the dimension of “sociosexuality.” Sociosexuality refers to an individual’s willingness to engage in sexual intercourse with little or no emotional investment in or commitment to the relationship. Gangestad and Simpson present evidence supporting the proposal that two alternative sexual strategies (high and low sociosexuality) have been selected for, with the result a bimodal distribution of these strategies in the current population. They suggest that the adoption of one of the strategies is heritable and that, moreover, a variety of personality characteristics covary with each strategy in a way that is consistent with evolutionary reasoning. It is important to recognize that each of these approaches to understanding individual differences is complementary, rather than competing or mutually exclusive. Each perspective offers a different
window through which to glimpse the structure of human personality. Application of each of these areas has profitably proceeded in the area of human sexual psychology. Personality and Sexual Psychology Examinations of the relationships between personality and sexuality began in earnest with Eysenck (1976). Following from the guidance offered from an evolutionary perspective, we can attempt to couch our understanding of the relationships between personality and sexual psychology as a function of sexual selection. Parental investment theory (Trivers, 1972) predicts that human males will devote more resources to mating effort and that human females will devote more resources to parental investment by virtue of asymmetries in assurances of parentage. It is, therefore, not surprising that we observe differences in pursuit of social status, sensation seeking, extraversion, and risk-taking favoring men and that we observe differences in love/nurturance favoring women (MacDonald, 1998). Linked with those characteristics that the sexes appear to differ on are characteristics that men and women view as desirable in a long-term partner. Surbey and Conohan (2000) found that female undergraduate students desired personality characteristics such as brightness, generosity, and having a sense of humor in a hypothetical partner with whom they would consider having sexual intercourse. Jensen-Campbell, Graziano, and West (1995) report that females prefer as mates males high on altruism and Agreeableness, with the highest ratings of attraction provided for agreeable and dominant males. Buss and Barnes (1986) report that women rank characteristics such as considerate, honest, dependable, kind, and understanding higher in a prospective mate than do men. Given that the obligatory parental investment costs are greater for women than for men, ancestral women with preferences that guided them towards prospective mates who were more likely to provision them and their offspring would have been at a selective advantage relative to those women in ancestral environments that were indifferent to the personality characteristics linked with status and resources in men (Buss, 2003). Research has revealed that personality plays a key role in human sexual psychology. Personality is a critical component of human mate choice (Buss, 2003) and is associated with the dissolution of relationships (Betzig, 1989). Figueredo, Sefcek, and Jones (2004), for example, report that men and
Although females have not faced the adaptive problem of uncertain parentage, the sexual infidelity of their mate likely served as a cue to the potential or current loss of other reproductively valuable and typically mateship-specific resources. That is, a woman may fear that the resources her mate contributes to their relationship (historically in the form of, for example, protection of her and their offspring from predation and hostile conspecifics; social and political support of her and their offspring; and basic provisionment of food, shelter, and related resources to her and their offspring) will be diverted to another woman and the other woman's offspring (Buss & Schmitt, 1993; Daly & Wilson, 1988). The ubiquitous phenomenon of female prostitution supports the observation—implied in the mated woman’s concern over the sexual infidelity of her mate—that men often barter reproductively valuable resources for sexual access to females (Daly & Wilson, 1988). Feelings of betrayal incited in a woman in response to the real or imagined sexual infidelity of her mate can thus be understood as a response to the threatened loss of reproductively valuable resources (Buss, et al., 1992; Buss & Schmitt, 1993). Similarly, extra-relationship romantic emotional involvement will incite intense feelings of betrayal in the context of a mateship. This is true for both males and females (Buss et al., 1992; Buss & Schmitt, 1993; Wiederman & Allgeier, 1993; Wilson & Daly, 1992). Accordingly, a woman may fear that the resources her mate contributes to their relationship will be diverted to another woman and the other woman’s offspring (Buss & Schmitt, 1993; Daly & Wilson, 1988). A man, on the other hand, may fear that the romantic emotional involvement of his mate with another male will escalate to sexual involvement, potentially rendering him a cuckold (see Buss, 2000, for a review of research). Both sexes are predicted to feel betrayed by the sexual or romantic emotional infidelity of their long-term mate. Indeed, research paradigms that do not definitively disassociate sexual from romantic mate infidelity (reviewed in Wiederman & Allgeier, 1993) find no significant quantitative sex differences in what are effectively global measures of incited betrayal or jealousy. However, and consistent with the logic of evolutionary psychology, when the disassociation of sexual from romantic infidelity is made, men display greater psychological, physiological, and behavioral distress to a mate’s sexual infidelity, whereas women display greater distress to a mate’s romantic emotional infidelity (Buss et al., 1992; Buss,
Shackelford, Kirkpatrick, Choe, Lim, Hasegawa, Hasegawa, & Bennett, 1999; Buunk, Angleitner, Oubaid, & Buss, 1996; DeSteno & Salovey, 1996; Geary, Rumsey, Bow-Thomas, & Hoard, 1995; Harris, 2000; Harris & Christenfeld, 1996; Shackelford, Buss, & Bennett, in press; Wiederman & Allgeier, 1993; Wiederman & Kendall, 1999; but see Harris, 2000, and Grice & Seely, 2000, for partial failures to replicate the sex difference using physiological measures). To reiterate, the pressing adaptive problem for mated men is the threat of cuckoldry—associated directly with a mate’s sexual infidelity. The pressing adaptive problem for mated females is the threatened loss of reproductively valuable time and resources contributed by her mate—associated with her mate’s romantic emotional involvement (and concomitant resource investment) in another woman and the other woman’s offspring. That is, for the mated woman, the adaptive problem is not the sexual infidelity of her mate per se ; rather, it is the threatened diversion of his time and resources to another woman in a bartering effort to gain (and perhaps retain) sexual access to her. Thus, assuming the two types of infidelity are disassociated, men will experience more intense feelings of betrayal in response to their mate's sexual infidelity. Women, on the other hand, will experience more intense feelings of betrayal in response to the romantic emotional infidelity of their mate. Evolution by natural and sexual selection is recognized as the origin of the many special-purpose and relatively domain-specific psychological mechanisms that comprise the structure of human personality. As noted earlier, however, these mechanisms are dependant for their activation on the appropriate contextual or environmental input. Only certain classes of information will be accepted and processed by a given psychological mechanism. Consider again the case of extra-relationship sexual involvement (see Shackelford & Buss, 1996). Evolutionary logic suggests that the betrayal felt by a mate's extra-relationship sexual involvement will be most intense when it occurs with an enemy/rival of the mate’s partner: Not only is exclusive sexual access (and perhaps various other forms of reproductively valuable resources) lost; in addition, it is lost to one’s competitor. Similarly devastating would be the case where one’s mate engages sexual relations with one’s close same-sex friend. Again, exclusive sexual access (and perhaps other forms of reproductively valuable resources) is lost; in addition, a close reciprocal alliance is disrupted in
