I would submit that these personality factors are not scientifically valid, but socially invented and constructed; not objective, but subjective. This “theory without proof” lies outside the scientific method of proof – but these “speculations” are the basis for Psychology; the socio-cultural Western religion.
Note the highly “socially judgmental” descriptions of “low scorers” and “high scorers”. A polarized view of human personality, in which “socially approved” characteristics (outgoing, empathetic, warm, helpful) are given “high scores” The trait categories are also skewed: extraversion, agreeableness, openness – conscientiousness, neuroticism! How do these highly subjective ideas drive the relentless push toward conformity to social prescriptions for “normal, typical, or idealized” behavior, which is determined by culture? What they “measure” is the opinion of the measurer – and his or her socio-cultural agenda. As the author points out, “However, it is important not to conﬂate social desirability with positive effects on ﬁtness.”
continued from: The Evolution of Personality Variation in Humans and animals by Daniel Nettle, Newcastle University in American Psychologist, 2006 Evolution and Behaviour Research Group, Division of Psychology, Henry Wellcome Building, University of Newcastle, Newcastle NE2 4HH, United Kingdom.
Human Personality Traits
The rest of this article follows the structure of the ﬁve factor model of personality (Costa & McCrae, 1985, 1992; Digman, 1990). Though the ﬁve broad factors, or domains, are decomposable into ﬁner facets (Costa & McCrae, 1985) and certainly do not capture all the variation in human personality (Paunonen & Jackson, 2000), there is broad consensus that they are useful representations of the major axes of variation in human disposition (Digman, 1990). Following the considerations outlined in the previous section, I brieﬂy examine the nature of each domain and consider the kinds of costs and beneﬁts that increasing the level of the domain might have with respect to biological ﬁtness. The reviews here are speculative, but they are offered in the hope of stimulating empirical work and of drawing psychologists’ attention to the idea that changing the level of a trait is associated with ﬁtness costs as well as ﬁtness beneﬁts.
Note that many of the “negative risk factors” are actually admired and rewarded in American males: I would go so far as to say, that ‘extraversion’ is tailor-made permission for “boys to be boys” as defined culturally. In females, these same behaviors are viewed negatively. Also, my comments refer to the BIG 5 model, not to the author’s concepts.
A dimension related to positive emotion, exploratory activity, and reward is a feature common to all personality frameworks and theories. Its most common label is extraversion, and its proximate basis is thought to involve variation in dopamine-mediated reward circuits in the brain (Depue & Collins, 1999). I have outlined a trade-offs-based evolutionary model for the maintenance of polymorphism in extraversion (Nettle, 2005). Extraversion is strongly and positively related to number of sexual partners (Heaven, Fitzpatrick, Craig, Kelly, & Sebar, 2000; Nettle, 2005), which, for men in particular, can increase ﬁtness. High scorers are also more likely to engage in extrapair copulations or to terminate a relationship for another. This may lead to their securing mates of higher quality than those secured by individuals who are more constant in their choice of partners. The beneﬁts of extraversion are not limited to mating, as extraverts, or those high on the closely correlated trait of sensation seeking, initiate more social behavior (Buchanan, Johnson, & Goldberg, 2005) and have more social support (Franken, Gibson, & Mohan, 1990) than others. Moreover, they are more physically active and undertake more exploration of their environment (Chen et al., 1999; Kircaldy, 1982). However, in pursuing high sexual diversity, and high levels of exploration and activity in general, extraverts also expose themselves to risk. Those who are hospitalized due to accident or illness are higher in extraversion than those who are not (Nettle, 2005), and those who suffer traumatic injury have been found to be high in sensation seeking (Field & O’Keefe, 2004). High extraversion or sensation seeking scorers also have elevated probabilities of migrating (Chen et al., 1999), becoming involved in criminal or antisocial behavior (Ellis, 1987), and being arrested (Samuels et al., 2004). All of these are sources of risk, risk that in the ancestral environment might have meant social ostracism or death. Moreover, because of their turnover of relationships, extraverts have an elevated probability of
exposing their offspring to step-parenting, which is a known risk factor for child well-being. One can thus conceive of extraversion as leading to beneﬁts in terms of mating opportunities and exploration of novel aspects of the environment but carrying costs in terms of personal survival and possibly offspring welfare. It is unlikely that there will be a universal optimal position on this trade-off curve. Instead, local conditions, including the density and behavioral strategies of surrounding individuals, could lead to a constant ﬂuctuation in the optimal value, and hence genetic polymorphism would be retained.
Neuroticism (Traditionally in psych / psych dogma, Neuroticism is by default the normal “female” condition.)
The neuroticism personality axis is associated with variation in the activity levels of negative emotion systems such as fear, sadness, anxiety, and guilt. The negative effects of neuroticism are well-known in the psychological literature. High neuroticism is a strong predictor of psychiatric disorder in general (Claridge & Davis, 2001), particularly depression and anxiety. Neuroticism is also associated with impaired physical health, presumably through chronic activation of stress mechanisms (Neeleman et al., 2002). Neuroticism is a predictor of relationship failure and social isolation (Kelly & Conley, 1987). A much more challenging issue, then, is ﬁnding any compensatory beneﬁt to neuroticism. However, given the normal distribution observed in the human population, and the persistence of lineages demonstrably high in the trait, such a beneﬁt seems likely. Studies in nonhuman animals, such as guppies (see the Evolution of Variation section), suggest that vigilance and wariness are both highly beneﬁcial in avoiding predation and highly costly because they are quickly lost when predation pressure is absent. In ancestral environments, a level of neuroticism may have been necessary for avoidance of acute dangers. Anxiety, of which neuroticism can be considered a trait measure, enhances detection of threatening stimuli by speeding up the reaction to them, interpreting ambiguous stimuli as negative, and locking attention onto them (Mathews, Mackintosh, & Fulcher, 1997).
Because actual physical threats are generally attenuated in contemporary situations, (this is highly dependent on gender, race, socio-economic and class status and geographical location) the safety beneﬁts of neuroticism may be hard to detect empirically. However, certain groups who take extreme risks, such as alpinists (mostly male?) (Goma-i-Freixanet, 1991) and Mount Everest climbers (Egan & Stelmack, 2003), have been found to be unusually low in neuroticism. Given the high mortality involved in such endeavors (around 300 people have died in attempting Everest), this ﬁnding suggests that neuroticism can be protective. There may also be other kinds of beneﬁts to neuroticism. Neuroticism is positively correlated with competitiveness (Ross, Stewart, Mugge, & Fultz, 2001). McKenzie has shown that, among university students, academic success is strongly positively correlated with neuroticism among those who are resilient enough to cope with its effects (McKenzie, 1989; McKenzie, Taghavi-Knosary, & Tindell, 2000). Thus negative affect can be channeled into striving to better one’s position. However, here neuroticism certainly interacts with other factors. When intelligence or conscientiousness is high, for example, the outcomes of neuroticism may be signiﬁcantly different than when such factors are low. Thus it is quite possible that very low neuroticism has ﬁtness disadvantages in terms of lack of striving or hazard avoidance. Although very high neuroticism has evident drawbacks, it may also serve as a motivator to achievement in competitive ﬁelds among those equipped to succeed. Thus the optimal value of neuroticism would plausibly depend on precise local conditions and other attributes of the person, leading to the maintenance of polymorphism.
The trait of openness to experience again seems, at ﬁrst blush, to be an unalloyed good. Openness is positively related to artistic creativity (McCrae, 1987). According to Miller’s (1999; 2000a) cultural courtship model, creative production in artistic domains serves to attract mates, and there is evidence that women ﬁnd creativity attractive, (Again, we have the problem of just who is defining and judging what qualifies as “creative production”, a highly subjective culturally-dependent matter, often attributed in the U.S. to whatever/whomever makes a profit…) creative especially during the most fertile phase of the menstrual cycle (Haselton & Miller, 2006), and that poets and visual artists have higher numbers of sexual partners than controls (Nettle & Clegg, 2006). The core of openness seems to be a divergent cognitive style that seeks novelty and complexity and makes associations or mappings between apparently disparate domains (McCrae, 1987). Though such a cognitive style might appear purely beneﬁcial, it is conceptually very similar to components of schizotypy, or proneness to psychosis (of course; creative types are “dangerous” in a rigid, impoverished culture of social conformity) (Green & Williams, 1999; Woody & Claridge, 1977). Indeed, ﬁve-factor Openness correlates positively with the Unusual Experiences scale of the Oxford–Liverpool Inventory for Feelings and Experiences schizotypy inventory (Mason, Claridge, & Jackson, 1995; Rawlings & Freeman, 1997). The Unusual Experiences scale is also correlated with measures of creativity (Nettle, in press-b; Schuldberg, 2000). Individuals scoring high in Unusual Experiences and on measures of creativity have increased levels of paranormal belief (McCreery & Claridge, 2002; Thalbourne, 2000; Thalbourne & Delin, 1994), and ﬁve-factor Openness itself is positively correlated with beliefs in the paranormal (Charlton, 2005). The Unusual Experiences trait is elevated in schizophrenia patients (Nettle, in press), and an extremely similar scale predicted the onset of schizophrenia in a longitudinal study (Chapman, Chapman, Kwapil, Eckblad,&Zinser,1994).Thus, openness and its covariates are associated with damaging psychotic and delusional phenomena as well as high function. Openness itself has been found to be associated with depression (Nowakowska, Strong, Santosa, Wang, & Ketter, 2005), as has a high score on the Unusual Experiences scale (Nettle, in press-b). Thus, the unusual thinking style characteristic of openness can lead to nonveridical ideas about the world, from supernatural or paranormal belief systems to the frank break with reality that is psychosis. What determines whether the outcome of openness is benign or pathological is not fully understood. It may be a simple matter of degree, or there may be interactions with developmental events. Poets, for example, differ from schizophrenia patients not in their Unusual Experiences scores, which are in the same range, but in the absence of negative symptoms such as anhedonia and social withdrawal (Nettle, in press-b).
And yet, we relentlessly promote creativity and “out of the box” thinking in American schools as social positives; are we actually promoting sexual promiscuity, schizophrenia, “Ancient Alien” “UFO” “Paranormal” delusion and psychotic behavior?
The Unusual Experiences trait is positively correlated with mating success in nonclinical populations, at least partly because it leads to creativity (Nettle & Clegg, 2006). However, when it leads to schizophrenia, reproductive success is much reduced (Avila et al., 2001; Bassett et al., 1996). Thus the ﬁtness payoffs to openness appear to be very context or condition dependent, leading to the retention of variation.
The remaining two personality domains, conscientiousness and agreeableness, are often thought of as being unalloyed in their beneﬁts, because they are generally negatively related to measures of delinquency and antisocial behavior (e.g. Heaven, 1996). However, it is important not to conﬂate social desirability with positive effects on ﬁtness. Natural selection favors traits that increase reproductive success, including many cases in which this success comes at the expense of other individuals. It is likely that ﬁtness can be enhanced by a capacity to demand a free ride, break rules, and cheat on others under certain circumstances. Conscientiousness involves orderliness and self-control in the pursuit of goals. A by-product of conscientiousness is that immediate gratiﬁcation is often delayed in favor of a longer term plan. This leads, for example, to a positive association of conscientiousness with life expectancy (Friedman et al., 1995), which works through adoption of healthy behaviors and avoidance of unhygienic risks. Very high levels of traits related to conscientiousness —moral principle, perfectionism, and self-control—are found in patients with eating disorders and with obsessive-compulsive personality disorder (Austin & Deary, 2000; Claridge & Davis, 2003).
Though some obsessional individuals can be very high achievers in the modern context, it is not evident that their ﬁtness would always have been maximal in a variable and unpredictable ancestral environment. Their extreme self control not only may be damaging, as their routines become pathological, but may lead to the missing of spontaneous opportunities to enhance reproductive success. Highly conscientious individuals have fewer short-term mating episodes (Schmidt, 2004) and will forgo opportunities to take an immediate return that may be to their advantage. Adaptations that orient the organism toward working for long-term payoffs will tend to have the effect of reducing the opportunistic taking of immediate ones. This can have ﬁtness costs and beneﬁts, which will vary with local conditions.
Agreeableness, with its correlates of empathy and trust, is also generally seen as beneﬁcial by personality psychologists, and its absence is associated with antisocial personality disorder (Austin & Deary, 2000). Agreeableness is strongly correlated with Baron-Cohen’s empathizing scale (Nettle, in press-a), which is in turn argued to measure theory of mind abilities and the awareness of others’ mental states (Baron-Cohen & Wheelwright, 2004). Several evolutionary psychologists have argued plausibly that as a highly social species, humans have been under strong selection to attend to and track the mental states of others (Byrne & Whiten, 1988; Dunbar, 1996; Humphrey, 1976). Others have noted that we seem to be unique among mammals in the extent of our cooperation with unrelated conspeciﬁcs. Inasmuch as agreeableness facilitates these interactions, it would be highly advantageous. Agreeable individuals have harmonious interpersonal interactions and avoid violence and interpersonal hostility (Caprara, Barbaranelli, & Zimbardo, 1996; Heaven, 1996; Suls, Martin, & David, 1998). They are much valued as friends and coalition partners. Although this may be true, a vast literature in theoretical biology has been devoted to demonstrating that unconditional trust of others is almost never an adaptive strategy. Across a wide variety of conditions, unconditional trusters are invariably outcompeted by defectors or by those whose trust is conditional or selective (see, e.g., Axelrod & Hamilton, 1981; Maynard-Smith, 1982; Trivers, 1971). Levels of aggression can often be selected for (Maynard-Smith, 1982). Very high agreeableness, if it led to an excessive attention to the needs and interests of others, or excessive trusting, would be detrimental to ﬁtness. Among modern executives, agreeableness is negatively related to achieved remuneration and status (Boudreau, Boswell, & Judge, 2001), and creative accomplishment (as distinct from creative potential) is negatively related to agreeableness (King, Walker, & Broyles, 1996). Though it is an uncomfortable truth to recognize, it is unlikely that ﬁtness is unconditionally maximized by investing energy in positive attention to others. Instead, though an empathic cognitive style may be useful in the whirl of social life, it may have costs in terms of exploitation or inattention to personal ﬁtness gains.
Moreover, sociopaths, who are low in agreeableness, may at least sometimes do very well in terms of ﬁtness, especially when they are rare in a population (Mealey, 1995). The balance of advantages between being agreeable and looking after personal interests will obviously vary enormously according to context. For example, in a small isolated group with a limited number of people to interact with and a need for common actions, high agreeableness may be selected for. Larger, looser social formations, or situations in which the environment allows solitary foraging, may select agreeableness downward.
This article has had several purposes. The ﬁrst has been to stress that heritable variation is ubiquitous in wild populations and therefore should be expected as the normal outcome of evolutionary processes acting on human behavioral tendencies. Thus, personality variation can be understood in the context of a large literature, both theoretical and empirical, on variation in other species.
Second, I have suggested that a fruitful way of looking at variation is in terms of trade-offs of different ﬁtness beneﬁts and costs (summarized in Table 1 for the Big Five personality factors). Theories based on trade-offs have been very successful in providing an understanding of evolution in other species. Moreover, the idea of trade-offs can be usefully married to the notion of ﬂuctuating selection to explain the persistence of diversity. Such accounts are not speculative. Studies such as those on great tits, guppies, ﬁnches, and sunﬁsh (see the section on Evolution of Variation) have demonstrated how ﬂuctuations in environmental context change the ﬁtness outcomes associated with particular phenotypes, which in turn affects the future shape of the population through natural selection. Thus, researchers examining nonhuman variation have been able to go well beyond post hoc explanations and actually observe evolution in action. The current trade-off account builds on the ideas of MacDonald (1995), who argued that the observed range of variation represents the range of viable human behavioral strategies and who stressed that there are ﬁtness disadvantages at the extremes. Thus, he stressed stabilizing selection. The present argument is that selection can ﬂuctuate, such that it may sometimes be directional for increasing a trait and sometimes be directional for decreasing it. Among the great tits, for example, selection on exploration is clearly directional in any given year (Dingemanse et al., 2004). The retention of a normal distribution is a consequence of the inconsistency of the direction of selection, not its stabilizing form. That said, I agree with MacDonald that there could be quite general disadvantages at the extremes of some personality dimensions, such as chronic depression with high neuroticism, or obsessive–compulsive personality disorder with high conscientiousness. It is not a necessary feature of the current approach that there always be stabilizing effects. The other major difference between the current approach and that of MacDonald (1995) is that he did not fully develop the notion of trade-offs across the middle range of a continuum, and in particular, he did not develop empirical predictions for the nature of trade-offs for all the different ﬁve-factor dimensions. It is important to stress that trade-offs and ﬂuctuating selection are not the only possible approaches to the maintenance of heritable variation. Biologists have also observed that there are a number of traits that are unidirectionally correlated with ﬁtness and yet in which substantial heritable variation is maintained (Rowe & Houle, 1996). An example would be physical symmetry. In general, the more symmetrical an individual, the higher its ﬁtness, and yet heritable variation in symmetry persists. The maintenance of variation in such cases appears paradoxical, because directional selection might be expected to home in on perfect symmetry and winnow out all variation. The solution to the paradox appears to be that such global traits as symmetry are affected by mutations to many, if not most, genes. Most mutations that arise are to some extent deleterious, so deviation from physical symmetry becomes an index of the load of mutations an individual is carrying.
Selection, particularly that operating via mate choice, favors symmetry, and thus individual deleterious mutations are winnowed from the population. However, so many genes are involved that there is a constant stream of new mutations maintaining population diversity. Thus, symmetry is a ﬁtness indicator trait in that it is a reliable signal of genetic quality. Some heritable human traits may be better explained by ﬁtness indicator theory than by trade-off theory. Miller (2000b), for example, has applied such reasoning to intelligence. Intelligence is correlated with physical symmetry, (reallsuggesting that it taps overall quality (Prokosch, Yeo, & Miller, 2005). Thus, a ﬁtness indicator approach seems likely to be fruitful in such a case. For personality, however, I suggest that an evolutionary trade-off account is likely to be useful. This does not mean that all personality differences are to be explained by the same mechanism. There are likely to be developmental calibration effects, too, as indicated by behavior genetics data showing a role for the unique environment and also as suggested by recent studies on early life stress and adult behavior (Figueredo et al., 2005). However, for the heritable basis of personality, the combination of trade-off and genetic polymorphism seems a fruitful avenue to pursue. It might be objected that the particular costs and beneﬁts put forward here are speculative and as such amount to just-so stories about how personality variation has arisen. The former is true; as for the latter, such a charge misunderstands the utility of adaptive explanation in psychology. The evolutionary framework used here is hypothesis generating. That is, an article such as this one, which draws on evolutionary biology, is not an end in itself but rather an engine for generating testable empirical ideas.
The particular costs and beneﬁts listed here may not turn out to be the correct ones. However, the framework makes testable predictions that would not have been arrived at inductively. For extraversion, the hypothesis that high scorers will have greater numbers of sexual partners but more serious injuries has already been conﬁrmed (Nettle, 2005). For neuroticism, the current framework makes the prediction that performance on certain types of perceptual monitoring tasks, such as detecting an artiﬁcial predator, will actually be improved by neuroticism. Because neuroticism impairs performance on many kinds of tasks, this is a novel prediction.
For openness, the model predicts that high scorers will either be socially successful through creative activity or be socially and culturally marginalized through bizarre beliefs, (who decides which beliefs are “bizarre beliefs? This is highly culturally and individually determined) and the determinants of which outcome prevails may depend on overall condition. This is a hypothesis that certainly merits further investigation (see Nettle & Clegg, 2006).
For conscientiousness, the model predicts that high scoring individuals might perform badly on tasks in which they have to respond spontaneously to changes in the affordances of the local environment, because they will be rigidly attached to previously deﬁned goals. Finally, for agreeableness, the theory predicts that high scorers will avoid being victims of interpersonal conﬂict but may often emerge as suckers in games such as the public goods game and the iterated prisoner’s dilemma game, which are well studied by psychologists and in which the usual equilibrium is a mixture of cooperation and exploitation. Thus, the current framework should be seen not as a post hoc explanation of the past but as an engine of predictions about the consequences of dispositional variation in the present. Such consequences are a central explanatory concern of personality psychology, and as such, the evolutionary framework, with its emphasis on costs, beneﬁts, and trade-offs, could be of great utility.