Original Article
Seven dimensions of personality pathology are under sexual selection in modern Spain

https://doi.org/10.1016/j.evolhumbehav.2015.10.004Get rights and content

Abstract

Personality variation is increasingly thought to have an adaptive function. This is less clear for personality disorders (PDs)—extreme variants of personality that cause harm in most aspects of life. However, the possibility that PDs may be maintained in the population because of their advantages for fitness has been not convincingly tested. In a sample of 959 outpatients, we examined whether, and how, sexual selection acts on the seven main dimensions of personality pathology, taking into account mating success, reproductive success, and the mediating role of status. We find that, to varying extents, all personality dimensions are under sexual selection. Far from being predominantly purifying, selective forces push traits in diverging, often pathological, directions. These pressures differ moderately between the sexes. Sexual selection largely acts in males through the acquisition of wealth, and through the duration (rather than the number) of mates. This gives a reproductive advantage to males high in persistence–compulsivity. Conversely, because of the decoupling between the number of mates and offspring, the promiscuous strategy of psychopaths is not so successful. Negative emotionality, the most clinically detrimental trait, is slightly deleterious in males but is positively selected in females, which can help to preserve variation. The general picture is that at least some PDs form part of high-risk alternative strategies, although a sole evolutionary mechanism is unlikely to apply to all traits. An evolutionary perspective on PDs can provide a better understanding of their nature and causes than we have achieved to date by considering them as illnesses.

Introduction

The idea that personality disorders (PDs) are alternative strategies rather than illnesses is gaining ground (Brüne et al., 2010, Troisi, 2005). Although it is mostly believed that psychopaths have dysfunctional self-regulation and affiliation systems, it has also been proposed that they may be implementing a successful sociosexual strategy based on promiscuity and exploitation (Glenn et al., 2011, Jonason et al., 2009, Mealey, 1995). Schizotypy may be a milder form of schizophrenia, but some schizotypal features may function as a fitness indicator signaling good quality to potential mates (Del Giudice, 2014, Nettle and Clegg, 2006). In addition the recurrent fears and miseries of many neurotic patients may result either from the dysregulation of alarm circuits or from their normal, survival-enhancing operation (Bateson et al., 2011, Ein-Dor et al., 2010, Lafreniere, 2009, Nesse, 2001a). At present, we lack data to establish whether certain maladaptive personalities really are failures or in fact high-risk shortcuts to fitness.

Increasingly, the evidence suggests that normal-range personality variation has adaptive functions rather than being random noise around a behavioral optimum (Bergmüller and Taborsky, 2010, Buss, 2009, Kight et al., 2013, Réale et al., 2010, Sih et al., 2004, Wolf and Weissing, 2010). This variation largely takes place along the same universal axes from insects to humans (Gosling & John, 1999); it is moderately heritable (Bouchard, 2004, Penke et al., 2007); and it has a substantial impact on resource acquisition, mating, reproduction, and survival (Ozer and Benet-Martínez, 2006, Roberts et al., 2007, Smith and Blumstein, 2008). In consequence, personality must be subject to the same selective pressures as many other traits (Stearns, Byars, Govindaraju, & Ewbank, 2010). As personality ultimately is the axial organization of enduring motivations, emotions, cognitions and behaviors that determine the effective adaptation to the environment (DeYoung, 2015, MacDonald, 2012), it may even be a major target for selection.

All the above is harder to defend in the case of PDs, extreme personality traits that cause problems in everyday living. Inordinate levels of any trait—anxiousness, impulsivity, asociality, aggressiveness, eccentricity—have been reported to harm career opportunities, social adaptation, family life, health, longevity, and well-being (Tyrer, Reed, & Crawford, 2015). Significantly, PDs shorten life expectancy by about 18 years (Fok et al., 2012), so their permanence in the population, without being eroded by selection, is a conundrum (Keller and Miller, 2006, Troisi, 2005). Nevertheless, their maladaptivity is not undisputed: the detrimental consequences are not the same for all pathological traits (Ullrich et al., 2007, Vall et al., 2015), nor is clinical adaptation the same as biological fitness (Nesse, 2001b). For example, unlike most other mental disorders, PDs do not globally harm reproductive success (Keller & Miller, 2006), and some subtypes definitely enhance resource accrual or multiply mating success (Gutiérrez et al., 2013, Sansone et al., 2011, Ullrich et al., 2007). It is our contention that studying PDs is essential to evolutionary psychology not only because of their high prevalence (about 10% of us have extreme traits, Tyrer et al., 2015) but also because examining the entire range of phenotypic variation, beyond normal-range traits, may provide a fuller picture of the evolutionary dynamics of personality. Indeed, if personality is about deleterious variation around an optimum, subjects with PDs will be the most maladapted; if it is about alternative strategies, they will be the most extreme strategists. In either case, PDs hold unique keys to understand why we are all different, and why some of these differences bring trouble.

To date, the possibility that personality traits are under sexual selection has not been studied in depth (Schuett, Tregenza, & Dall, 2010). Sexual selection favors those traits that enhance access to mates. The literature has identified it as the strongest selective force in nature, as mating success impacts on reproductive output more directly than any other component of fitness (Geher et al., 2008, Kingsolver and Diamond, 2011). In fact, sexual selection can spread traits even if they reduce survival chances (Fritzsche and Booksmythe, 2013, Hosken and House, 2011, Jones and Ratterman, 2009). In humans, height, body shape, physical attractive, voice pitch, or masculinity have shown some evidence of being under sexual selection (Hill et al., 2013, Jokela, 2009, Stulp et al., 2013). Similarly, traits like psychopathy, aggressiveness, anxiousness, extraversion, eccentricity, insecure attachment and narcissism have been hypothesized to enhance mating success or to form part of alternative sexual strategies (Belsky, 2012, Ein-Dor et al., 2010, Holtzman and Donnellan, 2015, Holtzman and Strube, 2011, Lafreniere, 2009, Nettle, 2006, Nettle and Clegg, 2006). Unfortunately, the evidence regarding the most fundamental aspects is very limited: whether and how sexual selection really affects personality; which evolutionary processes (mutation-selection balance, tradeoffs, fluctuating selection, frequency-dependent selection, condition-dependent selection) are at work (Buss, 2009, Kight et al., 2013, Wolf and Weissing, 2010); whether selective forces are similar or different in each sex (Fritzsche & Booksmythe, 2013); what mechanisms (number of mates, earlier reproduction, stable relationships, status, wealth, prestige) mediate the relationships between personality and fitness (Berg et al., 2013, Lyon and Montgomerie, 2012); and whether the answers to all the above questions are the same or different for each personality trait.

To approach these questions, we use an improved personality pathology system (Gutiérrez, Vall, Peri, Gárriz, & Garrido, 2014). This system overcomes the limitations of traditional psychiatric diagnoses, which are poorly conceived mixtures of heterogeneous traits (Widiger & Trull, 2007). For example, we know that borderline PD doubles the number of sexual partners (Sansone et al., 2011) but not which of its constituent traits—impulsivity, negative emotionality, insecure attachment, aberrant perceptions—account for this effect. The system is also comprehensive, covering previously underexplored traits as well as the pathological extremes of each trait. Indeed, although extraversion has been shown to increase fitness and neuroticism to decrease it (Jokela et al., 2011, Roberts et al., 2007), we lack information on other important traits, and results in normal-range traits do necessarily say anything about extreme variants. Finally, this model is in line both with forthcoming taxonomies (Tyrer et al., 2015) and with evolutionarily-based classificatory proposals (DeYoung, 2015, MacDonald, 2012). On the other hand, in the present study we try to look deeper into some previously neglected aspects (Fritzsche and Booksmythe, 2013, Jones and Ratterman, 2009, Schuett et al., 2010). We measured a wide range of life history variables encompassing mating success, reproductive success and status/wealth; we analyzed selective pressures separately in both sexes; we examined the strength of directional, stabilizing, disruptive, and correlational selection on mating and reproduction; and we traced the entire path from personality to status, to mating success, and to reproductive success.

Our aim is to know whether, and how, sexual selection acts on personality pathology. To this end, in a sample of 959 outpatients we examined a comprehensive set of pathological dimensions and explored which ones bring advantages for either mating or reproduction, in which sex, and through which evolutionary processes and mediating mechanisms. In this way we seek to extend previous knowledge of the evolutionary nature of pathological personalities and of the causes of its persistence in the population.

Section snippets

Participants

The sample was composed of 959 outpatients aged 16 to 67 (mean 34.5, SD 10.7), 53% female, consecutively referred to the Personality Disorder Unit of a General Hospital in Barcelona during a 6-year period. A quarter of the sample were currently studying. Among those employed, 19.9% were skilled and 33.0% were semiskilled workers. The sample did not differ from the general Spanish population in key parameters such as study level, salary, or average maternal age (www.ine.es). However, it was a

Sex differences in personality and life history

Differences between males and females were generally small (Table 1). Males showed lower negative emotionality than females, as well as higher asociality, impulsivity, and antagonism. They also had significantly more short-term mates and fewer long-term mates, with no differences in the duration of the longest relationship. Reproduction began earlier in females, but reproductive output was the same across the sexes. As for variability, standard deviation was greater in males for short-term

Personality pathology is under sexual selection

Our results show that, to varying extents, each of our seven dimensions of personality pathology is under sexual selection. Selective pressures are not homogeneously purifying, as would be expected if they were diseases (Keller & Miller, 2006). Instead, some dimensions are selected for, others against, and still others show tradeoffs, either between fitness costs and benefits or between the sexes. Thus, whereas evolutionary forces contribute to the maintenance of some pathological traits, no

Conflicts of interest

None.

Supplementary Materials

The following are the Supplementary data to this article.

Supplementary material

Acknowledgments

This work was partially supported by grants from Spain's Ministerio de Educación y Ciencia (FIS 07/0033 and ETES 08/90434) awarded to F. Gutiérrez.

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