The origins of extraversion: joint effects of facultative calibration and genetic polymorphism

The origins of variation in extraversion are largely mysterious. Recent theories and some findings suggest that personality variation can be orchestrated by specific genetic polymorphisms. Few studies, however, have examined an alternative hypothesis that personality traits are facultatively calibrated to variations in other phenotypic features, and none have considered how these distinct processes may interact in personality determination. Since physical strength and physical attractiveness likely predicted the reproductive payoffs of extraverted behavioral strategies over most of human history, it was theorized that extraversion is calibrated to variation in these characteristics. Confirming these predicted patterns, strength and attractiveness together explained a surprisingly large fraction of variance in extraversion across two studies--effects that were independent of variance explained by an androgen receptor gene polymorphism. These novel findings initially support an integrative model wherein facultative calibration and specific genetic polymorphisms operate in concert to determine personality variation.     

On the Universality of Human Nature and the Uniqueness of the Individual: The Role of Genetics and Adaptation

The concept of a universal human nature, based on a species-typical collection of complex psychological adaptations, is defended as valid, despite the existence of substantial genetic variation that makes each human genetically and biochemically unique. These apparently contradictory facts can be reconciled by considering that (a) complex adaptations necessarily require many genes to regulate their development, and (b) sexual recombination makes it improbable that all the necessary genes for a complex adaptation would be together at once in the same individual, if genes coding for complex adaptations varied substantially between individuals. Selection, interacting with sexual recombination, tends to impose relative uniformity at the functional level in complex adaptive designs, suggesting that most heritable psychological differences are not themselves likely to be complex psychological adaptations. Instead, they are mostly evolutionary by-products, such as concomitants of parasite-driven selection for biochemical individuality. An evolutionary approach to psychological variation reconceptualizes traits as either the output of species-typical, adaptively designed development and psychological mechanisms, or as the result of genetic noise creating perturbations in these mechanisms.     

Resolving the paradox of common, harmful, heritable mental disorders: which evolutionary genetic models work best?

Given that natural selection is so powerful at optimizing complex adaptations, why does it seem unable to eliminate genes (susceptibility alleles) that predispose to common, harmful, heritable mental disorders, such as schizophrenia or bipolar disorder? We assess three leading explanations for this apparent paradox from evolutionary genetic theory: (1) ancestral neutrality (susceptibility alleles were not harmful among ancestors), (2) balancing selection (susceptibility alleles sometimes increased fitness), and (3) polygenic mutation-selection balance (mental disorders reflect the inevitable mutational load on the thousands of genes underlying human behavior). The first two explanations are commonly assumed in psychiatric genetics and Darwinian psychiatry, while mutation-selection has often been discounted. All three models can explain persistent genetic variance in some traits under some conditions, but the first two have serious problems in explaining human mental disorders. Ancestral neutrality fails to explain low mental disorder frequencies and requires implausibly small selection coefficients against mental disorders given the data on the reproductive costs and impairment of mental disorders. Balancing selection (including spatio-temporal variation in selection, heterozygote advantage, antagonistic pleiotropy, and frequency-dependent selection) tends to favor environmentally contingent adaptations (which would show no heritability) or high-frequency alleles (which psychiatric genetics would have already found). Only polygenic mutation-selection balance seems consistent with the data on mental disorder prevalence rates, fitness costs, the likely rarity of susceptibility alleles, and the increased risks of mental disorders with brain trauma, inbreeding, and paternal age. This evolutionary genetic framework for mental disorders has wide-ranging implications for psychology, psychiatry, behavior genetics, molecular genetics, and evolutionary approaches to studying human behavior.     

Born to kill? A critical evaluation of homicide adaptation theory

Given the enormous harm that results from the intentional killing of humans by other humans, the development of etiological theories of homicide is an important task. Homicide Adaptation Theory (HAT) is one such attempt to explain why homicide occurs. In short, the proponents of HAT propose that humans possess a number of specific, evolved adaptations for killing that have been selected for because they managed to successfully solve recurrent adaptive problems in our ancestral past. In this paper it is argued that, although evolutionary approaches can potentially advance our understanding of homicide in important ways, the available evidence does not support the existence of specific adaptations for killing in humans. Specifically, I argue that the proponents of HAT have not provided: (a) a thorough analysis of the evolutionary costs and benefits of killing; (b) evidence for ‘special design’ features of homicide; or (c) a systematic comparative appraisal of killing among different species. Given this lack of evidence, HAT suffers in terms of its explanatory worth, relative to alternative evolutionary hypotheses, such as the idea that homicide is a by-product of other evolved adaptations.     

Accounting for the shared environment in cognitive abilities and academic achievement with measured socioecological contexts

Behavioral and molecular genetic research has established that child cognitive ability and academic performance are substantially heritable, but genetic variation does not account for all of the stratification of cognitive and academic outcomes across families. Which specific contexts and experiences contribute to these shared environmental influences on cognitive ability and academic achievement? Using an ethnically and socioeconomically diverse sample of N = 1728 twins ages 7–20 from the Texas Twin Project, we identified specific measured family, school, and neighborhood socioecological contexts that statistically accounted for latent shared environmental variance in cognitive abilities and academic skills. Composite measures of parent socioeconomic status (SES), school demographic composition, and neighborhood SES accounted for moderate proportions of variation in IQ and achievement. Total variance explained by the multilevel contexts ranged from 15% to 22%. The influence of family SES on IQ and achievement overlapped substantially with the influence of school and neighborhood predictors. Together with race, the measured socioecological contexts explained 100% of shared environmental influences on IQ and approximately 79% of shared environmental influences on both verbal comprehension and reading ability. In contrast, nontrivial proportions of shared environmental variation in math performance were left unexplained. We highlight the potential utility of constructing “polyenvironmental risk scores” in an effort to better predict developmental outcomes and to quantify children's and adolescents’ interrelated networks of experiences. A video abstract of this article can be viewed at: https://youtu.be/77E_DctFsr0     

Evolutionary psychology and consumer behavior: A constructive critique

We examine the theoretical basis for the evolutionary narrative common to the target papers by Saad (this issue) and by Griskevicius and Kenrick (this issue) and identify areas of controversy that have sparked debate about evolutionary psychology [EP] among biologists and behavioral ecologists. The two main areas of disagreement are over (1) the role of genetic adaptations resulting from natural selection in ancient times compared to other forces leading to current behavior; and (2) the likelihood that evolution resulted in a set of highly specialized mental modules or information-processing circuits thought to be instrumental in determining present-day behavior. We review the EP research discussed by the authors of the target papers as a means of evaluating the evidence in support of the theory and of suggesting future directions of research.     

The importance of traits and abilities in supervisors' hirability decisions as a function of method of assessment

Past research on the importance of traits and abilities in supervisors' hirability decisions has ignored the influence of the selection method used to derive information about these traits and abilities. In this study, experienced retail store supervisors (N=163) rated job applicant profiles that were described on the Big Five and General Mental Ability (GMA) personality dimensions. Contrary to past studies, the supervisors were also informed about the method of assessment used (paper‐and‐pencil test vs. unstructured interview). Hierarchical linear modelling analyses showed that the importance attached to extraversion and GMA was significantly moderated by the selection method, with extraversion and GMA decreasing in importance when store supervisors knew that scores on extraversion and GMA were derived from a paper‐and‐pencil test as opposed to from an unstructured interview. Store supervisors with more selection‐related experience also attached more importance to GMA. Results are discussed in relation to the practice–science gap and the extant literature on perceptions of selection procedures.     

The stress response systems: Universality and adaptive individual differences

Biological reactivity to psychological stressors comprises a complex, integrated system of central neural and peripheral neuroendocrine responses designed to prepare the organism for challenge or threat. Developmental experience plays a role, along with heritable variation, in calibrating the response dynamics of this system. This calibration occurs through setting of response thresholds in the regulatory mechanisms that coordinate the expression and use of trait-specific gene products and environmental elements that build alternative phenotypes. Whereas natural selection tends to favor developmental plasticity when the fitness of alternative phenotypes can be predicted from observable cues, genetic polymorphisms are most likely to be maintained when the advantages of niche specialization are high and organisms can evaluate and select their niches. Well-developed theories of both adaptive phenotypic plasticity and adaptive genetic variation in the stress-response systems have been advanced in the literature. Taken together, these theories strongly suggest that variation in stress-response phenotypes has been shaped by natural selection, is an adaptation to multiniche environments, and involves an integration of genetic influences and condition-sensitivity.     

Personality characteristics that are valued in teams: Not always “more is better”?

This study investigates the relationships between personality traits and contributions to teamwork that are often assumed to be linear. We use a theory‐driven approach to propose that extraversion, agreeableness and conscientiousness have inverted U‐shaped relationships with contributions to teamwork. In a sample of 220 participants asked to perform a creative task in teams, we found that extraversion, agreeableness and conscientiousness were curvilinearly associated with peer‐rated contributions to teamwork in such a way that the associations were positive, with a decreasing slope, up to a peak, and then they became negative as personality scores further increased. We replicated the results concerning the non‐linear association between extraversion, conscientiousness and peer‐rated contributions to teamwork in a sample of 314 participants engaged in a collaborative learning exercise. Our results support recent claims and empirical evidence that explorations of personality–work‐related behaviours relationships should move beyond the linearity assumptions. We conclude by discussing the implications of our research for personnel selection.     

Évaluer le fonctionnement optimal : échelles de psychologie positive validées en langue française

Positive psychology research studies have lead to greater consideration and promotion of optimal functioning in the different fields of psychology. This article introduces an epistemological questioning about optimal functioning assessment and practical considerations on the use of existing psychopathology scales which can be reinterpreted in order to assess well-being and positive characteristics (if one considers human psychology as a continuum going from disorders to optimal functioning), and the use of existing questionnaires measuring specific positive personality traits (if one considers that the continuum theory may not explain all the phenomena observed). The authors present a selection of questionnaires validated in French, which can be used for research studies and clinical practice.     

A behavior genetic analysis of personality and loneliness

The phenotypic, genetic, and environmental correlations between the Big Five factors of personality and loneliness were examined. At the phenotypic level, loneliness had a strong significant positive correlation with neuroticism, significant moderate negative correlations with agreeableness, conscientiousness, and extraversion, and a small positive correlation with openness. Both loneliness and personality were found to be heritable. Bivariate genetic analyses resulted in significant positive genetic correlations between loneliness and neuroticism and openness, and significant negative genetic correlations with agreeableness, conscientiousness, and extraversion. Significant unique environment correlations were found between loneliness and four of the five personality factors (all negative except neuroticism) and a non-significant correlation with openness. The results suggest common genetic and unique environmental factors play a role in personality and loneliness.     

The benefits of youth

We examine human psychological development from an evolutionary perspective and propose that some aspects of developmental immaturity have been selected for their adaptive value either for individuals at a specific time in development (ontogenetic adaptations) or as preparation for adulthood (deferred adaptations). We review research and theory on the possible adaptive role of immaturity in human development, focusing on play, neural plasticity, and cognitive limitations that may foster the development of sensory systems, learning/education, and caretaking by adults. We argue that considering the possible adaptive features of immaturity, along with the obvious maladaptive ones, provides a more accurate picture of ontogeny and ways to foster healthy psychological development.     

Constructive criticism: An evaluation of Buller and Hardcastle's genetic and neuroscientific arguments against Evolutionary Psychology

David Buller and Valerie Hardcastle have argued that various discoveries about the genetics and nature of brain development show that most “central” psychological mechanisms cannot be adaptations because the nature of the contribution from the environment on which they are based shows they are not heritable. Some philosophers and scientists have argued that a strong role for the environment is compatible with high heritability as long as the environment is highly stable down lineages. In this paper I support this view by arguing that the discoveries Buller and Hardcastle refer to either do not show as strong a role for the environment as they suggest, or these discoveries show that the brain's developmental process depends in many cases on input from the environment that is highly stable across generations.     

The mediating role of work climate perceptions in the relationship between personality and performance

Although past research has demonstrated a link between personality and job performance, potential enabling factors of this relationship have yet to be explored comprehensively. We hypothesized that perceptions of work climate, specifically relationship dimensions—cohesion, supervisor support, and job involvement—might be the mechanism through which the relationship between personality and job performance can be explained. Two hundred and thirty Australian employees completed an online survey measuring personality, relationship dimensions of work climate (job involvement, coworker cohesion, and supervisor support) and job performance. Results revealed that the relationship dimensions of work climate fully mediated the relationship between agreeableness and job performance, and extraversion and job performance, while the relationship between neuroticism and job performance was partially mediated by relationship dimensions of work climate. Supervisor support primarily accounted for this mediated effect for the neuroticism–job performance relationship, whereas for extraversion only job involvement explained significant unique variance. Our findings suggest that the relationship of agreeableness, extraversion, and neuroticism with job performance is indirect, and perceptions of the work environment itself play a role in this relationship. This implies that organizations should consider the work environment, in addition to personality during selection procedures. Future research should examine whether different levels of work environment dimensions, foster greater job performance in employees.     

Neuroticism, extraversion, and related traits in adult twins reared apart and reared together

The relative importance of genetic and environmental factors for neuroticism, extraversion, impulsivity, and monotony avoidance were estimated in a sample of 99 monozygotic and 229 dizygotic pairs of twins reared apart (TRA) and a matched sample of 160 monozygotic and 212 dizygotic pairs of twins reared together (TRT). The average age was 58.6 (SD = 13.6); 72% of the twins were 50 or older. Model-fitting analyses verified the importance of genetic factors for all four measures; from 23% to 45% of the total variation was attributable to genetic sources. There was considerable evidence that these factors were operating in a nonadditive manner for extraversion and impulsivity. Shared environment accounted for less than 10% of the variance; some evidence for selective placement was found for neuroticism.     

What gene-environment interactions can tell us about social competence in typical and atypical populations

Social competence is a complex human behaviour that is likely to involve a system of genes that interacts with a myriad of environmental risk and protective factors. The search for its genetic and environmental origins and influences is equally complex and will require a multidimensional conceptualization and multiple methods and levels of analysis. Behavioural genetic research can begin to address the fundamental yet complex question of how children develop social competence by uncovering the various influences on social development and disentangling variance due to multiple genes, environments and experiences. In this paper, we review the current status of research on sociability, face recognition, emotion recognition, and theory of mind (TOM)--well defined and measured constructs that are likely to be useful indices for detecting genetic and environmental influences on social competence. We also propose specific milestones as indices of further progress in the field: the development of an operational definition of the construct of social competence, the identification of social endophenotypes-psychological processes that are validly and reliably measured components of social competence, and improving specificity and homogeneity with regard to social endophenotypes within a population of study by employing 'extreme social phenotypes'. These efforts will lead to a better understanding of the specific contributions to the normal variation of social competence in the general population as well as to atypical social development.     

Chimpanzees demonstrate individual differences in social information use

Studies of transmission biases in social learning have greatly informed our understanding of how behaviour patterns may diffuse through animal populations, yet within-species inter-individual variation in social information use has received little attention and remains poorly understood. We have addressed this question by examining individual performances across multiple experiments with the same population of primates. We compiled a dataset spanning 16 social learning studies (26 experimental conditions) carried out at the same study site over a 12-year period, incorporating a total of 167 chimpanzees. We applied a binary scoring system to code each participant’s performance in each study according to whether they demonstrated evidence of using social information from conspecifics to solve the experimental task or not (Social Information Score—‘SIS’). Bayesian binomial mixed effects models were then used to estimate the extent to which individual differences influenced SIS, together with any effects of sex, rearing history, age, prior involvement in research and task type on SIS. An estimate of repeatability found that approximately half of the variance in SIS was accounted for by individual identity, indicating that individual differences play a critical role in the social learning behaviour of chimpanzees. According to the model that best fit the data, females were, depending on their rearing history, 15–24% more likely to use social information to solve experimental tasks than males. However, there was no strong evidence of an effect of age or research experience, and pedigree records indicated that SIS was not a strongly heritable trait. Our study offers a novel, transferable method for the study of individual differences in social learning.     

The genetic basis of entrepreneurship: Effects of gender and personality

Extending previous research on the genetic underpinnings of entrepreneurship, we investigate gender differences in the genetic influences on the tendency of people to become entrepreneurs. We also examined two mediating variables through which genetic factors may impact this tendency: extraversion and neuroticism. Based on 1285 pairs of identical twins (449 male and 836 female pairs) and 849 pairs of same-sex fraternal twins (283 male and 566 female pairs), we found that females have a strong genetic influence and zero shared-environmental influences on their tendency to become entrepreneurs. In contrast, males show zero genetic influence, but a large shared-environmental influence. Extraversion and neuroticism mediate the genetic influences on women’s tendency to become entrepreneurs, whereas extraversion mediates shared-environmental influences on men’s tendency to become entrepreneurs. We discuss this sharp difference in genetic influences on entrepreneurship across gender groups and highlight the different challenges that men and women face in their entrepreneurial endeavors.     

Is Adolescent Bullying an Evolutionary Adaptation?

Bullying appears to be ubiquitous across cultures, involving hundreds of millions of adolescents worldwide, and has potentially serious negative consequences for its participants (particularly victims). We challenge the traditionally held belief that bullying results from maladaptive development by reviewing evidence that bullying may be, in part, an evolved, facultative, adaptive strategy that offers some benefits to its practitioners. In support of this view, we draw from research that suggests bullying serves to promote adolescent bullies' evolutionarily-relevant somatic, sexual, and dominance goals, has a genetic basis, and is widespread among nonhuman animals. We identify and explain differences in the bullying behavior of the two sexes, as well as when and why bullying is adaptive and when it may not be. We offer commentary on both the failures and successes of current anti-bullying interventions from an evolutionary perspective and suggest future directions for both research and anti-bullying interventions.