An evolutionary approach to the extraversion continuum

The prospective power of personality for childbearing: a longitudinal study based on data from Germany

The link between personality and fertility is relatively underexplored. Moreover, there are only a few studies focusing on the prospective association between personality and childbearing. However, none of these studies considered the Five-Factor Model (FFM), which is the most widely accepted measurement of personality. The present study fills this gap by examining the prospective association between the FFM and the hazard ratio of the first and the second childbirth in Germany. Analyses are based on recent data (2005–2017) from the Socio-economic Panel Study. Cox proportional hazard models are applied. Findings demonstrate that personality traits are associated with fertility. Extraversion is positively linked with the first childbirth, but is negatively associated with the second childbirth. These findings are mainly driven by males. Agreeableness is positively linked with the first childbirth across the total sample. Again, this correlation is mainly based on the findings for men, among whom a positive association between agreeableness and the second childbirth is also found. Among women, personality does not seem to be linked with the first childbirth. However, the risk of having a second child is found to be negatively associated with conscientiousness. My study adds to the current understanding of the personality–fertility association by exploring the impact of personality trait scores from the FFM on subsequent fertility behavior. However, further research is needed on the association between personality and childbearing; on the mechanisms through which personality affects fertility; and on how these links differ across cultures, among higher parities, and for births after re-partnering.

Personality Trait Patterns Moderate the Simple Model of Environmental Citizenship

The current study investigates the Simple Model of Environmental Citizenship (SMEC) in a representative sample of Lithuanian emerging adults. The SMEC is a practical model of assessing environmental citizenship and is intended to be simple to use in interventions and longitudinal research. A total of 700 individuals (50% female) with a mean age of 30.6 years participated in the survey. The participants filled in a questionnaire comprising measures assessing all the components of the SMEC as well as a personality trait measure. Participants were clustered by their personality traits and the resulting profiles were used as a moderator for the SMEC. The results revealed that the SMEC functions differently for individuals possessing different personality trait patterns and that in order to promote environmental citizenship or to engage in education for environmental citizenship, different strategies might be more effective for different individuals.

The evolution of personality disorders: A review of proposals

Personality disorders (PDs) are currently considered dysfunctions. However, personality differences are older than humanity and are ubiquitous in nature, from insects to higher primates. This suggests that a number of evolutionary mechanisms-other than dysfunctions-may be able to maintain stable behavioral variation in the gene pool. First of all, apparently maladaptive traits may actually improve fitness by enabling better survival or successful mating or reproduction, as exemplified by neuroticism, psychopathy, and narcissism. Furthermore, some PDs may harm important biological goals while facilitating others, or may be globally beneficial or detrimental depending on environmental circumstances or body condition. Alternatively, certain traits may form part of life history strategies: Coordinated suites of morphological, physiological and behavioral characters that optimize fitness through alternative routes and respond to selection as a whole. Still others may be vestigial adaptations that are no longer beneficial in present times. Finally, variation may be adaptative in and by itself, as it reduces competition for finite resources. These and other evolutionary mechanisms are reviewed and illustrated through human and non-human examples. Evolutionary theory is the best-substantiated explanatory framework across the life sciences, and may shed light on the question of why harmful personalities exist at all.

Toward the Development and Validation of a Model of Environmental Citizenship of Young Adults

Growing civic participation in environmental movements shows that societies are more engaging in behavior that can be described as environmental citizenship. This behavior, however, may not necessarily be driven by factual knowledge and accurate beliefs. In the present study, a simplified model of environmental citizenship proposed by Hawthorne and Alabaster is tested in a sample of Lithuanian young adults in order to develop a working model of environmental citizenship that could be later used in intervention designs as a change model. A convenience sample of 267 young adults from 18 to 40 years of age participated in the study by filling in a questionnaire that assessed various components that comprise a model of environmental citizenship. The results indicate that, with a few modifications to better fit the data, the model fit the data well and could explain approximately 50% of the variance of environmental citizenship. The study uncovered a gap between factual (concrete) environmental knowledge and environmental literacy (perceived competence), illustrating the need to address this divide in order to ensure evidence-based participation in environmental movements and environmental citizenship behavior.

Perceived Effectiveness of Flirtation Tactics: The Effects of sex, Mating Context and Individual Differences in US and Norwegian Samples

Flirting involves various signals communicated between individuals. To attract potential mates, men and women exhibit flirtatious behavior to get the attention of, and potentially elicit sexual or romantic interest from, a desired partner. In this first large, preregistered study of judgement of the effectiveness of flirtation tactics based on Sexual Strategies Theory, we considered the effects of flirter's (actor) sex and mating contexts in addition to rater's (participant) sex across two cultures, Norway and the U.S. Culturally relevant covariates such as sociosexuality, extraversion, mate value, age, and religiosity were examined. Participants from Norway (N = 415, 56% women) and the US (N = 577, 69% women) responded to one of four different randomized questionnaires representing a factorial design considering either short-term versus long-term mating context and either female or male sex of actor. We found that sexual availability cues were judged more effective when employed by women in short-term mating contexts. Friendly contact, such as hugs or kissing on the cheek, was not. Cues to generosity and commitment were judged more effective when employed by men in long-term mating contexts. Humor was rated as more effective when used by men and in long-term contexts, and least effective when used by women in short term contexts. However, laughing or giggling at someone's jokes was an effective flirtation tactic for both sexes. Overall, predictions for culturally relevant covariates were not supported, but cultural differences were found in bodily displays, initial contact, and generosity. These findings dovetail neatly with findings from the self-promotion literature, and further support that flirtation is a universal mate signaling strategy.

A meta-analysis of sex differences in animal personality: no evidence for the greater male variability hypothesis

The notion that men are more variable than women has become embedded into scientific thinking. For mental traits like personality, greater male variability has been partly attributed to biology, underpinned by claims that there is generally greater variation among males than females in non-human animals due to stronger sexual selection on males. However, evidence for greater male variability is limited to morphological traits, and there is little information regarding sex differences in personality-like behaviours for non-human animals. Here, we meta-analysed sex differences in means and variances for over 2100 effects (204 studies) from 220 species (covering five broad taxonomic groups) across five personality traits: boldness, aggression, activity, sociality and exploration. We also tested if sexual size dimorphism, a proxy for sex-specific sexual selection, explains variation in the magnitude of sex differences in personality. We found no significant differences in personality between the sexes. In addition, sexual size dimorphism did not explain variation in the magnitude of the observed sex differences in the mean or variance in personality for any taxonomic group. In sum, we find no evidence for widespread sex differences in variability in non-human animal personality.

Competing motives in a pandemic: Interplays between fundamental social motives and technology use in predicting (Non)Compliance with social distancing guidelines

During the COVID-19 pandemic, individuals were advised to adhere to social distancing guidelines limiting physical interpersonal contact. Humans have a suite of adaptations to satisfy belonging needs while avoiding diseased conspecifics. Competition between motivational systems may explain adherence and resistance to social distancing guidelines and how technologically mediated interactions further shape these decisions. This study is a preregistered analysis of data in a representative sample collected during the pandemic investigating how individual differences in affiliative and pathogen-avoidant motives predict interest in physical interactions (N = 2409). Germ aversion predicted disinterest in physical interactions and need to belong predicted interest. Additional analyses revealed technology use satisfied belonging motives that unexpectedly heightened interest in physical contact. Exploratory analyses further indicate that internet speed was similarly associated with greater interest in physical interactions. We frame these results through a competing fundamental social motives framework and discuss how to address future pandemics effectively.

Do Early Life Experiences Predict Variation in the General Factor of Personality (GFP)?

Objective

The controversial General Factor of Personality (GFP) has been proposed as an indicator of social effectiveness and a slower life history strategy. An alternative hypothesis holds that only meta-trait alpha, comprising agreeableness, conscientiousness, and emotional stability, is a slow life history indicator. This study tested whether the GFP and/or alpha emerges from both self- and stranger-ratings, and whether either is predicted by indicators of harsh childhood ecologies.

Methods

U.S. undergraduate participants (N = 366) completed a Big Five instrument, a measure of socially desirable response bias, and brief (thin slice) videotaped interviews. Raters scored the interviews using the same Big Five instrument.

Results

Structural equation modeling of the self-report data yielded a well-fitting GFP, which was positively associated with father closeness. Meta-trait alpha, based on self-report, was associated with both father closeness and neighborhood stress, but showed positive loadings only for agreeableness and emotional stability. Stranger-rating data failed to yield either a well-fitting GFP or metatrait alpha.

Conclusions

Our findings are equivocal regarding the usefulness of the GFP specifically, and higher-order personality factors generally, in evolutionary personality science.

Capital as an Integrative Conceptualisation of Human Characteristics, Behaviour, and Outcomes Predicting Reproductive Success and Evolutionary Fitness

According to evolutionary theory, human cognition and behaviour are based on adaptations selected for their contribution to reproduction in the past, which in the present may result in differential reproductive success and inclusive fitness. Because this depiction is broad and human behaviour often separated from this ultimate outcome (e.g., increasing childlessness), evolutionary theory can only incompletely account for human everyday behaviour. Moreover, effects of most studied traits and characteristics on mating and reproductive success turned out not to be robust. In this article, an abstract descriptive level for evaluating human characteristics, behaviour, and outcomes is proposed, as a predictor of long-term reproductive success and fitness. Characteristics, behaviour, and outcomes are assessed in terms of attained and maintained capital, defined by more concrete (e.g., mating success, personality traits) and abstract (e.g., influence, received attention) facets, thus extending constructs like embodied capital and social capital theory, which focuses on resources embedded in social relationships. Situations are framed as opportunities to gain capital, and situational factors function as elicitors for gaining and evaluating capital. Combined capital facets should more robustly predict reproductive success and (theoretically) fitness than individual fitness predictors. Different ways of defining and testing these associations are outlined, including a method for empirically examining the psychometric utility of introducing a capital concept. Further theorising and empirical research should more precisely define capital and its facets, and test associations with (correlates of) reproductive success and fitness.

Are cognition and personality related in budgerigars?

In recent years, researchers have been attempting to relate differences in personality (e.g., boldness, aggressiveness, exploration tendency) to variation in cognition (performances in tasks that require learning, reasoning, attention, or memory, etc.) both theoretically and empirically. However, it is unclear on what basis personality and cognition might be associated with each other. Previous theory suggests a connection between fast–slow personality types and cognitive speed–accuracy tradeoffs. In this study, we tested this hypothesis in budgerigars and found that, in their 1st associative learning, birds with fast personality (less fearful of handling stress) were fast learners in the beginning, while slow personality individuals improved faster, but both types of birds did not differ in accuracy. However, these relationships were context-dependent. No significant relationship was found in subsequent learning tasks (reversal learning and a 2nd associative learning) in the familiar context (task setup and apparatus similar to the 1st associative learning). We then conducted a problem-solving experiment with novel setup and apparatus to test 1 possible explanation that the association between personality and cognition in the 1st associative learning might be caused by noncognitive constraint, such as fearfulness when facing novel task setup and apparatus. We found that fast individuals interacted more with the problem box and solved it, whereas the slow birds were not. We suggest that personalities can influence cognitive performances and trigger a cognitive speed-improvement tradeoff under the novel context. However, there are no consistent cognitive styles that co-varied with different personalities.

No Evidence for Social Surrogacy in Fostering Intentions to Follow Social Distancing Guidelines

Abstract. We tested whether temporary social needs satisfaction through social surrogacy would ensure greater willingness to adhere to social distancing recommendations elicited by the COVID-19 pandemic. Participants were randomly assigned to social exclusion or inclusion via Cyberball ( n = 534) followed by either a social surrogacy manipulation (imagine favorite TV show), or one of two control states. No restorative effects emerged following a social surrogacy prime. An exploratory analysis considering age as a moderator ( MAge = 36.89 years, SD = 10.88, range = 19–70 years) found that excluded adults (i.e., middle and older ages) reported more intentions to deviate following surrogacy experiences relative to control experiences; no effects emerged for younger adults in this analysis. We discuss the limitations of social surrogacy in fostering compliance with social distancing initiatives.

Prevalence and characteristics of childfree adults in Michigan (USA)

Childfree individuals choose not to have children, which makes them a distinctive group from parents who have had children, not-yet-parents who plan to have children, and childless indivduals who would have liked to have children. Most research on parental status and psychosocial characteristics has not effectively distinguished childfree individuals from other non-parents or has relied on non-representative samples. In this study, we use a representative sample of 981 Michigan adults to estimate the prevalence of childfree individuals, to examine how childfree individuals differ from parents and other types of non-parents in life satisfaction, political ideology, and personality, and to examine whether childfree individuals are viewed as an outgroup. We find that over a quarter of Michigan adults identified as childfree. After controlling for demographic characteristics, we find no differences in life satisfaction and limited differences in personality traits between childfree individuals and parents, not-yet-parents, or childless individuals. However, childfree individuals were more liberal than parents, and those who have or want(ed) children felt substantially less warm toward childfree individuals than childfree individuals felt toward each other. Given the prevalence of childfree individuals, the risks of their outgroup status, and their potential role in politics as a uniquely liberal group, it is important for demographic research to distinguish the childfree from others and to better understand these individuals.

Contagious Health Risk and Precautionary Social Distancing

Background

Since humans are social animals, social relations are incredibly important. However, in cases of contagious diseases such as the flu, social contacts also pose a health risk. According to prominent health behavior change theories, perceiving a risk for one’s health motivates precautionary behaviors. The “behavioral immune system” approach suggests that social distancing might be triggered as a precautionary, evolutionarily learned behavior to prevent transmitting contagious diseases through social contact. This study examines the link between personal risk perception for an infectious disease and precautionary behavior for disease-prevention in the context of social relationships.

Methods

At 2-week intervals during the first semester, 100 Psychology freshmen indicated their flu risk perception, whether they had been ill during the previous week, and their friendships within their freshmen network for eight time points.

Results

Social network analysis revealed that participants who reported a high flu risk perception listed fewer friends (B = −0.10, OR = 0.91, p = 0.026), and were more likely to be ill at the next measuring point (B = 0.26, OR = 1.30, p = 0.005). Incoming friendship nominations increased the likelihood of illness (B = 0.14, OR = 1.15, p = 0.008), while the reduced number of friendship nominations only marginally decreased this likelihood (B = −0.07, OR = 0.93, p = 0.052).

Conclusion

In accordance with the concept of a “behavioral immune system,” participants with high flu risk perception displayed a social precautionary distancing even when in an environment, in which the behavior was ineffective to prevent an illness.

Personality and psychosocial functioning in early adolescence: Age-differential associations from the self- and parent perspective

Although psychosocial functioning and personality are indisputably interrelated in adulthood, much less is known about these associations in early adolescence. Accordingly, the goal of the current study was twofold. First, we investigated associations between adolescents’ personality and three broad indicators of psychosocial functioning: academic achievement, social relationships, and psychosocial adjustment. Second, we tested differential effects by comparing these associations across three different cohorts (Grades 5, 7, and 9) and across two raters of adolescents’ personality: self- and parent reports. Our sample consisted of N = 2667 students and their parents. According to latent regression models, adolescents’ personality traits showed significant associations with all psychosocial functioning variables: Achievement was most consistently associated with emotional stability, openness, and conscientiousness; social relationships were most consistently associated with agreeableness and conscientiousness; and psychosocial adjustment was related to all of the Big Five traits. Most associations did not vary across grades, whereas self-reported extraversion showed lower associations in later grades. Looking at rater-specific effects, we found fewer and usually smaller associations with parent- than with self-rated personality, again with the most significant differences with extraversion. We discuss the consistent interrelatedness between adolescents’ personality and psychosocial functioning but also highlight important exceptions in grade- and rater-specificities.

The demography of swiping right. An overview of couples who met through dating apps in Switzerland

Within the span of almost ten years, phone dating apps have transformed the dating scene by normalizing and, according to some voices, gamifying the digital quest for a partner. Despite amplified discussion on how swipe-based apps damage the fabric of intimate ties, scientific accounts on whether they have led to different relationship patterns are missing. Using 2018 survey data from Switzerland, this study provides a rich overview of couples who met through dating apps by addressing three main themes: 1) family formation intentions, 2) relationship satisfaction and individual well-being, and 3) assortative mating. The data indicate that in Switzerland, dating apps have recently taken over as main online dating context. Results further show that couples formed through mobile dating have stronger cohabiting intentions than those formed in non-digital settings. Women who found their partner through a dating app also have stronger fertility desires and intentions than those who found their partner offline. Generally, there are no differences between couples initiated through dating apps and those initiated elsewhere regarding relationship and life satisfaction. Though more data are needed to capture the full range of users' romantic and sexual experiences, current results mitigate some of the concerns regarding the short-term orientation or the poor quality of relationships formed through mobile dating. Findings finally suggest that dating apps play an important role in altering couple composition by allowing for more educationally diverse and geographically distant couples.

The evolutionary genetics of personality

Genetic influences on personality differences are ubiquitous, but their nature is not well understood. A theoretical framework might help, and can be provided by evolutionary genetics. We assess three evolutionary genetic mechanisms that could explain genetic variance in personality differences: selective neutrality, mutation‐selection balance, and balancing selection. Based on evolutionary genetic theory and empirical results from behaviour genetics and personality psychology, we conclude that selective neutrality is largely irrelevant, that mutation‐selection balance seems best at explaining genetic variance in intelligence, and that balancing selection by environmental heterogeneity seems best at explaining genetic variance in personality traits. We propose a general model of heritable personality differences that conceptualises intelligence as fitness components and personality traits as individual reaction norms of genotypes across environments, with different fitness consequences in different environmental niches. We also discuss the place of mental health in the model. This evolutionary genetic framework highlights the role of gene‐environment interactions in the study of personality, yields new insight into the person‐situation‐debate and the structure of personality, and has practical implications for both quantitative and molecular genetic studies of personality. Copyright © 2007 John Wiley & Sons, Ltd.

Adult temperament and childbearing over the life course

Emerging evidence suggests that temperament may predict childbearing. We examined the association between four temperament traits (novelty seeking, harm avoidance, reward dependence and persistence of the Temperament and Character Inventory) and childbearing over the life course in the population‐based Cardiovascular Risk in Young Finns study (n = 1535; 985 women, 550 men). Temperament was assessed when the participants were aged 20–35 and fertility history from adolescence to adulthood was reported by the participants at age 30–45. Discrete‐time survival analysis modelling indicated that high childbearing probability was predicted by low novelty seeking (standardized OR = 0.92; 95% confidence interval 0.88–0.97), low harm avoidance (OR = 0.90; 0.85–0.95), high reward dependence (OR = 1.09; 1.03–1.15) and low persistence (OR = 0.91; 0.87–0.96) with no sex differences or quadratic effects. These associations grew stronger with increase in numbers of children. The findings were substantially the same in a completely prospective analysis. Adjusting for education did not influence the associations. Despite its negative association with overall childbearing, high novelty seeking increased the probability of having children in participants who were not living with a partner (OR = 1.29; 1.12–1.49). These data provide novel evidence for the role of temperament in influencing childbearing, and suggest possible weak natural selection of temperament traits in contemporary humans. Copyright © 2009 John Wiley & Sons, Ltd.

Testing an Adaptationist Theory of Trait Covariation: Relative Bargaining Power as a Common Calibrator of an Interpersonal Syndrome

This article provides the first test of an adaptationist ‘common calibration’ theory to explain the origins of trait covariation, which holds that (i) personality traits are often facultatively calibrated in response to cues that ancestrally predicted the reproductive payoffs of different trait levels and (ii) distinct traits that are calibrated on the basis of common input cues will exhibit consistent patterns of covariation. This theory is applied to explain the covariation within a ‘personality syndrome’ encompassing various interpersonal trait dimensions (e.g. extraversion, emotionality and attachment styles). Specifically, it is hypothesized that these traits are inter–correlated because each is calibrated in response to relative bargaining power (RBP)—a joint function of one's ability to benefit others and harm others. Path analyses from a correlational study compellingly supported this theoretical model: Objective and self–perceived measures of RBP–enhancing phenotypic features (physical attractiveness and physical strength) influenced an internal regulatory variable indexing RBP (i.e. self–perceived RBP), which in turn had robust effects on each of the focal personality traits. Moreover, in support of the theory's core postulate, controlling for self–perceived RBP greatly reduced the covariation within the interpersonal syndrome. These novel findings illustrate the promise of an evolutionary psychological approach to elucidating trait covariation. Copyright © 2013 John Wiley & Sons, Ltd.

Evolution, genes, and inter‐disciplinary personality research

Most commentaries welcomed an evolutionary genetic approach to personality, but several raised concerns about our integrative model. In response, we clarify the scientific status of evolutionary genetic theory and explain the plausibility and value of our evolutionary genetic model of personality, despite some shortcomings with the currently available theories and data. We also have a closer look at mate choice for personality traits, point to promising ways to assess evolutionarily relevant environmental factors and defend higher‐order personality domains and the g‐factor as the best units for evolutionary genetic analyses. Finally, we discuss which extensions of and alternatives to our model appear most fruitful, and end with a call for more inter‐disciplinary personality research grounded in evolutionary theory. Copyright © 2007 John Wiley & Sons, Ltd.

The dark triad: Facilitating a short‐term mating strategy in men

This survey (N = 224) found that characteristics collectively known as the Dark Triad (i.e. narcissism, psychopathy and Machiavellianism) were correlated with various dimensions of short‐term mating but not long‐term mating. The link between the Dark Triad and short‐term mating was stronger for men than for women. The Dark Triad partially mediated the sex difference in short‐term mating behaviour. Findings are consistent with a view that the Dark Triad facilitates an exploitative, short‐term mating strategy in men. Possible implications, including that Dark Triad traits represent a bundle of individual differences that promote a reproductively adaptive strategy are discussed. Findings are discussed in the broad context of how an evolutionary approach to personality psychology can enhance our understanding of individual differences. Copyright © 2008 John Wiley & Sons, Ltd.

Behavioral Immune System Responses to Coronavirus: A Reinforcement Sensitivity Theory Explanation of Conformity, Warmth Toward Others and Attitudes Toward Lockdown

Behavioral immune system (BIS) describes psychological mechanisms that detect cues to infectious pathogens in the immediate environment, trigger disease-relevant responses and facilitate behavioral avoidance/escape. BIS activation elicits a perceived vulnerability to disease (PVD) which can result in conformity with social norms. However, a response to superficial cues can result in aversive responses to people that pose no actual threat, leading to an aversion to unfamiliar others, and likelihood of prejudice. Pathogen-neutralizing behaviors, therefore, have implications for social interaction as well as illness behaviors and responses to health communications. In this study, we investigate how PVD influences conformity, attitudes to other people and to lockdown regulations through the lens of the Reinforcement Sensitivity Theory (RST). RST describes personality in terms of biologically-driven approach and avoidance motivations which support personal goals. Participants from the United Kingdom public (N = 605) completed an RST personality questionnaire and then read either (a) coronavirus morbidity-mortality statistics and current United Kingdom government lifestyle regulations, (b) just the regulations (as presented in most government publicity materials), or (c) no information at all. They all completed the Perceived Vulnerability to Disease scale to assess BIS-relevant Germ Aversion and Perceived Infectability, followed by questions measuring social conformity, warmth toward others and attitudes toward lockdown measures. Significantly lower PVD scores were observed in the no-information condition, with the other conditions showing no difference. In terms of RST, approach behaviors related to goal-drive persistence work alongside fear in explaining conformity to social norms. Reward related approach behaviors partially explained warmth toward others, indicating that social rewards gained through interaction continue to be strong drivers of behavior. We found no role for RST traits in attitudes toward lockdown. Overall, coronavirus-related behavior is not driven purely by fear, but also by social and/or protection goals regulated by approach motivation. This study presents new insights into public perceptions of coronavirus and government regulated lifestyle restrictions, helping to explain social behaviors in terms of biologically driven mechanisms. Such understanding is vital if we are to successfully motivate public behavior to constrain spread of the virus.

What Works for Whom? Investigating Adolescents’ Pro-Environmental Behaviors

Pro-environmental behavior has been extensively studied using general models of predicting behavior; however, these models have very limited value in making inferences about individuals. To address this shortcoming, a person-oriented investigation of five pro-environmental behaviors differing in complexity was carried out using a clustering approach. A total of 863 adolescents (mean age 15.72 (SD = 1.1), 53.5% female) filled in the Big Five Inventory and measures of recycling, water conservation, electricity conservation, sustainable consumption, and sustainable transportation use based on an extended model of the Theory of Planned Behavior (TPB). TPB models were investigated in empirically derived clusters of individuals that differ by their personality traits. The results suggest that individuals in different personality clusters could be reached effectively through different means when trying to promote pro-environmental behaviors and different pro-environmental behaviors should not be regarded as homogeneous.

Individual and Environmental Predictors of Age of First Intercourse and Number of Children by Age 27

Reproductive behavior characteristics may be influenced by both social and individual factors. Recent studies have revealed that personality traits might be related to reproductive characteristics in adulthood. Little is known about potential mediators or moderators of relations between personality and reproductive behavior. The present study examines the relation between personality traits measured in early adolescence and the number of children people have by age 27, with an attempt to identify moderation and mediation effects. We used data from the longitudinal cohort (N = 585) collected as a part of the Child Development Project. Personality was measured with the use of Lanthier's Big Five Personality Questionnaire. Results from regression analyses and structural equation models showed that four of the five personality traits (except extraversion) were related to the number of children individuals had by age 27, and these associations were mediated by the age of first intercourse and participants' familial and educational plans. We also identified moderation effects of IQ and SES both on the associations of personality traits with mediators and the number of children by age 27.

People expressing olfactory and visual cues of disease are less liked

For humans, like other social animals, behaviour acts as a first line of defence against pathogens. A key component is the ability to detect subtle perceptual cues of sick conspecifics. The present study assessed the effects of endotoxin-induced olfactory and visual sickness cues on liking, as well as potential involved mechanisms. Seventy-seven participants were exposed to sick and healthy facial pictures and body odours from the same individual in a 2 × 2 factorial design while disgust-related facial electromyography (EMG) was recorded. Following exposure, participants rated their liking of the person presented. In another session, participants also answered questionnaires on perceived vulnerability to disease, disgust sensitivity and health anxiety. Lower ratings of liking were linked to both facial and body odour disease cues as main effects. Disgust, as measured by EMG, did not seem to be the mediating mechanism, but participants who perceived themselves as more prone to disgust, and as more vulnerable to disease, liked presented persons less irrespectively of their health status. Concluding, olfactory and visual sickness cues that appear already a few hours after the experimental induction of systemic inflammation have implications for human sociality and may as such be a part of a behavioural defence against disease. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

The dual evolutionary foundations of political ideology

Research over the last fifty years has suggested that political attitudes and values around the globe are shaped by two ideological dimensions, often referred to as economic and social conservatism. However, it remains unclear why this ideological structure exists. Here we highlight the striking concordance between these dual dimensions of ideology and independent convergent evidence for two key shifts in the evolution of human group living. First, humans began to cooperate more and across wider interdependent networks. Second, humans became more group-minded, conforming to social norms in culturally marked groups and punishing norm-violators. We propose that fitness trade-offs and behavioural plasticity have maintained functional variation in willingness to cooperate and conform within modern human groups, naturally giving rise to the two dimensions of political ideology. Supported by evidence from across the behavioural sciences, this evolutionary framework provides insight into the biological and cultural basis of political ideology.

Reproductive Success, Relationship Orientation, and Sexual Behavior in Heterosexuals: Relationship With Chronotype, Sleep, and Sex

Following previous studies, chronotype was related to sexual attitudes and behavior. Evening people tend to be more promiscuous and follow short-term mating strategies and extra-pair matings (EPM), which might lead to a higher reproductive success. In this study, one aim was to assess reproductive success directly by asking for children, and, second, to obtain a higher sample size for the analysis of sexual behavior and chronotype than in previous studies. N = 1,843 heterosexual persons (551 men, 1,288 women, 4 without data) responded to our online survey. Five hundred fifty-nine persons were single and 1,281 in a relationship; 203 reported having children (1.9 ± 0.81). Age was positively related and age at first intercourse was negatively related to the number of children. People being later chronotypes had fewer children, and shorter sleep duration was linked with more children. Extroversion was correlated with number of children, as was the long-term relationship orientation. Sociosexual orientation and EPM were unrelated to number of children. Age at first intercourse was earlier in evening people, and unrestricted sociosexuality was higher in late chronotypes. Morning orientation correlated with long-term relationship orientation and eveningness with short-term relationship orientation. Number of sexual partners was lower in morning people. Men were more evening oriented, later chronotypes, and slept shorter. There were no differences in sociosexual behavior, but men were less restricted in attitude and desire. Men scored higher on short-term relationship orientation and women higher on long-term relationship orientation. This study confirmed previous results about chronotype and sexual behavior but provided the first evidence that morningness was related to higher reproductive success.

Individual variation in reproductive behaviour is linked to temporal heterogeneity in predation risk

Variation in predation risk is a major driver of ecological and evolutionary change, and, in turn, of geographical variation in behaviour. While predation risk is rarely constant in natural populations, the extent to which variation in predation risk shapes individual behaviour in wild populations remains unclear. Here, we investigated individual differences in reproductive behaviour in 16 Trinidadian guppy populations and related it to the observed variation in predator biomass each population experienced. Our results show that high heterogeneity in predator biomass is linked to individual behavioural diversification. Increased within-population heterogeneity in predator biomass is also associated with behavioural polymorphism. Some individuals adjust the frequency of consensual mating behaviour in response to differences in sex ratio context, while others display constantly at elevated frequencies. This pattern is analogous to a 'live fast, die young' pace-of-life syndrome. Notably, both high and low mean differences in predator biomass led to a homogenization of individual frequency of consensual mating displays. Overall, our results demonstrate that individual behavioural variation is associated with heterogeneity in predator biomass, but not necessarily with changes in mean values of predator biomass. We suggest that heterogeneity in predator biomass is an informative predictor of adaptive responses to changes in biotic conditions.

The Myth of Optimality in Clinical Neuroscience

Clear evidence supports a dimensional view of psychiatric illness. Within this framework the expression of disorder-relevant phenotypes is often interpreted as a breakdown or departure from normal brain function. Conversely, health is reified, conceptualized as possessing a single ideal state. We challenge this concept here, arguing that there is no universally optimal profile of brain functioning. The evolutionary forces that shape our species select for a staggering diversity of human behaviors. To support our position we highlight pervasive population-level variability within large-scale functional networks and discrete circuits. We propose that, instead of examining behaviors in isolation, psychiatric illnesses can be best understood through the study of domains of functioning and associated multivariate patterns of variation across distributed brain systems.