Personality and reproductive success in a high-fertility human population

Abstract

The existence of interindividual differences in personality traits poses a challenge to evolutionary thinking. Although research on the ultimate consequences of personality differences in nonhuman animals has recently undergone a surge of interest, our understanding of whether and how personality influences reproductive decisions in humans has remained limited and informed primarily by modern societies with low mortality-fertility schedules. Taking an evolutionary approach, we use data from a contemporary polygynous high-fertility human population living in rural Senegal to investigate whether personality dimensions are associated with key life-history traits in humans, i.e., quantity and quality of offspring. We show that personality dimensions predict reproductive success differently in men and women in such societies and, in women, are associated with a trade-off between offspring quantity and quality. In women, neuroticism positively predicts the number of children, both between and within polygynous families. Furthermore, within the low social class, offspring quality (i.e., child nutritional status) decreases with a woman's neuroticism, indicating a reproductive trade-off between offspring quantity and quality. Consistent with this, maximal fitness is achieved by women at an intermediate neuroticism level. In men, extraversion was found to be a strong predictor of high social class and polygyny, with extraverted men producing more offspring than their introverted counterparts. These results have implications for the consideration of alternative adaptive hypotheses in the current debate on the maintenance of personality differences and the role of individual factors in fertility patterns in contemporary humans.Big Five dimensions | life-history traits | polygyny I ndividual personality differences [also termed behavioral syndromes, temperament, or coping styles (1)] are rapidly becoming one of the most frequently studied factors underlying phenotypic variation within animal populations (2). The existence of persistent variation in personality traits poses the question of how natural selection acts on those traits and how the alternative phenotypes can coexist (3). A number of studies in nonhuman animals (>30, reviewed in ref. 4) indicate that differences in individual personality traits are associated with fitness outcomes that vary according to the individual characteristics or environments, suggesting that adaptive explanation for the interindividual variation in animal personality may be likely. In contrast, although human sciences have a long history of investigating individual personality differences from a psychological and neurobiological perspective (5), surprisingly few empirical studies have examined the ultimate causes of variation in personality dimensions in humans to date (6-9). Such knowledge, however, is critical to understanding how natural selection could shape interindividual differences in response to socioecological pressures not only from an evolutionary biological perspective but also...

The evolved psychological mechanisms of fertility motivation: hunting for causation in a sea of correlation

“…Different personality dimensions, appear to be differentially correlated with fertility [85,86]. Personality is commonly measured using the five-factor model.…”

“…Extraversion (typified by activity, sociability and dominance) positively predicts fertility [92], lifetime number of sexual partners and propensity for leaving a relationship [93] and, in Senegalese males, it also predicted polygyny [86]. Conscientiousness seems to decrease fertility, for example, in Norwegian women across 40 years of data [92] and in British panel data [94] conscientious women postponed childbearing.…”

“…It may predict more short-term mating [97] or accelerate childbirth [94], yet has been found to depress fertility altogether [96]. In Senegal [86], neurotic women had more children but, if they were low status, they had poorer quality offspring, perhaps indicating a trade-off. Personality likely acts on fertility via a number of routes, including: aiding mate retention [98]; likelihood of consistent contraceptive use [64]; and influencing subjective norms and perceived behavioural control [8].…”

“…Chasiotis et al [83] suggest that we are predisposed to parental attachment and care due to evolved mechanisms of nepotistic altruism. The importance of paternal parental care, especially father absence ( §6c), is often discussed in terms of daughter's sexual risk taking [21,53,70,86].…”

Measuring selection in human populations using the growth rate per generation

“…I have not found any studies of humans that employ a model that accounts for overlapping generations. Almost all of these studies rely solely on measures of either the quantity of reproduction such as the average children ever born [6,11], or the number of children surviving to a given age [1,5,7,12,15]. Several studies include values of the long-term growth rates [8,9,13,16,17].…”