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.

Fig. 1.

Neuroticism is associated with an increased number of children in women. The figure shows the number of children controlled for age and rank (residuals) against scores of neuroticism (n = 74).

Fig. 2.

Women's neuroticism is associated with a reduction in the child's physical condition at ages 0–5 y in low but not in high social classes. (A) Mean child BMI and low social class (n mothers = 41). (B) Mean child BMI and high social class (n mothers = 33). For similar relationship between women's neuroticism and mean child MUAC, see Fig. S1.

Fig. 3.

The ultimate reproductive success in women is maximized for intermediate levels of neuroticism. For each woman, the ultimate reproductive success corresponds to her number of children times the mean chance of survival of her children to age 5 given their body mass index (n mothers = 74). See SI Materials and Methods and Fig. S2 for details.

Fig. 4.

Extraversion is positively related to fitness related traits in men. (A) Social class. (B) Marital status (C) Number of children controlled for age (residuals) (n = 62). Raw data are indicated by sunflower symbols in A and B, and by dots in C. Solid lines show predicted relationships between extraversion and reproductive success variables and dashed lines represent the 95% CI around the predicted slope.