Reproductive success of both males and females is linked to common personality traits, particularly neuroticism, according to a recent study published in the Proceedings of the National Academy of Sciences (PNAS).
The study, which is the first study of its kind to consider 'traditional' societies, found that in those with conventionally high birth rates, women with higher levels of neuroticism and more extravert men are likely to give birth to a larger number of children.
Scientists analysed data from 65 families in four rural villages in Senegal for the effects of personality of both partners on the number and health of their offspring using the Big Five personality dimensions (extrovertism, conscientiousness, agreeableness, openness and neuroticism). Psychologists consider these to be the five fundamental personality traits universally present in humans.
Women with above-average levels of neuroticism, prone to be anxious, depressive, and moody, had 12 per cent more children than those scoring below average. This relationship was even stronger amongst women with a higher social status.
Dr Virpi Lummaa, lead researcher on the project said that the higher sex drive among neurotic women could explain why this genetically-inherited trait occurs in larger families within developing countries, and why it has not died out during the course of evolution.
Researchers also found that women with higher neuroticism levels were more likely to have children with a decreased body mass index (BMI), reflecting malnutrition. This negative association suggests that high neuroticism carries a price for the families. There appears to be a reproductive trade-off between offspring quantity and quality.
Meanwhile men with above average levels of extraversion, prone to be sociable and outgoing, had 14 per cent more children than their introverted counterparts.
Dr Lummaa said: 'Our results show that personality predicts family size differently in men and women, and those men with largest families have personality aspects different from the women with the largest families. Gaining understanding of such individual-level determinants of reproductive decisions helps in the current debate on the role of individual versus social factors in explaining recent fertility changes around the world'.
Former work in this field has involved modern Western populations. This research on more traditional people enabled the team to examine how personality affects fertility rates in a 'natural environment' as characterised by high birth rates, akin to an evolutionary approach.
The research was conducted by Dr Virpi Lummaa from the University of Sheffield, Dr Alexandra Alvergne from University College London, and Markus Jokela from the University of Helsinki.