New research has found an association between certain personality traits and Darwinian fitness. The preliminary research, published in Personality and Individual Differences, suggests that personality influences the number of offspring a person has.

“There is a large debate in evolutionary social sciences regarding the biological adaptiveness of behavior in contemporary human populations. The dispute is perhaps the hottest in the field of personality,” said study author Janko Međedović of the Institute of Criminological and Sociological Research in Belgrade.

“This is why empirical research that explores the relationship between personality and fitness (measured by reproductive success, longevity, parental investment, etc) is of high importance. Previous research in this field have been focused on a Big Five model of personality. We decided to investigate another prominent model of personality structure, the HEXACO personality framework.”

HEXACO is an acronym for the names of the six personality factors: Honesty/Humility, Emotionality, Extraversion, Agreeableness, Conscientiousness and Openness to Experience.

The study of 255 Serbian individuals over the age of 50 found that three of these factors were associated with short-term reproductive success. Openness to Experience and Honesty-Humility were negatively correlated with the number of children the participants had, while Emotionality was positively correlated.

In other words, individuals who are more conventional, more boastful, and more sensitive tended to also have more offspring.

“The findings are largely in accordance with previous studies: personality traits are related to fitness, they participate in fitness optimization and life-history pathways,” Međedović told PsyPost. “The data corroborate the conceptual views of human behavioral ecologists who claim that, despite the potential adaptation-environment mismatch in contemporary populations, human behavior is in fact largely adaptive.”

The researchers also found that low Openness and high Conscientiousness predicted a higher number of grandchildren, while more Extraverted individuals tended to reproduce earlier in their lifetime.

“Personality traits help us solve important biological challenges such is having children, raising them, choosing the timing of reproduction, etc. Since they are heritable traits, this suggests that they are probably under current natural selection. Hence, they are continuing to evolve with other human characteristics and participate in our phylogeny,” Međedović said.

The study, like all research, has limitations. Međedović warned about drawing any broad conclusions from the findings.

“Generalizability of findings is a problem in all psychological research. However, the problem is even more pronounced if you try to make evolutionary-relevant conclusions from the study,” Međedović explained.

“The ideal sample would be population-representative group of individuals in a post-reproductive phase of life. We tried to make our sample as heterogeneous as we could, but it is still very likely that our findings are constrained by various sample characteristics. Secondly, in a cross-sectional design causality cannot be undoubtedly established. The ideal design would incorporate longitudinal studies where we could measure personality in young adults and measure fitness in the same individuals a couple of decades afterwards.”

“Exploring the relationship between personality and fitness is scientifically important per se; however it is only the starting point of examining personality in behavioral ecological framework,” Međedović added.

“One of the main topics here is to explain the variation in personality traits. Why are some individuals more aggressive than others? Are there evolutionary forces which maintain this variation? Behavioral ecologists have already developed several heuristically powerful models to explain the variation of personality traits in animals. Our task now is to see are these models applicable to humans, to what extent, and under what constraints. Answering to this question will help us to understand the key problem of human individuality: why is there personality in the first place?”

The study, “Revealing complex relations between personality and fitness: HEXACO personality traits, life-time reproductive success and the age at first birth“, was authored by Janko Međedović, Mina Šoljaga, Ana Stojković, and Ivana Gojević.