New research provides evidence that some aspects of the Dark Triad of personality are linked to markers of prenatal testosterone exposure. The findings, published in Biological Psychology, shed light on the relationship between biological processes and personality development.
The Dark Triad refers to a set of three personality traits: Machiavellianism, narcissism, and psychopathy. Individuals high in Machiavellianism are manipulative and strategic in their interactions, while those high in narcissism exhibit an excessive sense of self-importance and a need for admiration. Psychopathy is characterized by impulsivity and a lack of remorse.
It has been consistently observed that men tend to score higher than women on Dark Triad characteristics. However, the extent to which these sex differences are due to biological factors, such as sex hormones, is still unclear. The authors behind the new study sought to help fill this gap in the research literature.
Testosterone, the primary male sex hormone, plays a crucial role in regulating sex differentiation, reproductive tissues, and secondary sex characteristics. It is produced in the testes in males and to a lesser extent in the ovaries in females, as well as in the adrenal glands and hypothalamus in both sexes. The hypothalamic-pituitary-gonadal (HPG) axis controls the release of testosterone and other gonadal steroids.
Research has shown that testosterone is linked to social status-seeking, dominance, and aggression. However, there are limited studies on the relationship between testosterone and the Dark Triad, with only a few studies suggesting a potential relationship between testosterone and narcissism in males.
“The Dark Triad traits are very misunderstood – even by those in the field of psychology,” said study author Alexandra South, a PhD candidate at the University of Wollongong.
“I am interested in deconstructing these personalities which have so many assumptions surrounding them, and finding out how to better understand them, how they function, interact with others, and shape behaviors, with the ultimate goal of fostering empathy, productive dialogues, and more effective interventions within both clinical and everyday settings.”
To conduct their study, the researchers recruited 268 participants (132 females and 136 males) aged between 18 and 65 years. The sample consisted of both students and individuals from the general population.
The Dark Triad personality traits were measured using The Short Dark Triad, a 27-item scale that assesses Machiavellianism, narcissism, and psychopathy. The Big Five personality traits were assessed using the International Personality Inventory Pool – Mini, a short-form version of a measure based on the Five-Factor Model. Salivary samples were collected to measure testosterone and cortisol levels.
The participants also provided handprints for calculating 2D:4D digit ratios. The 2D:4D digit ratio is a measure that compares the lengths of the index finger (2D) and the ring finger (4D) on the hand. It is calculated by dividing the length of the index finger by the length of the ring finger. This ratio is believed to be influenced by prenatal hormone exposure, particularly testosterone.
“Your finger length might give you an idea of how much testosterone you got in the womb,” South explained. “On average, males have a lower 2D:4D ratio than females, which means, their index fingers tend to be shorter compared to their ring fingers (compared to those of females), which may indicate higher testosterone before you were born.”
The results of the study showed several differences between male and female participants in terms of hormone levels and personality traits. Men had higher levels of testosterone and cortisol compared to women, and they also scored higher on all Dark Triad traits. On the other hand, women had higher levels of agreeableness and neuroticism than men.
The study also found correlations between hormone levels and personality traits. Testosterone levels were higher in people who displayed heightened psychopathy, Machiavellianism, and imagination. In both men and women, higher testosterone levels were associated with being less agreeable and more emotionally unstable.
In addition, a lower 2D:4D digit ratio (indicating higher prenatal testosterone exposure) was associated with higher testosterone levels and higher scores on Machiavellianism and psychopathy. This was true for both men and women. However, no significant link was found between digit ratio and narcissism in this sample.
The findings suggest “that even before we’re born, our personalities are already taking shape,” South told PsyPost. “Specifically, traits linked to psychopathy and Machiavellianism might start forming in the womb, shaped by factors like testosterone levels. This doesn’t just help us understand ourselves better, but also gives us new ways to manage these traits if they become a problem.”
The findings also have implications for understanding personality and its relationship to sex and hormones.
“The huge importance of sex differences in these relationships was particularly interesting to me,” South said. “We really don’t know everything about the Dark Triad yet – sure, males score higher, but why is this? Hormones, while a factor, don’t seem to tell the whole story, so what else is going on here? I hope to look into this with future research.”
This study has a few limitations that need to be considered. Firstly, it is a cross-sectional study, meaning it was conducted at a specific point in time and cannot show causality. The study was also done with a non-clinical group of participants under normal conditions, so it may not capture hormonal variations that can occur throughout the day or due to stress.
“Who we are and where our stories come from starts before we even have a say in the matter – so have some compassion for yourself and those around you,” South added.
The study, “Dark Triad personality traits, second-to-forth digit ratio (2D:4D) and circulating testosterone and cortisol levels“, was authored by Alexandra J. South, Emma Barkus, Emma E. Walter, Carley Mendonca, and Susan J. Thomas.
