Dark Triad personality traits, second-to-forth digit ratio (2D:4D) and circulating testosterone and cortisol levels

Introduction: Dark Triad (DT) personality traits (psychopathy, Machiavellianism, and narcissism) show sex differences and associations with hormones. Understanding aetiology may assist in mitigating the harm of these potentially adverse characteristics. Low second-to-fourth digit ratio (2D:4D) is hypothesised to be a marker of high prenatal testosterone exposure and may provide important information about organisational hormones. The aim of the present study was to measure Dark Triad and Big 5 personality traits in relation to digit ratio, salivary testosterone, and cortisol. Methods: A non-clinical sample (N = 268; 49.25% Female, age M25.20 ± 8.77 yrs) completed the Short Dark Triad and International Personality Inventory Pool - Mini. Afternoon saliva was analysed for testosterone and cortisol, and 2D:4D finger ratios were measured. Results: Males scored higher on DT traits than females. Females scored higher on Big 5 agreeableness and neuroticism. Males had higher testosterone and cortisol levels and lower 2D:4D than females. Digit ratio correlated inversely with salivary testosterone, Machiavellianism, and psychopathy. Testosterone levels correlated positively with cortisol levels and psychopathy and negatively with agreeableness, neuroticism, and Machiavellianism. Conclusions: These results provide indications that Machiavellianism and psychopathy (Dark Triad) traits, but not narcissism or Big 5 traits, are linked to markers of prenatal testosterone exposure. Results also replicate sex differences seen in 2D:4D digit ratios, with males having a shorter second-relative-to-forth finger. Links between circulating testosterone, digit ratios, cortisol and personality traits provide further information about potential biological bases of personality