New research suggests that prenatal exposure to different levels of testosterone and estrogen, as estimated through 2D:4D finger length ratios, is linked to narcissistic traits in adulthood. The study, published in the journal Personality and Individual Differences, highlights a potential biological basis for gender differences in narcissism. The 2D:4D ratio refers to the comparative lengths of the index finger (second digit) and the ring finger (fourth digit). This ratio is considered a marker of prenatal hormone exposure, with lower ratios indicating higher prenatal testosterone levels and h…