Scientists from the Centre de Recherche Charles-Le Moyne in Quebec have uncovered a simple technique for identifying a psychopath.
They learned that individuals whose ring finger is extended more than their index finger may possess psychopathic traits.
The study, published in the Journal of Psychiatric Research, suggested that the harmful tendencies could be hereditary.
“While individuals with such behaviors are socially highly problematic and incur issues, such behavior might be biologically rooted and understood as a fast life history strategy,” the scientists stated.
The study sample totalled 80 people — 44 diagnosed with amphetamine use disorder (AUD), antisocial personality disorder (ASPD) or both, and 36 healthy control subjects. Researchers performed scans of participants' right hands and subjected them to psychological tests, including a test for 'Dark Triad' personality types.
Higher scores indicated increased psychopathic and antisocial traits. The results showed a correlation between those with a longer ring finger than index finger, antisocial attributes, and higher scores on Dark Triad personality tests.
Findings from earlier studies indicate that a person’s finger length is affected by the testosterone (for males) or estrogen (for females) levels that a fetus experiences in the womb. Therefore, elevated testosterone amounts imply a shorter ring finger-to-index finger ratio, whereas a longer ring finger-to-index finger ratio is caused by lower testosterone.
"The more an adult participant had signs of psychopathology, the more it appeared that this adult has been exposed to higher testosterone concentrations and lower estrogen concentrations during the prenatal period of life," Serge Brand, the lead researcher, told the press.
He cautioned that a shorter ring finger-to-index finger ratio isn’t a sure marker of psychopathy or antisocial personality characteristics.
The study revealed that men generally have a lower ring finger-to-index finger ratio than women, irrespective of psychopathic attributes. A longer ring finger than the index finger is linked to higher testosterone levels and correlates with improved sports performance.
For instance, an assessment of female Olympic athletes found significantly shorter ring finger-to-index finger ratios than the general population, and this ratio is associated with enhanced grip strength and higher jump height in footballers.