Studies in the past have attempted to examine the ratio between the length of the index finger and the ring finger and its possible connection to certain behavioral and personality traits. A new study published in the Journal of Psychiatric Research took these notions a step further and looked at the link between the length of people's fingers and their tendency to be a diagnosed psychopath.
The ratio between index finger and ring finger length (known as the 2D:4D ratio) is believed to be influenced by the amount of testosterone and estrogen a fetus is exposed to while in the womb. The higher the testosterone in relation to estrogen, the lower the 2D:4D ratio, meaning a longer ring finger compared to the index finger.
The researchers wanted to look for the possible psychological implications of high and low 2D:4D ratios. They took scans of participants' right hands and subjected them to several psychological evaluations, including one designed to test for so-called Dark Triad personality types: narcissism, Machiavellianism, and psychopathy. In the end, they found that people who scored higher on these tests, meaning they have higher levels of psychopathic and antisocial traits, have lower 2D:4D ratios, boasting longer ring fingers than index fingers.
"We were surprised to observe such a linear association between higher symptoms of psychopathology and lower 2D:4D ratios," study author Serge Brand told PsyPost. "That is to say: 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."
The scientists noted that the study shouldn't be taken as the final word on the subject, as more work needs to be done to connect a simple physical marker to someone's psychological development. So, don't go ruling out someone after a date just because you took a close look at their hands.