An international team of scientists from Canada, Iran, Switzerland and the United Kingdom found a link between the ratio of the length of the index and ring fingers and symptoms of several psychopathological personality traits, including antisocial behavior and substance abuse. The study was published in the scientific journal magazine Journal of Psychiatric Research (JPR).
Previous research has shown that the length ratio of the index finger (2D) to the ring finger (4D), commonly known as the 2D:4D ratio, can be an indicator of various behavioral and personality traits. This ratio is believed to be affected by the levels of testosterone and estrogen to which the fetus is exposed in the womb.
The higher the testosterone level relative to estrogen, the lower the 2D:4D ratio; this often results in a longer ring finger compared to the index finger.
Researchers set out to deepen their understanding of how finger length ratio is associated with certain mental disorders and personality traits. The study focused on individuals with amphetamine dependence (AUD), antisocial personality disorder (ASPD), and a combination of both diagnoses (AUD + ASPD).
The researchers recruited 80 participants divided into two main groups: 44 individuals with a clinical diagnosis (25 with AUD, 10 with ASPD, and nine with AUD+ASPD) and 36 healthy controls. Volunteers were subjected to various tests to determine their personality parameters and mental state.
The researchers found that participants in the clinical group had a significantly lower 2D:4D ratio than the healthy control group. This indicates that the ring finger tends to be longer than the index finger in people with AUD, ASPD, and especially in people with both conditions. Additionally, men in the groups had a lower 2D:4D ratio than women.
“We were surprised by this direct relationship between higher symptoms of psychopathology and lower 2D:4D ratios. That is, the more psychopathology a participant had, the more likely that person was exposed to higher concentrations of testosterone and lower concentrations of estrogen in prenatal life.” ” said study author Dr. Serge Brand.
Scientists emphasized that this factor does not determine the future fate of a person, but only indicates a tendency towards certain behavior, which will not necessarily be associated with antisocial behavior or drugs. For example, among Swedish Olympic team athletes, there are many women with a low 2D:4D ratio, indicating that they were exposed to high levels of testosterone before birth.
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