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in collaboration with
Amélie Boukhobza (Clinical psychologist)
According to a forthcoming study, the difference in size between two fingers of the hand could go hand in hand with a psychiatric disorder. Is it really reliable?
Have you always thought your neighbor was a real psychopath? Look at his hands, they might tell you something. Indeed, according to a Canadian study to be published next month, people with a shorter index finger on their ring finger could present traits of psychopathy, substance use disorders or antisocial behavior. (And there you are, looking at your hands, right?)
The index/ring finger ratio studied from the angle of psychology
The difference in size between the index and ring fingers has long been studied as the 2D:4D ratio, a difference due to higher testosterone and lower estrogen exposure during the first trimester of pregnancy.
On the personality side, it has already been shown that a pronounced relationship (a shorter index finger, with a longer ring finger) is found in people with aggressive behavior and personalities belonging to the “dark triad”, i.e. narcissistic people, psychopaths and Machiavellian personalities. This relationship would also be present in mentally and athletically gifted people.
Finger size and psychopathies
This time, the study focused on the links between this 2D:4D ratio and antisocial personality disorders or amphetamine use. The scientists then compared the hands of 44 people diagnosed with one of these disorders, as well as 36 individuals in good mental health.
Analysis of the volunteers’ hands confirms that “compared to healthy controls, people with a clinically diagnosed psychiatric problem were more likely to have a shorter index and longer ring finger.”
“We were surprised to observe such a linear association between higher symptoms of psychopathology and lower 2D:4D ratios. That is, the more signs of psychopathology an adult participant had, the more they seemed that this adult had been exposed to higher concentrations of testosterone and lower concentrations of estrogen during the prenatal period of life” states the lead author of the study, Serge Brand at PsyPost magazine.
Finger size is not hard evidence
Be careful, however, not to interpret this sign in the wrong way. Although this index/ring finger ratio is present in several studies, it does not mean that the person inevitably suffers from a psychological disorder.
“It is important to understand that finger length ratio as a surrogate for specific exposure to prenatal sex steroids should not be understood as a person’s irrevocable destiny!”reassures the scientist in the pages of PsyPost.
A precaution that Amélie Boukhbza, clinical psychologist and member of our committee of experts, confirms for us:
“Even though there are studies that explore the possibility of a relationship between the 2D:4D ratio and psychotic traits, the results cannot be interpreted as definitive evidence. Psychology and psychiatry recognize that psychotic traits, Like most personality disorders, are the result of a complex interaction between genetics, environment, and life experiences. Psychotic traits are influenced by many factors, and a physical measure like the 2D:4D ratio can serve as a reliable prediction on its own.”.
In other words, it may be the consequence of exposure to particularly high prenatal testosterone, but this exposure does not necessarily translate into a psychotic disorder. We were on the verge of a misinterpretation…