From The Joker to Patrick Bateman, psychopaths have featured in many famous blockbuster hits throughout the years.
Now, scientists have revealed an easy way to identify a psychopath in the real world – and it’s all down to their hands.
A study has found that people who have a longer ring finger than index finger are more likely to have psychopathic tendencies.
Researchers from the Centre de Recherche Charles-Le Moyne in Quebec say the findings suggest that psychopathy may be ‘biologically rooted.’
Writing in their study, the researchers said: ‘While individuals with such behaviors are socially highly problematic and incurissues, such behavior might be biologically rooted and understood as a fast life history strategy.’
From The Joker to Patrick Bateman (pictured), psychopaths have featured in many famous blockbuster hits throughout the years
Scientists found that a low 2D:4D ratio, the ratio between your ring and index finger, has a link to psychopathy, substance addiction, and antisocial behaviour
The study, published in the Journal of Psychiatric Research, examined the hands of 80 participants – 44 who had a clinical diagnosis of amphetamine use disorder (AUD), antisocial personality disorder (ASPD) or both, and 36 healthy control subjects.
The researchers took detailed scans of the participants’ right hands and put them through several psychological evaluations, including one designed to test for Dark Triad personality types.
Higher scores on these tests indicated that the subject had higher levels of psychopathic and antisocial traits.
The results revealed a clear link between a lower 2D:4D ratio (a longer ring finger than index finger) and antisocial traits, as well as higher scores on the Dark Triad personality tests.
Researchers from the Centre de Recherche Charles-Le Moyne in Quebec say the findings suggest that psychopathy may be ‘biologically rooted’ (pictured: Heath Ledger as The Joker in The Dark Knight)
Previous studies have shown that finger length is influenced by the amount of testosterone and oestrogen a foetus is exposed to in the womb.
Higher testosterone causes a lower 2D:4D ratio, while lower testosterone causes a higher 2D:4D ratio.
Serge Brand, lead researcher on the paper, told PsyPost: ‘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.’
However, Mr Brand also stresses that a low 2D:4D ratio is not a surefire indicator of psychopathy.
He added: ‘It is important to understand that the finger lengths-ratio as a proxy of a specific exposure to prenatal sex steroids should not be understood as a person’s irrevocable fate.’
The 2D:4D ratio is not only a sign of antisocial personality traits.
Most simply, males tend to have longer ring fingers due to increased testosterone levels during development.
The results also showed that men tended to have a lower 2D:4D ratio than women, regardless of any psychopathic tendencies.
Due to the connection with testosterone levels, having a longer ring than index finger has also been associated with better performance in sports in both men and women.
For example, a study of 104 female Olympic athletes found that they had significantly lower 2D:4D ratios than members of the general public.
This has also been associated with higher scores for grip strength and even higher jump height in footballers.
HOW CAN YOU MEASURE YOUR 2D:4D RATIO?
To measure your finger straighten it and look at the palm of your hand.
At the base of your index and ring fingers there are likely to be creases. Your index finger is likely to have one crease, the ring finger is a band of creases.
Select the crease closest to the palm and choose a point on the crease midway across the base of the finger.
Mark it with a pen. Measure it from the mark to the tip of the finger.
To measure your finger straighten it and look at the palm of your hand. At the base of your index and ring fingers there are likely to be creases. Your index finger is likely to have one crease, the ring finger is a band of creases