Psychopathy is characterized by “antisocial, impulsive, manipulative, and callous behavior.” Many of its defining characteristics currently fall under the diagnostic criteria for Antisocial Personality Disorder in the DSM-5. Despite the widespread belief among the scientific community that psychopathy is a mental disorder, researchers have proposed an alternative, evolutionary-minded perspective: that psychopathy is, instead, a strategy of social exploitation of maintained life history. by frequency-dependent negative selection.
The evolutionary view of psychopathy postulates that “the risky, opportunistic, and callous behavior” characteristic of psychopaths would have increased reproductive success in ancestral environments. These traits would have emerged when they were needed to promote physical fitness. For example, under conditions of a high ratio of cooperators to psychopathic individuals, psychopathic individuals might exploit the trust and cooperation of others to improve their reproductive opportunities. Psychopathic traits under such conditions would have been favored by selection.
One testable hypothesis regarding this debate is the extent to which psychopathic (vs. non-psychopathic) individuals show signs of neurodevelopmental disturbances. An indirect measure of such disturbances is laterality (left-handed/right-handed/ambidextrous), since not being right-handed indicates neurological development problems.
A recent meta-analysis, involving more than 2 million people, found that approximately 11% of the population was left-handed. The right-handed bias is thought to come from selection pressures throughout our evolutionary history. There are both structural and functional asymmetries in the human body, and brain lateralization (i.e., neural functions are more dominant in different hemispheres of the brain) is one of those asymmetries. Since the left hemisphere of the brain controls the right side of the body, right-hand dominance may be a byproduct of the genetically determined functional asymmetry of brain lateralization for left hemisphere language processing and/or fine motor skills. .
For another meta-analysis, researchers focused on laterality as an indicator of neurodevelopmental disturbances (Pullman et al., 2021). Not being right-handed has been associated with low birth weight, birth complications, prenatal stress, and prenatal hormone exposure, suggesting that it may be associated with disruption of pre- and perinatal brain development of critical brain structures. For example, compared to healthy control groups, people with schizophrenia and depression are more likely to be left-handed.
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This meta-analysis only included studies that: were conducted in English, included an identifiable sample of mostly adult participants, had at least 10 participants in each group, used a validated measure of psychopathy (but not antisocial personality disorder), measured laterality and contained sufficient statistical information for effect size calculation. Additionally, non-right-handedness was defined as left-handedness, mixed handedness, or ambidexterity, measured with self-reported hand preference, writing hand preference, or validated hand inventories.” The meta-analysis included 16 studies from 25 individual reports published between 1985 and 2017, with an overall total of 1818 participants.
What did you find
- Pullman and colleagues found no support for the mental disorder model of psychopathy, and the meta-analysis provided partial support for the adaptive life history model of psychopathy.
- There was no difference in the rate of non-right-handedness among community participants scoring high (vs. low) on psychopathy. And although there was no difference in rates of right-handedness among psychopathic (vs. non-psychopathic) offenders, there was a trend for those with higher scores on the interpersonal/affective dimension of psychopathy to have lower rates of right-handedness, while that those with higher scores on the behavioral dimension had higher rates of non-right-handedness. The behavioral dimension of psychopathy may be conceptually more similar to antisocial personality disorder and lifelong persistent delinquency.
- Finally, there were no differences in rates of non-handedness between psychopathic (vs. non-psychopathic) mental health patients.
The authors point out several limitations. There were a small number of primary studies that examined the relationship between psychopathy and handedness; as such, low statistical power could preclude the discovery of any group differences that exist. Additionally, the authors were unable to address the confounding variable of comorbidity with psychopathy; It is possible that psychopathic individuals have other mental illnesses (not determined in this work), which could confound the results. Interestingly, the comorbidity rate of mental illness with psychopathy tends to be lower than that of other mental disorders, which is consistent with the adaptation perspective. Finally, the included samples were partially or completely composed of women; However, the adaptive model of psychopathy pertains to men and may not extend to women. Therefore, future work should examine the relationship between psychopathy and handedness in men specifically.
Bibliographic reference: Pullman, LE, Refaie, N., Lalumière, ML, & Krupp, DB (2021). Is Psychopathy a Mental Disorder or an Adaptation? Evidence From a Meta-Analysis of the Association Between Psychopathy and Handedness. In Evolutionary Psychology (Vol. 19, Issue 4, p. 147470492110404). https://doi.org/
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