For more than half a century, the kinds of antisocial personality traits we think of as psychopathic – such as a lack of remorse, aggression, and disregard for the wellbeing of others – have been associated with mental illness.
The line between broken and useful traits can be hazy in biology, leaving open the possibility that what is now considered a malfunction might once have been promoted by natural selection.
We might find it tricky to think of evolution benefiting antisocial people, but nature has no problem leaving room for the occasional freeloader within otherwise cooperative species like our own. Those alternative traits that make psychopaths so despised could feasibly give them an edge in a world where competition for resources is intense.
A team of Canadian researchers explored this possibility in a study published last year in the journal Evolutionary Psychology, arguing psychopathy lacks certain hallmarks of a disorder, so should be considered more like a function operating as intended.
Their conclusion is based on an analysis of existing research containing validated measures of psychopathy together with details on the person's handedness; however, this correlation echoes outdated science from the early days of criminal psychology.
Historically, links between being left-handed and a 'sinister' personality were all but given. Early models of mental illness and sociability regarded handedness as a convenient sign of an individual's degeneracy.
Science no longer regards left-handed folk as ill-fated criminals, though the question of how handedness might pair with a litany of other physiological and psychological traits remains a common one in research.
Central to it all is the age-old question of nature versus nurture. Genetics does appear to play a role in handedness, if a rather complicated one. Cultural influences may also determine how much a person favors one hand over the other, allowing them to fit into communities that favor the right-handed.
There are also a vast mix of environmental nudges, such as stress or nutrition or exposure to pollution while in the womb, that can push a person's genetic heritage for handedness into one direction or the other.
Since the researchers in this study found no clear evidence that psychopathic subjects were less likely to be right-handed, it might be assumed that their development hasn't necessarily been affected by their environment to any significant extent.
This leaves open the possibility that whatever genes are at work are operating as evolution elected, providing (as the researchers describe it) an 'alternative life history strategy' for those who inherited them.
There are plenty of reasons to hold judgement one way or another on the entire debate. Specific to this study, just 16 studies ultimately informed the conclusion, combining data on just under 2,000 individuals, making it statistically weak.
Sample sizes aside, it's hard to limit variables in studies like these, making it impossible to exclude the possibility of confounding conditions muddying the waters.
Beyond all of this, there is the more philosophical question over what makes differences in our form and function a disease in the first place. Whole books are written (one by the author of this very article) over the changing definitions of health and illness.
Psychopathy can at once be unwanted under one set of circumstances and prized in another, without invoking models of disease. It can be both an alternative strategy to survival, helping in some social contexts before becoming a disorder in another.
Like so many things in biology, disease is a convenient box we try to wrestle a complicated system into.
Psychopathy's more clinical twin, antisocial personality disorder (APD), was officially given a place in the second edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-II) in 1968. Even after a number of revisions, APD remains in the DSM, adjusted over time with criteria that can be observed and checked more objectively.
Whether we'll continue to regard psychopathy as a disorder in the future will depend on a variety of considerations, not least the results of studies like this one.
No matter how we regard disorders like APD, psychopathy can play a role in behaviors that disrupt and destroy the wellbeing of many.
Knowing more about how it works, and how to help those with it, is an answer we could all benefit from.
This research was published in Evolutionary Psychology.