Can Evolutionary Psychology Explain Psychopathy?

In the last issue I reported on the fairly new field of Evolutionary Psychology. Essentially, evolutionary psychology says that human thoughts, feelings and behaviours were produced by natural selection. For us in the Research Department, the most interesting applications of evolutionary psychology have to do with the ways it can explain criminal (and especially) violent behaviour.

For example, two psychologists from McMaster University -- Martin Daly and Margo Wilson -- have studied murder. They showed that most murder victims are known to their murderers but are not biologically related to them. They hypothesized that there is an evolved mechanism that inhibits people from acting violently towards their close kin. That is, back in the ancestral environment, genes that prevented people from harming their biological relatives would have been more successfully reproduced (compared to genes that led to harming relatives) in succeeding generations. And, therefore, people who had such genes would have more descendants around today. Thus, according to the theory, people should be much more likely to murder relatives by marriage (including spouses) and step-relations than biological kin. And this is exactly what Daly and Wilson found.

Daly and Wilson also noted that this is something we are all implicitly aware of; people who kill their blood relations are much more likely to be found insane than those who kill their in-laws. Daly and Wilson argue that, all other factors being equal, we find killing blood kin to be much more deranged, irrational and less understandable than killing other relatives, even though we might not be explicitly conscious of this attitude.

By this account, it would seem that the least likely kind of murder would be a mother murdering her own children. Women are much less likely to commit murder than men, but when women do murder, their own children are frequent victims. From an evolutionary account, how could this ever be advantageous. That is, were there ever circumstances in our ancestors' environment when a mother's reproductive success would be enhanced by killing her own children? Animal mothers kill (and eat) their own offspring when food supplies are short and when there is a lot of crowding -- circumstances where the offsprings' survival prospects are poor and where the mother's reproductive success is better if she conserves her resources and delays rearing offspring until later. Similarly, Daly and Wilson showed that a human mother is most likely to kill her children when she is young (has lots of opportunity to have more children), the children are small (have not already received a large maternal investment), the mother is alone (the father and his material investment is absent), and if the mother has the opportunity to marry a man who does not want to raise another man's children.

Of course, these processes can and probably do occur quite unconsciously. And saying that such behaviour is understandable from an evolutionary perspective does not mean that it is acceptable or morally appropriate.

One of our interests in evolutionary psychology pertains to psychopathy. Our theory is that psychopathy is not a disorder. A disorder, by definition, is the failure of some physical or mental feature to perform its natural (evolved) function. Thus, schizophrenia is a disorder because it prevents the brain from performing the thinking evolution designed it to do. On the other hand, we speculate that evolution designed a subspecies of humans who use deception and cheating to get resources from others but do not reciprocate. The key characteristics of such a subspecies ought to be: skill at deception, lack of concern for the suffering of others, ease and flexibility in the exploitation of others, extreme reluctance to be responsible for others (including, in the case of males, their own offspring), and total lack of real concern for the opinion of others. These are psychopathic traits. The point here is that psychopathy is not a disorder because psychopaths (and their mental characteristics) are performing exactly as they were designed by natural selection. According to this view, psychopathy is an adaptation.

Research with other species and with mathematical models shows that it can be reproductively advantageous to be a dishonest cheater when cheaters are in the minority and when it's possible to move around so that a cheater's reputation is not known to everyone. There are two possible ways psychopathic behaviour could arise: everyone is potentially a psychopath and will become one if conditions are ripe, or psychopaths are a distinct subspecies who adopt a genetically-determined life-long strategy.

Our theory is that, although nonpsychopaths are capable of some criminal behaviour under the right (wrong) circumstances, psychopaths form a distinct subgroup of humans who use distinct life-long deception reproductive strategies under all circumstances.

There aren't many data yet to directly support our theory. We have shown that, as adults, psychopaths form a distinct subgroup qualitatively different from other offenders. There is evidence that criminal behaviour, childhood conduct disorder (a precursor of psychopathy) and adult antisocial personality disorder (related to psychopathy) all have inherited components. However, little is known about the heritability of psychopathy itself.

Studies of the psychophysiology of psychopaths indicate fundamental differences in the ways psychopaths process information (especially emotionally powerful information), and learn from experience (they are especially resistant to the effects of punishment). These have been thought of as defects, but it's just as possible that they are adaptations that facilitate a life-long cheating, deceiving and manipulating strategy.

A strategy that, as long as the psychopath keeps moving around to find new victims, and as long as there aren't too many psychopaths about, will ensure (or, more importantly, in the ancestral environment, would have ensured) a high degree of reproductive success.

Much more research is needed, however. Interesting unresolved questions are: What is the heritability of psychopathy? What genes underlie psychopathy? What environmental influences affect the expression of psychopathy? And what interventions undertaken by the rest of us (the nonpsychopaths) can reduce or eliminate the expression of psychopathy. Together with our colleagues at Queen's University, we are tackling some of these questions.