Natural Nuisance, Genetic Glitch, or Advantageous Adaptation: The Evolution of Psychopathy

In their article “Evolutionary Theory and Psychopath”, Glenn, Kurzban, and Raine (2011) examined adaptationist analysis, mutation load, and polygenic mutation-selection balance evolutionary theories in regards to psychopathy. While the group was unable to come to a definite conclusion, they did gather a wealth of information and evidence. The work also generates a number of questions: Is accidental natural selection possible? Are psychopaths more or less intelligent than the norm? Are psychopaths actually aggressive, or is it a “side effect”?

Psychopathy as an Adaptation

Psychopathy includes many notable symptoms including a lack of guilt, remorse, and concern for others, as well as superficial charm, eccentricity, grandiosity, a failure to plan for the future, and antisocial behaviour. Some research estimates psychopathy to be approximately 50% heritable, and it’s relatively stable over an individual’s lifetime. But, that’s where things start to get fuzzy. Is it merely a collection of traits? Or, is it a disorder? Does psychopathy harm the individual? Or, is it a benefit? There are excellent arguments on both sides. Perhaps, the most interesting discussions, however, are the evolutionary theories behind the phenomenon.

Adaptationist theories are based on the concept of life history strategies (LHS). These are the tradeoffs humans make due to time and energy constraints. (These tradeoffs include somatic versus reproductive effort, parental effort versus mating, quality versus quantity of offspring, and future versus present reproduction.) These choices can then be placed on a slow-fast continuum. Slow LHS include factors such as longer, quality relationships, future planning, and long-term mating. Fast LHS include multiple short-term mates, impulsive, selfishness, and reduced self-control. By these definitions, the knee-jerk reaction is to consider psychopathy a fast LHS, but that isn’t necessarily the case as some researchers argue short-term thinking and high risk taking are the only factors psychopaths have in common with fast LHS.

Balancing Selection, Mutation Load and Polygenic Mutation-Selection Balance

Glenn, Kurzban, and Raine examined two adaptationist theories. Balancing selection was the first concept, which argues psychopathy is the result of genetic variation maintained via natural selection. Theorizations behind this included environmental heterogeneity in fitness optima, which says selection favours different levels of a personality trait in different environments, and frequency dependent selection, which defines psychopathy as an infrequent genetic-based LHS driven by its rarity. Lastly, the article addressed the idea of mutation load and polygenic mutation-selection balance. This theory states that psychopathy is a collection of less harmful genetic mutations (and possibly, the result of developmental complications).

Psychopathy a Natural Accident?

While there was plenty of evidence presented for and against each of these theories, one of the arguments in favour of the mutation load theory piqued my interest. Here, researchers suggested abnormal development of the limbic system associated with psychopathy could be “a result of pleiotropic effects and are retained because the psychopathic traits they’re associated with have reproductive success” (pg. 378). What if natural selection chooses psychopathy by accident?

Years ago, research emerged discussing how evolution seems to actively select a group of genes due to their reproductive success. Unfortunately, when combined, these genes are also suspected of producing schizophrenia. Since we suspect psychopathy is 50% heritable, is it a stretch to ask if psychopathy is caused by a mix of genes evolution has selected for the other roles they play in fitness success? Combined with environmental factors, this would increase the likelihood of successful natural selection, and the various roles would work in concert with psychopathy to increase the individual’s success. If this were the case, it could provide evidence for the theories presented here.

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