Since I began studying psychopathy, I have often wondered about an evolutionary basis for this dangerous disorder. Psychopathy is considered to be a developmental disorder (Blair, 2006), which means that through its normal course of development the brain experiences stresses or biochemical changes that are not conducive to proper neurological development. This idea is supported by suppositions from both behavioral psychology and neuroscience; firstly, in behavioral psychology, it is suspected that serious child abuse could be an underlying factor behind psychopathy (Kunitz et al., 1998), and secondly, in neuroscience, it has been noted that many with psychopathy show a significant underdevelopment of a number of regions in their brain (for a review see Pemment, 2012).
The environment of an organism is crucial in evolution because it is the selecting factor behind which genes get passed to the next generation. For example, if the genes are creating organismal structures that imbue an advantage in the particular environment, then the organism gets to reproduce and pass on these genes. Or perhaps the genes promote a particular kind of behavior within this environment that promotes its reproductive success, again, allowing it to pass on its genes. If we work with the assumption that child abuse and trauma could be behind the development of psychopathy, we have the environment in question, only it is more than a selecting factor – it is a causal factor.
Clearly, though, not all children who suffer through abuses and trauma become psychopathic, and this could be due to a genetic component. If a child has certain alleles (variations of a particular gene), then the impact of the environment could be either enhanced or diminished. We know that variations of the gene for monoamine oxidase (MAO) have long been implicated in violent behavior (Schalling et al., 1998). MAO is an enzyme that breaks down monoamines, such as serotonin and other neurotransmitters. Alleles for SNAP proteins have also been implicated in psychopathy (Basoglu, 2011). SNAP proteins are involved in the docking of synaptic vesicles during neurotransmission.
Is it possible that an environment of trauma and abuse could have anything to do with these implicated genes? A stressful environment could, in theory, alter the transcription rate by altering the tagging on the promoter regions of certain genes; this phenomenon is known as epigenetics, whereby changes in the immediate environment of the DNA (caused by social interactions, diet, and other interactions) modify mRNA molecules and histone groups. Both of these can change the transcription rate of the mRNA and potentially the translation rate of DNA. The end result would mean a higher or lower number of certain proteins, such as MAO or SNAP, and this could result in psychopathic traits. On top of this, rogue alleles for MAO or SNAP could produce rogue protein structures, meaning that not only the number of these proteins but the structural uniqueness of the protein could be involved. The amount of the protein would be influenced by the stressful or traumatic environment, but the structural uniqueness would not.
It has been shown in rodents that stress is not conducive to neurogenesis (Dranovsky & Hen, 2006), and this could be why that in the psychopath brain we see a lack of gray matter in the frontal lobe and amygdalar abnormalities (Pemment, 2012). Nobody has successfully “connected” the neuronal abnormalities in psychopathy to the actual behavior exhibited by these individuals, but it is not hard to speculate, especially as the interactions between the amygdala and frontal lobe are involved with fear processing and morality. But do these abnormalities have anything to do with the expression of the alleles mentioned above? It could be that trauma and abuse effect the expression of MAO and SNAP, and effect neuronal developmental, but the expression of MAO and SNAP are not related to development.
So back to the question of evolution, we need to look at inheritance. Children will inherit the genes for MAO and SNAP from their parents, and the expression of any rogue alleles becomes a simple case of genetic crosses (homozygous dominant, heterozygous, and homozygous recessive). If psychopathy is “located” here, then there will be varying odds that it will be expressed and the person could manifest as a psychopath. This alone, however, is unlikely to explain the neuronal mal-development seen in psychopaths.
In a perverse kind of way, psychopaths could inherit the environment of their parents. If a psychopathic parent was subjected to child abuse and trauma, then perhaps they will act violently and aggressive to their children because of their disorder – violence begets violence. The children of these individuals will not only have their genes, but will be subject to similar environmental stressors that their parent(s) suffered. Conducive environment plus genetic susceptibility increases the likelihood of a psychopathic child.
I would like to posit that there is an aspect of cultural evolution here in the continued appearance of psychopaths, or at least of violent individuals. Throughout history it has not been uncommon for families to keep up the same profession. Therefore, if a brutal father expected a son to follow in his footsteps, the son would be exposed to the father’s profession, which if a violent profession, such as a soldier, assassin, guard, or fighter, could expose the child to the kinds of tragedy responsible for stymieing neuronal development. The world of the father would become the blueprint for the future world of the child. This would promote the succession of a culture throughout the ages, especially if it was socially accepted, which violence usually is in some contexts.
In Pinker’s The better angels of our nature: Why Violence has declined, he argues that violence has declined over the course of human history. Today it is estimated that those with Antisocial Personality Disorder (APD) number about 1% of the population (the extreme of whom are psychopathic). Perhaps 300 years ago this number was much higher? If a violent culture acts as a genetic switch, then a decline of violence can only help reduce the psychopathic among us.
Copyright Jack Pemment, 2013
Basoglu, C.; Oner, O.; Ates, A.; Algul, A.; Bez, Y.; Cetin, M.; Herken, H.; Erdal, M.E.; Munir, K.M. (2011) Synaptosomal-associated protein 25 gene polymorphisms and antisocial personality disorder: Association with temperament and psychopathology, Canadian Journal of Psychiatry, 56 (6), 341-347
Blair, R.J.R. (2006) The emergence of psychopathy: Implications for the neuropsychological approach to developmental disorders, Cognition, 101, 414-442
Dranovsky, A.; Hen, R. (2006) Hippocampal neurogenesis: Regulation by stress and antidepressants, Biological psychiatry, 59, 1136-1143
Pemment, J. (2012) The neurobiology of antisocial personality disorder: The quest for rehabilitation and treatment, Aggression and violent behavior, (In press)
Pinker, S. (2010) The better angels of our nature: Why violence has declined, Penguin Books, New York
Schalling, D.; Edman, G.; Asberg, M.; Oreland, L. (1988) Platelet MAO activity associated with impulsivity and aggressivity, Personality and individual differences, 9(3), 597-605