Violence and Heredity
Violence has been part of every civilization with violence, in primitive civilizations being necessary for survival. Due to the survival advantage of aggression, violent traits were successfully passed down through the process of natural selection. Due to advances in gene studies, today, violence is regarded as non-pathological; a normal behavioral pattern. Violence according to the WHO (World Health Organization) is defined as the deliberate utilization of physical power or force whether directly or indirectly against an individual, community, or state that culminates in or increases the chances of physical or psychological injury, deprivation, or death.
Aggression and antisocial behavior is a complex phenomenon associated with multiple genes and environmental variables. Mendlewicz, (1998) notes that complex behaviors such as those dictating personalities are controlled by multiple genes. Therefore it is hypothesized that a spectrum of genetic risk regarding the dimensions of behavior is responsible for the normal to severe dysfunctional behavior. The complexity is further complicated by the existence of ethnic differences in the pertinent genes, phenocopies, polygenicity, and incomplete penetrance since they hinder genotype-phenotype correlations.
One hypothesis states that polymorphisms and mutations of genes that were originally evolved to enhance survival in states of hunger and starvation, together with several environmental influences incline an individual to antisocial and aggressive behavior. Among the characteristic features of antisocial personality disorder is familial history of the disorder and early onset of antisocial behavior. There is a scientific consensus on the link between aggressive and criminal behavior and defective neural networks in the temporal and frontal lobes causing altered emotional and behavioral responses concerning morality. The responses are attributed to the expression of several relevant genes on exposure to stress.
Metabolic and genetic studies of a large Dutch family with a syndrome of antisocial behavior and borderline intellectual disabilities such as rape attempts, arson, and aggression among males revealed a defect in the p11-12 region of the X chromosome. This was a point mutation in the MAOA (monoamine oxidase A) gene 8th exon whose role is the formation of a terminal codon from glutamine. The MAOA enzyme has a role in the cerebral neurotransmitter metabolism for norepinephrine, epinephrine, and serotonin. Studies reveal that MAOA deficiency in adults results in abnormally elevated concentrations of norepinephrine and structural changes in the somatosensory cortex which manifested as aggression in males.
Empirical evidence suggests the role of serotonin in the control of violent impulses: serotonin has a role in the inhibition of impulsive habits. Depending on the various genotype and the additional influence of environmental forces, the expression of antisocial behavior ranges from minor personality disorders to major psychiatric disorders such as chronic gambling, blatant violent behavior, and suicidal ideation. Molecular studies of various genes have established that polymorphisms in genes encoding for particular serotonin transmission proteins are linked to violent-antisocial behavior.
Environmental factors can also explain the association between heredity and violence. Maltreatment during childhood is a global risk factor for aggressive and antisocial behavior: there is a 50% higher risk of criminal behavior among adults exposed to childhood maltreatment. Despite this fact majority of the children who are mistreated do not turn out to be delinquents or criminals. The only explanation for this differential response to childhood maltreatment is susceptibility conferred by an individual’s genotype. Genetic studies determined that a VNTR (variable number tandem repeat) polymorphism in the MAOA promoter area determined the genetic susceptibility to the development of antisocial and violent behavior with exposure to childhood maltreatment.