The idea of a “murder gene” suggests a predetermined path to violent behavior, raising questions about whether extreme actions like murder stem from an individual’s genetic makeup. Scientifically, human behavior is complex and influenced by many factors.
The MAOA Gene
One gene discussed in relation to aggression is Monoamine Oxidase A (MAOA). This gene provides instructions for creating an enzyme that breaks down certain neurotransmitters in the brain, including serotonin, dopamine, epinephrine, and norepinephrine. These chemical messengers regulate mood, emotions, stress responses, and impulse control. Some variations of the MAOA gene, particularly low-activity forms (MAOA-L), have been studied for their association with aggressive behaviors.
A rare condition, Brunner syndrome, caused by a complete MAOA enzyme deficiency, has been linked to aggressive and violent outbursts. However, MAOA-L, the low-activity variant, is present in approximately one-third of Western populations. Research suggests that individuals with this variant might exhibit aggression, especially when provoked. Having a low-activity MAOA variant indicates a predisposition, not a guarantee, of violent behavior.
Genes and Environment Interplay
Genes engage in a complex interplay with an individual’s environment. This means that a genetic predisposition, such as the MAOA variant, can influence behavior differently depending on external factors. Environmental influences, including childhood trauma, maltreatment, or adverse social conditions, can interact with genetic factors to shape behavioral outcomes.
Studies show that individuals with the low-activity MAOA variant who experienced severe childhood maltreatment are more likely to develop antisocial behaviors. Conversely, research indicates that individuals with a high-activity MAOA variant may be less prone to antisocial behavior even after experiencing maltreatment, suggesting a protective effect. This underscores that the combination of genetic factors and specific environmental triggers is studied, moving beyond the idea of a single gene determining behavior.
Complexity of Human Behavior
Human behavior, including violence, arises from a multitude of influences. Such behaviors are considered polygenic, meaning they are affected by many different genes, each contributing a small effect. Beyond genetics, behavior is also multifactorial, shaped by a range of biological, psychological, and social elements.
No single gene or specific combination of genes has been identified that directly causes an individual to commit murder. While genes like MAOA, CDH13, DAT1, DRD2, COMT, SCL6A4, and HTR2B have been linked to traits such as aggression or impulsivity, none are deterministic. The genetic contribution to aggressive behavior is estimated to be around 50%, with environmental factors accounting for the remaining influences. Human behavior is too intricate for simple genetic determinants.
Current Scientific Understanding
The scientific community does not recognize a single “murder gene” or specific genes that directly cause violent criminal acts. While genetic factors can predispose individuals to certain temperamental traits, such as impulsivity or aggression, these traits do not equate to criminal behavior. Environmental factors are more influential in complex human actions.
The notion of a “gene of” for complex human traits oversimplifies how genetics influence behavior. Genetic evidence presented in criminal cases, particularly regarding links to violence, remains debated and is approached with caution by legal systems. There is no scientific basis to excuse or justify criminal behavior based solely on an individual’s genetic profile.