What makes a criminal? (Biological)

Genetic Factors

Twin and adoption studies suggest a genetic predisposition to criminal behaviour, with concordance rates higher for monozygotic (identical) twins than dizygotic (non-identical) twins.
Candidate genes, such as the Monoamine Oxidase A (MAOA), have been implicated in aggressive criminal behaviour. This ‘warrior gene’ influences the breaking down of neurotransmitters and is linked with impulsivity.
Epigenetic factors can produce changes in gene expression. These changes, provoked by environmental triggers, may facilitate criminal behaviour in genetically susceptible individuals.

Neurophysiological Factors

The prefrontal cortex, responsible for decision-making and impulse control, has been found to be smaller and less active in criminals, particularly in antisocial and psychopathic individuals.
Abnormalities in neurotransmitters may contribute to criminal behaviour. Low levels of serotonin and high dopamine levels have been implicated in impulsivity and aggressive behaviour.
Brain injuries, neurodevelopmental disorders, or diseases that affect the brain (such as dementia) can induce criminal behaviour due to neurological changes.

Biochemical Factors

Hormonal imbalances have been shown to affect behaviour and mood. Elevated levels of testosterone are often found in violent criminals.
Poor diet and nutrition can lead to deficiencies in essential nutrients affecting brain function, leading to behaviour problems. A lack of omega-3 fatty acid, for example, has been linked to behavioural issues.
Substance abuse and addiction can lead to criminal activity directly, or indirectly through effects on neural and physiological systems. Alcohol and drugs can alter the brain’s structure, damaging areas involved in decision-making, impulse control, and judgement.

Remember to consider that these factors should not be seen as direct causal links to criminality. They merely increase one’s vulnerability towards criminal behaviour. Many individuals with these genetic, neurophysiological, or biochemical factors do not engage in criminal behaviour. This area of study emphasises the interplay between biology and environment (nature and nurture), showing how these biological factors are often influenced and triggered by environmental conditions.