Brain Injuries and Biochemical Factors
Sometimes brain damage directly causes criminal behaviour. Phineas Gage's famous case perfectly illustrates this - after a metal pole pierced his skull, destroying his frontal lobes, his personality completely changed from friendly to aggressive and inappropriate.
Gage's case supported localisation theory - that different brain parts control specific functions. Damage to frontal lobes particularly affects impulse control, risk assessment, and rule compliance. Prisoners statistically have higher rates of brain injury than the general population.
However, brain-injury-related crimes remain rare, and prisoners' injuries might result from their criminal lifestyle (fights, accidents) rather than cause it.
Biochemical factors also influence behaviour. Testosterone peaks coincide with highest male crime rates, and it's linked to violent offences. Ellis and Coontz demonstrated this age-related pattern clearly.
Female hormones affect behaviour too - premenstrual tension, postnatal depression, and lactation are accepted as partial legal defences for crimes like shoplifting and infanticide, recognising their impact on mood and judgement.
Substance abuse triggers criminal behaviour through disinhibition. Saunders found alcohol involved in 1000 daily arrests, whilst Flanzer reported it in 80% of US family violence cases.
Real-World Application: Courts increasingly recognise biological factors in sentencing, balancing personal responsibility with medical understanding.
These biological influences are significant but usually require environmental triggers to produce criminal behaviour.