Several factors seem to predispose individuals to violence in later life: Birth complications A study of 4,269 live male births concluded that children who had complications that led to some sort of brain impairment were likely to become violent in later life. Genetics Specific genes raise the odds of a person becoming aggressive. When the gene for the enzyme monoamine oxidase A is lacking, it affects the functioning of the brain. People with low levels of the enzyme who suffer child abuse show antisocial behaviour in later life. Low physiological arousal Studies have shown that low mental arousal at the age of 15 means crime can be predicted at 24 with an accuracy of 74 per cent. Experts believe subjects may seek stimulation through crime to raise arousal levels. A low arousal and low heart rate also indicate a lack of fear. Bomb disposal experts typically have lower heart rates than the average person. Cortex impairment People with damage to the frontal part of the brain are more likely to become violent and aggressive. Scans of 41 murderers in California showed normal brain activation in the back but the functioning of the front part (which controls behaviour) was significantly reduced. Malnutrition A study in Mauritius showed that children with poor nutrition were more antisocial as it led to poorer brain functioning and lower IQ. Better nutrition, physical exercise and cognitive stimulation from age 3 to 5 led to a significant reduction in conduct disorder and hyperactivity at 17, and a much lower crime rate. An English study where prisoners were given fish oil (which contains a lot of omega-3 fatty acids) showed a reduction in aggressive behaviour. Omega-3 helps the brain to function efficiently. Smoking and drinking during pregnancy Lead to a higher rate of violent criminal conduct as both stunt brain development.