Some scientists think that certain genetic characteristics may give rise to a predisposition to criminal or violent behaviour. Some people may be genetically ill-equipped to cope with frustration or other emotional crises. The impairment of intelligence caused by chromosome defects may give rise to sociopathic behaviour in individuals. Neurotransmitters such as serotonin, norepinephrine and dopamine may also play a role in provoking violent behaviour.
In 1965, scientists claimed that an abnormally large proportion of sociopathic offenders in two special hospitals in Scotland had extra chromosomes. It was referred to as the XYY syndrome. This seemed to be the confirmation of ancient moral theory that people were waiting for, namely that criminals were born, not made. Five years later, a study published by the Cambridge University Institute of Criminology summarized and clarified the facts: (a) There is no doubt about the correlation between the double Y chromosome, criminality and anti-social behaviour increasing in frequency with decreasing intelligence. (b) The patients being genetically disposed to criminality are unlikely to respond to punishment. (c) The extra Y chromosome has resulted in a severely disordered personality, and this disorder has led these men into conflict with the law.