Genetics and Human Behaviour: The Ethical Context
Previous genetic and physiological explanations of crime
XYY males
14.5 In 1965 a paper was published based on research involving almost 200 males who had been committed to the State Hospital at Carstairs in Scotland.(3) Seven of the men were found to have an extra Y chromosome, a much higher rate than was thought to be the case in the general population. The research raised the possibility that this genetic abnormality could be related to the aggressive behaviour of the inmates. Further research showed that XYY males were more likely to be taller than average and of low intelligence, but failed to provide conclusive evidence about a link to aggressive or violent behaviour.(4) In 1976 a paper was published which concluded that XYY males were more likely to be imprisoned, but that this was due to their low intelligence and low socioeconomic status which placed them at higher risk of being caught.(5) The current state of opinion on the XYY issue is that there is insufficient evidence to establish any firm link between the particular genotype and an increased risk of aggressive behaviour, although there does appear to be an increased risk of offending.
14.6 There are no legal cases in the UK in which a genetic diagnosis of XYY has been used to establish a defence. At least five major US cases attempted to use the fact that the accused was XYY in defence but none was successful. In one, State v Roberts (1976), the judge stated that ‘presently available medical evidence is unable to establish a reasonably certain causal connection between the XYY defect and criminal conduct’.(6) We discuss the issue of the quality of scientific evidence that is admissible in the legal system in paragraph 14.23. In the case of XYY males, it is highly unlikely that the syndrome will acquire legal significance because of the difficulty in showing that it is directly linked to forms of antisocial behaviour.
14.7 It is perhaps worth making the observation here that having just a single Y chromosome is highly correlated with criminal behaviour: the vast majority of the prison population in the UK are men. This correlation does not seem to generate the same concerns, in that ‘being male’ is not suggested as something that absolves individuals from responsibility for criminal acts, nor is it taken into account as a mitigating factor in sentencing. We consider the relevance of the frequency of a genetic trait or predisposition in the population with regard to predicting behaviour in paragraph 14.38.
Syndromes
14.8 Numerous syndromes have been claimed to weaken or eliminate moral responsibility in cases where the accused person pleads not guilty by reason of insanity. These include syndromes thought to arise as the result of an environmental trauma, for example battered spouse syndrome, battered child syndrome and post-traumatic stress disorder, and those thought to arise as the result of a biological condition, such as premenstrual syndrome and postnatal depression. In these ‘biological syndromes’, the argument is that chemical or hormonal changes in the body affected the individual’s capacity to control their actions to such a degree that they cannot truly be said to be responsible for them. The defence of premenstrual syndrome has been successful in Britain but is now rarely used because there has been a subsequent increase in measures to improve early detection and prevention of the condition.
Genetics: Huntington’s disease
14.9 Huntington’s disease, a single gene disorder that may be associated in some cases with aggressive behaviour, has obvious implications for criminal law. A person with this disorder may behave irrationally and may carry out assaults with no apparent motive.(7) Such behaviour is, of course, more easily seen as a concomitant of illness than is the case with asymptomatic genetic conditions, and is therefore more likely to be treated by the courts as an exculpatory factor. Prosecutorial discretion often prevents the bringing of charges against a person suffering from a diagnosed and obvious condition, such as dementia, and it is for this reason that legal precedents do not articulate the implications for criminal guilt of such conditions. The important point to note, however, is that it is not the genetic mutation which is regarded as exculpatory here but its impact on the brain. If a person suffering from Huntington’s disease were to be acquitted of a criminal charge relating to aggressive behaviour produced by the condition, then this would be on psychiatric rather than on genetic grounds.
Genetics: Monoamine oxidase A (MAOA) deficiency
14.10 As noted in Chapter 9, there has been very little research on individual genes that might influence antisocial behaviour or criminal activity, with the exception of the family whose male members were deficient in a protein called MAOA. These males were found to be more likely to have been convicted of aggressive crimes such as rape and arson. Since this finding is currently confined to members of one family, it seems unlikely that it will have an impact in the legal system.(8) However, as we noted in paragraph 9.25, one recent study has suggested that the MAOA genotype may be a relatively effective predictor of antisocial behaviour in children who are also maltreated.
3 Jacobs, P.A. , Brunton, M. , Melville, M. M., Brittain, R. P. & McClermont, W. F. (1965). Aggressive behaviour, mental subnormality and the XYY male. Nature 208, 1351-2.
4 Baker, D., Telfer M. A., Richardson, C. E. & Clark, G. R. (1970). Chromosome errors in men with antisocial behavior: comparison of selected men with ‘Klinefelter's syndrome’ and XYY chromosome pattern. JAMA 214, 869-78; Jacobs, P. A., Price, W. H., Richmond, S. & Ratcliff, B. A. W. (1971). Chromosome surveys in penal institutions and approved schools. J. Med. Genet. 8, 49-58; Schiavo, R. et al. (1984), Sex, chromosome anomalies, hormones and aggressivity. Arch. Gen. Psychiatry 4, 93-9.
5 Witkin, H. A. et al. (1976). XYY and XXY men: criminality and aggression. Science 193, 547-55.
6 State v Roberts (1976). 14 Wash. App. 727, 544 P.2d 754.
7 Mild psychotic and behavioural problems can appear some years before the onset of the disease. A study by Danish researchers in 1998 found increased prevalence of criminal behaviour in men with the genetic mutation that causes Huntington’s disease and concluded that this was linked to the personality changes that are often seen in people with the condition (Jensen, P., Fenger, K., Bolwig, T. G. & Sorensen, S.A. (1998). Crime in Huntington’s disease: a study of registered offences among patients, relatives and controls. J. Neurol. Neurosurg. Psychiatry. 65, 467-71).
8 In Mobley v State (1995). 265 Ga. 292, 455 S.E. 2d 81 the defence lawyers of a man accused of murder attempted to have their client tested for MAOA deficiency. However, the court refused to allow such a test, saying that ‘the theory of genetic connection … is not at a level of scientific acceptance that would justify its admission’. The request was made as a potential mitigating factor, not an exculpatory factor, in an attempt to avoid the death penalty.