4.3 Structural explanations I: biology

There is a long and uneven tradition of claims that the origins of crime and deviance are biological. In the nineteenth century it was claimed, for example, that brain sizes and skull shapes could explain criminal behaviour. This kind of crude biological determinism has long been discredited, but it gave way to a more subtle and notionally scientific model of genetic determinism.

In the early twentieth century advocates of eugenics claimed to have created the science of improving humanity. They argued that social behaviour could not only be studied with the methods of the natural sciences, but that a social science which modelled itself on the natural sciences could, as medicine discovers the pathological causes of illness, discover the pathological causes of crimes. According to eugenicists at the time, certain groups of people – variously, the poor, aliens and foreigners, the mentally ill or disabled and criminals – possessed incurable genetic defects. These defective and dangerous people threatened the genetic purity of the healthy, and the moral values and fibre of the social order. Moreover, eugenicists worried these groups were likely to reproduce more defective and dangerous people. Taken to their extremes, these arguments underwrote programmes of sterilisation of the mentally ill and of criminals all over Europe; most enthusiastically by the Nazi regime.

While eugenics has long been discredited, biological and genetic arguments continue to re-surface in criminological debates. The new genetic determinism of the late twentieth century is backed up by a much more explicit biological understanding of what genes actually are. Genes are particular parts or segments of the DNA strands that sit in the nucleus of every living cell. Genes are in effect biochemical codes that, through a variety of mechanisms, control and shape the development and operation of cells and thus in turn whole organisms. Moreover, when cells divide their DNA passes on to the new cells. When organisms sexually reproduce, the DNA of both parents is combined and transferred to their offspring. The new genetics argues that many patterns of human behaviour can be traced back to an individual's genetic endowment or their inherited genetic and biological structures.

Probably the most rigorous research in this tradition has been associated with the study of twins and of adopted children. There is a large body of research which suggests that identical twins, when compared with non-identical twins, are much more likely to display similar tastes, talents and patterns of behaviour, not least known criminal offending (Christiansen, 1977). (Identical twins share the same genetic make-up as opposed to non-identical twins who share a womb, but possess different genes.) However, it has been widely noted that identical twins are treated by their families and their schools as much more alike than non-identical twins. Therefore, their criminal behaviour may be largely explained by their shared social experiences rather than their shared genetic endowments.

According to the leading exponent of genetic explanations of criminality, Sarnof Mednick, the study of adoptions better separates social and genetic effects or structures than twin studies (Mednick et al., 1987, p. 74). The central proposition of Mednick's research in this area is that adopted childrens’ criminal behaviour is more similar to their biological parents’ criminal behaviour than their adoptive parents. On the basis of his analysis of research findings from Denmark, Mednick argues that there is indeed a stronger relationship between the criminality of the adopted child and their biological parents, than there is between the adopted child and their adoptive parents. This relationship is particularly strong amongst chronic, persistent criminal offenders.

In related research, Mednick and his colleagues have tried to find a more precise biological mechanism that links possession of a certain gene to a biological characteristic of an individual, and in turn how this links to, or structures, criminal behaviour. They claim to have discovered a particular pattern of inherited autonomic nervous system (ANS) characteristics amongst known offenders. The ANS is the unconscious part of the nervous system connecting the brain to our internal organs, senses, skin and muscles. Mednick argues that criminal offenders tend to have an ANS which is less sensitive to environmental stimuli than non-offenders. This creates personalities and dispositions that are less alertly tuned to the world, slower to respond to external signals and more easily distracted. As a consequence these individuals are less likely to respond to all the social messages and constraints that exist against acting criminally or in an anti-social fashion. In short they are less likely to be inhibited in displaying anti-social behaviour.