Moving beyond nature versus nurture in forensic psychology

It is important to understand the role of both biological and environmental factors in criminal behaviour in order to enhance our understanding and guide the development of interventions. This essay will focus on research into the development of antisocial and criminal behaviour in children and adolescents in order to explore the relationship between biology and environment and demonstrate that forensic psychology has moved beyond simple nature versus nurture arguments. The essay will focus on antisocial behaviour rather than aggression as aggression is not always of a criminal nature or intent (School of Psychology, Module 2: Psychology, the legal system and criminology, 2009).

Explanations of criminal behaviour that focus on an individuals physiological functioning are said to be examinations of the ‘nature’ of criminality with a focus on criminals being born and not made. However, many criminologists reject the notion of there being a biological basis for antisocial behaviour believing it encourages the view that there are inherent genetic flaws in criminals and therefore treatment is not possible. Genetic explanations for criminality risk leading policy makers and treatment providers to ignore wider social issues that may impact upon a person’s propensity to commit crime. Also, if we were to assume that the presence of certain genes was indicative that a person would become a criminal this could potentially lead to a society where we imprison people for possession of certain biological characteristics. By offering a purely ‘nature’ argument in explanation of criminal behaviour this may imply that perhaps treatment and rehabilitation from a psychological perspective are invalid. It also can be argued that such an approach removes the responsibility for action away from the offender.

Conversely, nurture arguments focus attention on how criminals might be made i.e. examining social and environmental factors such as a person’s upbringing and home circumstances. Whilst these are important factors the evidence available suggests that the presence of poor environmental factors does not always lead to the development of antisocial behaviour in those exposed to these environments.

There are, therefore, many factors that impact upon an individual’s predisposition to commit a crime and these will be considered in this essay to demonstrate the importance of considering both nature and nurture factors in criminal behaviour.

First this essay will examine literature that explores the genetic basis of behaviour. Next key studies that have considered the effect of environment on antisocial behaviour will be explored. Finally, literature that considers both genetic / biological factors and the environment will be considered and shown to be a more coherent account of the development of antisocial behaviour.

A substantial amount of literature exists that examines which genetic and environmental differences may increase the risk of someone engaging in anti-social behaviour. There are three main methods used to explore these factors- family studies, twin studies and adoption studies. As with all studies of criminal behaviour the findings will depend on both the definitions of criminality used and the data that was utilised.

The nurture debate

The importance of understanding the role of nurture in the development of anti-social behaviour has been explored through numerous studies of families. Family factors that contribute to antisocial behaviour have been demonstrated through a variety of studies examining both community and clinical samples. For example, Loeber & Farrington (2001) showed that maltreatment, family violence, parental psychopathology and familial antisocial behaviours were all risk factors for criminal behaviour. Poor parental supervision, erratic or harsh discipline, parental conflict and low parental involvement in the child’s life have also been found to be important predictors of juvenile offending behaviour (Loeber & Stouthamer-Loeber, 1986). However, it must be noted that some of these factors (e.g. poor parental supervision, harsh discipline) are open to subjective interpretations depending on the methodology used and as such comparisons across studies may be questionable. Additionally, community factors have also been identified as relevant including poor school achievement, living in poverty and living in an underprivileged area as relevant contributory factors (Loeber & Farrington, 2001).

In further exploration of familial factors, the role of environment has been considered in the field of personality disorders which attract much attention from both policy makers and the media, and of particular relevance to this essay is antisocial personality disorder (ASPD). Research indicates that if parents have a diagnosis of ASPD then they are significantly more likely to have children who display symptoms of conduct disorder – an early indicator of ASPD (Foley, Pickles, Simonoff, Maes, Silberg, & Hewitt, 2001; Frick, Lahey, Stouthamer-Lober, Christ & Hanson, 1992; Lahey, Hartdagen, Fryck, McBurnett, Connor & Hynd,1988). Children whose parents have an ASPD diagnosis have been found to be over three times more likely to develop ASPD in adulthood than children born to parents without this diagnosis (Kendler, Davis & Kessler, 1997). In support of these findings, Herndon & Iacono (2005) found that children whose parents exhibited antisocial behaviour were at increased risk of developing similar antisocial traits in adolescence.

These studies highlight that antisocial behaviour appears to be passed through family generations. However, many of these studies focus on fathers and sons and the limited findings on women and their daughters are inconsistent. More research is needed to understand if there are gender effects in the familial transmission of antisocial behaviour. Crucially, family studies do not allow us to understand how antisocial behaviour is passed between generations and it can not be assumed from the studies cited that the process is purely one of familial transmission. Indeed it is unlikely that antisocial behaviour is either entirely an environmental or entirely a genetic process. For this reason, twin and adoption studies are often used to try and further establish the role of genetics and environment in the development of antisocial behaviour. Such studies are often considered a more valid way of understanding the nature / nurture debate as they consider both sides of the debate. It is important to note however that the factors discussed in this essay should not necessarily be considered to be causal factors in the development of antisocial behaviour and should instead be viewed as risk factors (Plomin & Colledge, 2001).

Twin and adoption studies

Twin studies have often been used to explore the contribution of biological factors to antisocial behaviour. There are two different types of twins – identical monozygotic twins (MZ) who have the same genotypes, and fraternal non-identical dizygotic twins (DZ) who have only half their genes in common. As MZ twins have identical genes the argument follows that if the environment is the same then these twins should exhibit more behavioural similarities than DZ twins who only share on average 50% of their genes (Hollin, 2001). Other research in this area has studied twins and their non-twin siblings. Twin studies have shown significant genetic components for child and adolescent antisocial behaviour (Edelbrock, Rende, Plomin & Thompson, 1995; Gottesman & Goldsmith, 1994; Pike, McGuire, Hetherington, Reiss, & Plomin, 1996).

Many of the twin studies are small in sample size and as such their results must be interpreted cautiously. Also, some commentators believe that it is possible in earlier studies that twins were misclassified as either MZ or DZ making the research findings potentially invalid (Blackburn, 2002). A further difficulty is that much of the research has studied twins who have been raised in the same environments resulting in a limited ability to specifically determine the role of both nature and nurture.

Although the findings of twin studies can be criticised, adoption studies have also claimed to have identified a large genetic component in the development of criminal behaviour. For example, Crowe (1974) found increased rates of criminality in adoptees whose biological mothers had criminal histories. However, the sample size for this study was only 37 making it questionable in terms of validity and reliability. In support of this finding a more robust study, (Cadoret, 1978), with a sample of 246 adopted children, found more antisocial behaviour in those children whose biological parents displayed antisocial behaviour traits. Similarly, Bohman, Cloninger, Sigvardsson and von Knorring (1982) found that criminal behaviour in adopted children was associated with criminal behaviour from their biological parents. However, this study only found this relationship in property crime meaning that the results can not be extrapolated to account for more general criminality. Also the studies only gathered data from the children at one particular time in their lives limiting our understanding of the stability of anti-social traits. In response to this limitation, more recent studies have taken a longitudinal approach and these have also demonstrated that adoptees’ conduct disorder and antisocial personality disorder are related to their biological inheritance (Cadoret, Yates, Troughton, Woodworth & Stewart, 1995).

The brief discussion above demonstrates that adoption studies have lent further support to the argument that there is a genetic influence on criminal behaviour. However, as the adopted children are being raised by parents who will not share their genetic inheritance there may also be an environmental element which influences behaviour that is not clear from this research. A further complication with some of the adoption studies is that it is not always clear whether the children were adopted at birth or not so we can not know whether early environmental experience has exerted influence on some of the children’s behaviour prior to their adoption. As with twin studies, adoption studies also often have small sample sizes making it necessary to interpret the results with some reservation.

Despite the evidence for genetic influence on antisocial behaviour there are inherent dangers in examining only biological influences on antisocial behaviour. Such an approach may limit opportunities to intervene as a person is considered to be predisposed to commit crime and therefore nothing can be achieved by psychological or environmental interventions (Rutter, 1997).

Nature and nurture

The continued rise in crime can not be attributed solely to a change in the biological makeup of the people in our society demonstrating the need for consideration of other factors that may be of relevance (Rutter,1997). Having very briefly examined studies which consider the role of nature or nurture in the development of antisocial behaviour and highlighted the flaws of this research it is apparent that studies that consider the role of both nature and nurture are of crucial importance in furthering our understanding.

In adoption literature, studies which consider the role of the adoptive parents as well as the biological parents can further our understanding of the effect of environment on antisocial behaviour. There is also now an increasing literature considering shared environmental effects, non-shared environmental effects as well as genetic effects using twins and adoptees as their sample. However, as previously stated the use of small sample sizes is a fundamental limitation of studies particularly when studying a number of variables such as shared environmental influences alongside genetic influences. Martin, Eaves, Kearsey, & Davies, (1978) concluded that at least 7,000 twin pairs would be necessary to reliably detect shared environmental influences of 10%. Any conclusions regarding the role of the shared environment should thus be made cautiously when examining studies with small sample sizes.

Twin and adoption studies that have examined the role of genetic and environmental influences on various forms of antisocial behaviour have consistently shown support for both of these variables (Rhee & Waldman, 2002). The majority of support has been found for genetic factors being significantly related to both antisocial behaviour and conduct disorder. In a sample of 2,682 adult twin pairs, Slutske, Heath, Dinwiddie, Madden, Bucholz & Dunne (1997) reported that 71 percent of the variance in the aetiology of conduct disorder was a result of genetic factors. Similarly, a recent British twin study (Arsenault, Moffit, Caspi, Taylor, Rijsdijk, Jaffee, 2003) found that 82 percent of the development of childhood antisocial behaviour was explained by genetic factors. Such studies posit that genetic factors seem to hold a stronger influence than environmental factors when considering antisocial behaviour.

Studies of adoptive parents’ antisocial behaviour have considered the effect of being raised by antisocial parents in conjunction with the effect of having heritable antisocial traits. A large adoption study (Mednick, Gabrielli & Hutchings, 1984) showed that having a convicted adoptive parent was associated with a slightly increased risk of criminal conviction in the child. There was a further increased risk of conviction for the children whose biological parent had criminal convictions. Of note however was the finding that if the child had both adoptive and biological parents with criminal convictions then they were shown to be at the highest risk of all the groups of being subsequently convicted themselves. Furthermore, in an analysis of three studies a significant increase in antisocial behaviour was found when an adopted child had both a genetic risk factor and an adverse environmental factor present (Cadoret, Cain & Crowe, 1982). These studies provide evidence for both nature and nurture and highlight that when both genetic and environmental factors are present then the risk of the development of antisocial behaviour is substantially increased.

In contrast to the Mednick et al study (1984), Cadoret, Troughton & O’Gorman (1987) found that adoptive parents’ anti-social behaviour had a larger influence on the adopted children’s behaviour than their biological parents did. This study therefore suggests that the environment a child is raised in can exert a significant amount of influence on future behaviour. Although these two studies highlight a mixed picture as to whether it is nature or nurture that has the most impact on a child’s behaviour they both demonstrate that environment and biological factors do have an influence. What remains to be clarified is what processes need to be present in an environment in order for a child to develop antisocial and criminal behaviour. It is also important to note that many researchers have highlighted that potentially families who choose to adopt may not be a representative sample of the population as a whole, meaning that such research can not be generalised beyond adoptive families.

As discussed, numerous twin and adoption studies have examined the contribution of genetics and shared and non shared environments to the development of anti social behaviour but the studies are often vastly different in the figures they produce (Rhee & Waldman, 2002) making it difficult to reach a firm conclusion about the contributions of each factor. To address this issue meta-analytic studies have been undertaken and can be considered an effective way of synthesising the available literature in an attempt to establish whether there are consistent findings across studies. Meta-analytic studies also provide the large sample sizes required in order that appropriate effect sizes can be calculated resulting in more valid and meaningful results.

Walters (1992) analysed 38 twin and adoption studies in an attempt to clarify the role of genetics and environment on crime and found some support for the hereditary basis of criminality. This study found that the strongest correlation accounting for 65% of the variance was for individual environmental factors. In a larger study, Rhee & Waldman (2002) conducted a meta-analysis of 51 twin and adoption studies that examined genetic and environmental influences on antisocial behaviour. They found that genetic influences accounted for 32% of the variance, environmental influences accounted for 16% of the variance and non-shared environmental influences explained 43% of the variation in anti social behaviour (Module 2 Handbook) giving greater weight to supporters of interventions based on environmental factors.

In an enhancement to the above meta-analyses, one study (Mason & Frick, 1994) found that it was the severity of the antisocial behaviour that was key, with genetic effects showing a more significant contribution the more severe the antisocial behaviour was. They found that 50% of the variance in measures of antisocial behaviour was attributable to genetic effects with even larger genetic effects found for what they termed as “severe manifestations of antisocial behaviour” (Mason & Frick, 1994). It appears then that even meta-analytic studies can not provide a definitive answer to the contribution of biological and environmental influences in the development of antisocial behaviour.

As with all research methodologies it is important to note the flaws of meta-analysis. When considering a range of studies it is possible that comparisons and combinations of data is inaccurate. As the researchers are not always able to access the primary data they must rely on that which is provided by the original study. This may not contain all the relevant information required to make accurate syntheses of the literature and there is a danger of incorrect assumptions being made.

Findings across studies vary therefore in their estimates of the role of genetics and environment on the development of antisocial behaviour. It is important therefore to consider the presence of moderators of these risk factors. Researchers have begun to consider what factors may have a moderating effect on the role that genetic and environmental factors play.

Different patterns of antisocial behaviour have been studied to try and further understand the role of genetics and environment in the development of antisocial behaviour. A number of studies have examined whether genes or environment play different roles at different times in an individuals life. The findings of this research however are inconsistent. Some studies have found that the influence of genetics can be found to increase as the person gets older (Goldstein, Prescott & Kendler, 2001, Jacobson et al. 2002) whereas Rhee and Waldman’s (2002) meta-analysis found that genetic and environmental factors exerted less influence as individuals aged. Again, as mentioned previously these differences in results may be as a result of methodological issues so there remains a need for further research in this area.

Beyond genetics

Although much nature versus nurture research focuses on genetics and on environments in which children are raised there is also evidence to suggest that there are other biological factors which, combined with adverse environmental factors increase the likelihood of an individual of developing anti social behavioural traits.

Research indicates that birth complications may often predispose children to cognitive deficits. Such deficits have been regularly found to have a link with antisocial behaviour in childhood and adolescence, particularly when adverse environmental factors are also present (Module 2 handbook). Recently it was found that children with birth complications that affected their IQ were at increased risk of developing behaviour problems (Liu, Raine, Wuerker, Venables & Mednick, 2009). Raine, Brennan, and Mednick (1994) found that 4% of a sample that had both birth complications and experienced early maternal rejection were responsible for 18% of all the violent crimes committed by an entire sample of over 4000 children. Beck and Shaw (2005) found that if a child was raised in adverse family circumstances and had birth complications then antisocial behaviour was likely to occur in adolescence. Similarly, children that had experienced birth complications and were subsequently raised in an unstable family environment displayed almost double the amount of violence in adulthood when compared to sub-groups that had only one of the risk factors present. The group with both risk factors present also displayed significantly more behavioural problems in adolescence (Raine, Brennan, Mednick & Mednick, 1996). These studies demonstrate that other biological factors, beyond genetics may effect the development if antisocial behaviour, particularly when the child is raised in an environment which presents further risk factors.

In addition to the examination of specific factors such as birth complications, researchers have also considered whether there is a more dynamic process in the development of criminality with consideration given to whether an individual’s biology and genetics may interact with their environment. The scope of this essay does not allow a thorough exploration of this area and the literature is still emerging. As such a brief consideration of the findings to date is presented.

The theory of ‘evocative biology-environment correlation’ (Ge, Cadoret, Conger, Neiderhiser, Yates, Troughton & Stewart, 1996) may offer a more complete account for the role of nature and nurture on the development of antisocial behaviour. This theory considers how an individual’s heritable behaviour may evoke a particular response from their environment. The dynamic nature of the interaction between biology and environment can be demonstrated in a study that found that in addition to the heritability of antisocial behaviour from biological parents, adoptee’s antisocial behaviour and adoptive mother’s parenting practices have an effect on each other and can contribute to further antisocial behaviour in both the child and the adoptive parents (Ge et al, 1996). Further studies that have considered whether adopted children’s aggression which has a genetic basis might predict the parents’ response to them (O’Connor, Deater-Deckard, Fulker, Rutter & Plomin, 1998; Riggins-Caspers, Cadroet, Knutson, & Langbehn, 2003) have found that if the adopted child is at high genetic risk for antisocial behaviour then they receive higher levels of discipline and control from their parents. The few studies available in this area consistently show that the parenting children receive is mediated by the child’s genetically influenced behaviour problems (Moffit, 2005).

Conclusion

It is not possible to account for the causes of criminal behaviour by simply referring to either nature or nurture (Pakes & Pakes, 2009) which can be considered rather a rudimentary approach. Research continues into the various contributions of biological and environmental factors and their impact on criminal behaviour. We have therefore moved beyond the nature versus nurture arguments to a position where criminality needs to be understood through reference to a variety of contributory factors biological, psychological and environmental. It must also be noted that research does note as yet provide causal explanations, rather it highlights factors that predispose an individual to antisocial behaviour. (Arsenault, Moffitt et al, 2003). It may well be that it is the combination of the presence of a number of risk factors that offers us the most complete explanation for antisocial behaviour. Also as the majority of the research uses twin and adoption populations whether the findings can be generalized across parenting settings remains unclear.

It seems that for a genetic potential for criminal behaviour to be realised then certain environmental factors may also need to be present. It does seem that for children with genetic vulnerabilities who are also exposed to adverse environments their risk of developing antisocial behaviour is increased. It is also possible that a child with genetic risk factors for antisocial behaviour may also evoke negative parenting. Findings are consistent across studies so it appears that there is evidence to suggest the need for interventions that target families with ASPD diagnoses in an attempt to break the cycle of transmission of antisocial behaviour. It may be pertinent for their families to be targeted to attend programmes such as “Triple P” as recommended in government guidance.

Nature and nurture can not be considered to act independently of one another in influencing the development of anti social and criminal behaviour. It is more reasonable to argue that genetic effects on behaviour may either influence the extent to which the individual is likely to be exposed to particular environments or affect how susceptible the individual is to negative environments.

There is overwhelming evidence therefore that criminal behaviour is a complex interplay between biology, environment, experience and other factors. As each factor does not on its own lead a person to criminal or antisocial behaviour opportunities for intervention are available.