Genetic and Environmental Factors for Criminality

  • Is a crime committed because the criminal is a rational being, able to make the decision to offend as an act of free will?
  • Does the crime occur because environmental influences – parents, peer group, culture and so on – determined the act would invariably happen?
  • Or is the real clue to be found in the genes: are criminals born not made?” (Hollin, 1989, p.3-4)

Discuss each of these perspectives and consider which theory (or combination of theories) is the most plausible and why?


What motivates individuals to commit crimes, particularly violent crimes against other individuals has been the subject of research in criminology for over two hundred years. Globally the search for the causes of crime continues to form the bedrock of most criminological studies (McLaughlin et al., 2003, p.73).The nature versus nurture debate in respect of criminology has been central to the research, having been especially intense, and often emotional in explaining criminal behaviour (Sarbin and Miller, 1970). The debate regarding the relative impact of genetics and environmental influences continues to inform a considerable body of research.

In respect of commission of crime two distinct schools of thought have dominated the debate. Classical criminologists approach the question from the standpoint of individuals having, and employing, a free will. They take no account of the circumstances or environment in which an individual has been formed, taking the view that a criminal commits a crime because he wants to, the deed depending only on the voluntary determination of the individual (McLoughlin et al., 2003, p.53).

On the other hand are those who believe that an individual acts in a certain way as a result of the circumstances in which he finds himself. It is only when the circumstances conspire against an individual that he will commit a certain criminal act, but this will not happen simply as a consequence of his wanting to (McLoughlin et al., 2003, p.53). Those approaching the problem from this point of view believe that intervention programmes and improvements in circumstances could reduce levels of violent crime in society.

The aim of this paper is to investigate these theories and the evidence in support of each of them. I will conclude with a consideration of which is the most plausible theory, or combination of theories, following on from the arguments given.

The Concept of Crime and Criminology:

Criminal acts may, in their simplest form be thought of as acts which are prohibited by the law and they can be specific to a particular culture, what is acceptable in one, being unacceptable and unlawful in another. There have been wide ranging definitions of what constitutes crime, but this has been problematic as there is no general agreement on what crime is (Jones, 2006).The fact that crimes do not constitute natural or homogenous behavioural categories poses particular difficulties in identifying the subject matter of criminology and for constructing theories of “crime” and “criminal behaviour” (Blackburn, 2000, p.16). Because of the difficulties faced in defining the patterns of behaviour associated with criminality, there is an associated difficulty in isolating the causal effects of intrinsic and extrinsic factors and the extent to which these exert an influence on an individual’s behaviour. More and more evidence is suggesting that the criminal justice system is home to individuals with psychological problems. The fact that many of these problems have been shown to have a genetic component suggests that individuals could find themselves engaging in criminal activity (Jones, 2005). In order to address this problem and effectively treat the individuals involved, it is necessary to attempt to establish the causes of these psychological problems.

Criminal Behaviour:

Criminal behaviour is defined in the context of the legal structure adopted by a society. It is a widely held view that criminal behaviour falls within the realms of anti social behaviour. The influence of genetic components on anti social behaviour has been investigated by Morley and Hall. They suggest three different ways to define anti-social behaviour as follows:

  • Anti-social behaviour can be equated with criminality and delinquency, with individuals involved being liable to arrest and involvement in the criminal justice system which may include prison;
  • Anti-social behaviour can be defined as a result of personality disorders, particularly anti social behaviour problems which lead to an increased risk of involvement in criminal behaviour;
  • Anti-social behaviour can be defined as a measure of personality traits, which can lead to an increased likelihood of engaging in criminal behaviour. These include aggression and impulsiveness, both of which have been associated with increasing levels of criminal behaviour.

(Morley and Hall, 2003, cited in Jones, 2005).

Genetic Factors:

Family studies have been the focus of research for quite some time. While the early studies in this area suggested that there was an inherited basis for a predisposition towards criminal activity, it was shown that environmental influences could modify an individuals characteristics and personality (Joseph, 2001). Research like that carried out by Joseph was questioned largely in methodological terms, but nonetheless raised important questions which became the focus of a great deal of further research (Jones, 2005). In recent years the study of genetics, largely as a result of more sophisticated techniques, has become one of the fastest moving and most significant areas of modern science (Williams, 2004, p.131), giving an enormous insight into the make up and working of the human body, including the mind. Human behaviour patterns are generally accepted to be an interaction of life experiences and genetic predispositions (Mednick et al., 2003, p.77), with an acceptance of biological explanations only suggesting that criminals are inherently defective (Blackburn, 2000, p.136).

The idea that genetics are a factor in criminal behaviour has existed for a very long time, one of the earliest studies in this area being carried out in 1877 by Richard Dugdale. His work investigated the criminal behaviour of a notorious American family called the “Jukes”, six of whom Dugdale had encountered in prison. When tracing their family tree over a period of two thousand yeas, Dugdale found a history of poverty, prostitution, and crime. With no scientific basis for his supposition, he attributed this to the “degenerate nature of the family, and despite the lack of scientific support, the work was very influential at the time. He did not consider the fact that the family members were being impacted upon by the same or very similar environmental factors which could have impacted substantially on their behaviour.

By the end of the nineteenth century, scientific theories in respect of heredity had taken on increasing importance and were being supported by empirical evidence, albeit doubtful in validity. Another early writer, Goring, suggested in 1913 that criminal tendencies were basically inherited. He studies convicts from the same families and found that the correlation for criminal behaviour was very similar to that for some physical characteristics such as eye colour, and stature, suggesting that the genetic material passed on by parents was vital in shaping the way their children would turn out. Parents who were criminals would pass this trait on to their children in the same way in which they might pass on any other characteristic (Goring 1913, cited in Williams, p.132).

Twin Studies:

Twin studies have been important in trying to establish links between genetics and subsequent behaviour. There are two types of twins:

  • Monozygotic twins come from the same egg. They are commonly known as identical twins, although this is, in fact, incorrect. They have the same genetic structure, are the same sex and have a very similar physical appearance.
  • Dizygotic twins occur when two eggs are fertilised simultaneously and are no more genetically similar that any two siblings.

It could therefore reasonably be said that if monozygotic twins were to behave in the same way, for example in criminal behaviour, this could be attributed to some sort of genetic influence. If crime is related largely to environmental influences, then it would be safe to assume that all twins would have the same chances of future criminal behaviour. Studies involving twins have been notoriously difficult because of the very similar environment in which they grow up, making it difficult to isolate genetic from environmental influences. The chances of monozygotic twins who are separated would be the ideal for the purposes of research but, due to the fact that twins are not often separated, the sample on which research can be based has traditionally been small.

Such studies have nonetheless been carried out, one of the earliest of which was undertaken by the German physiologist Johannes Lang. he studied pairs of criminal twins and found that in 77% of cases concerning monozygotic twins, where one twin had a criminal record, not only did the other twin also have a record, but the patterns of the offences were similar in nature. In a group of dyzygotic twins, the correlation dropped to 12%, falling to only 8% when pairs of brothers were compared. The studies were subject to methodological flaws in so far as the identification process was based on observation only, and many of the twins came from psychiatric clinics which may mean that the chances of criminal behaviour were increased from the outset (Jones, 2006).

Christiansen attempted to overcome some of the methodological problems of earlier work when he studied the entire database of twins in Denmark. For both male and female twins he found that the rates of offending were more highly correlated for monozygotic than for dizygotic twins. He also found that the more serious the offence, the stronger was the potential genetic component. He was nonetheless aware of the difficulty in separating genetic and environmental factors which he acknowledged in his work.

Adoption Studies:

Adoption studies have been central to research which has attempted to establish the relative roles of genetics and the environment in determining an individual’s behaviour. The rationale behind these studies is that if children adopted soon after birth resemble their biological parents more than their adoptive ones, the evidence points towards genetic rather than environmental explanations. One of the earlier studies in this field was carried out by Hutchings and Mednick in 1975. They compared adopted children whose fathers had criminal records with adopted children whose father did not. They reported a higher incidence of criminal behaviour in those children whose fathers had criminal records than in those whose fathers did not (cited in Towl and Crighton, 1996, p.15). These findings have been refuted by a number of subsequent studies which have suggested that these findings are unreliable, as only a very small number of adopted children engage in criminal behaviour in adulthood. Stott has suggested that it is more likely that the predictor of this criminal behaviour is the result of problems encountered by mothers during pregnancy. Many of these problems are most prevalent in low socio economic groups which is typically the tier to which mothers who have their babies adopted tend to belong. He argues that it this rather than the operation of any genetic factors which accounts for the relationship between criminality in adopted children and their biological parents (Stott, 1982).

Family Studies:

Studies in this area which have attempted to ascertain the relative influences of genetics and the environment, have been largely unaccepted in academic circles. The most salient problem inherent in research of this nature is the notoriously difficult task of separating the nature from the nurture effects and therefore establishing causal links. While this is a problem that is also inherent in the twin studies, it is more apparent in family studies when the genetic similarity between siblings is less.

Mednick and his colleagues tried to address this methodological issue when they investigated rates of criminal behaviour in children of criminal parents who had been adopted and were not therefore exposed to their parents. They found that the children of such parents were indeed more likely than the population in general to engage in offending behaviours, but that the genetic explanation did not account for the types of criminal behaviours these would be. They concluded that there was at least some genetic component in the commission of criminal behaviours (Mednick et al., 2003, p.89-90).

Biological Factors:

Recent research has suggested that characteristics observable at birth will develop in the context of the circumstances in which an individual finds himself. Manicus asserts that it is brain activity that provides the causal mechanism for behaviour thereby making biological processes as real a cause of crime as social processes (Manicus, 1987). Many studies have suggested that crime does, in fact, run in families. Research conducted by Blair and colleagues has pointed to a genetic component in the development of psychopathic tendencies. They suggest that as well as this genetic component, complications during the birth of some babies are a strong risk factor for later violent and anti social behaviour, but recognise that intervention and helping parents could be an important component of ensuring that such behaviour does not subsequently manifest itself (Blair et al., 2006). Problems encountered by mothers during pregnancy has been attributed to subsequent criminal behaviour.


Recent advances in the field of genetics have led criminologists to look at the role of chromosomes in the criminal behaviour. In particular scientists have investigated the sex chromosomes and their possible role in crime causation. This research began in 1965 when a British researcher, Patricia Hayes, examined chromosomal abnormalities in a group of Scottish prisoners. The blood test employed, a technique called karyotyping, revealed that twelve out of the 197 examined showed abnormalities in their chromosomes while seven were found to have an XYY chromosome. Normal males possess an XY chromosome, and while there are several different permutations of the chromosome, the XYY male was identified as potentially very dangerous and termed a “supermale.”

A number of criminals have subsequently tried to offer this a defence saying that this biological trait was what spurred them on to criminal activity. This defence was successfully used in 1969 in Australia by one Lawrence E. Hannell, judged a “supermale” and subsequently released on the grounds of insanity. Other attempts have not been so successful. When such an attempt was made in the case of Richard Speck, accused of killing a number of his classmates in the United States, he was not acquitted and it was later revealed that he did not, in fact, have an additional Y chromosome.

While a number of studies have subsequently been carried out in this area the majority or the research has suggested that this is a theory with little or no substance. In their study Sarbin and Miller concluded that “studies done this far are largely in agreement and demonstrate rather conclusively that males of the XYY type are not particularly aggressive” (Miller and Sarbin, 1970, p.199).

Genetic Causes:

Family studies have been the focus of criticism but research carried out by Brunner and colleagues has made a considerable contribution to the research in this area. Despite the relatively unsuccessful investigation into the role of chromosomes as a possible cause of criminal behaviour, in the 1990s Brunner and his colleagues claimed that they had uncovered a specific gene which was linked to criminal behaviour. They engaged in an extensive study of what was termed “the Netherland’s most dysfunctional family”. The male members of the family in question seemed to be unable to control their violent tendencies and were frequently arrested. Tracing the family back for five generations, Brunner et al. found fourteen men whom he said were predisposed to criminality, including violence towards members of their own family who were female.

Brunner and his colleagues suggested that because men have only one X chromosome they are especially vulnerable to any defective gene. After a decade of intensive research the scientists claimed that they had isolated this defective gene. The gene, they said is the one which is responsible for production of the enzyme “monoamine oxidase A”, which is involved in the process by which signals are transmitted in the brain. Specifically it breaks down serotonin and noradrenaline which, when found in excess, have been linked to aggressive behaviour in humans. Since men with the mutated gene identified by Brunner and his colleagues do not produce the enzyme necessary to break down chemical transmitters, researchers suggested that they were overwhelmed by stimuli in the brain, a situation that causes uncontrollable urges and leads them into criminal behaviour (Schmalleger, 1996, p.182). While the authors accepted the fact that their research had not been replicated in any other studies, they did suggest that this was an area for future research, suggesting as it did, that genetics play an important role in criminal behaviour (Brunnet et al., 1993).

Monoamine oxidase has been linked with other neurochemicals which may be linked to criminal and antisocial behaviour (Jones 2005). Eysenck’s personality theory has been used to measure possible factors of personality which may be influential in the commission of crime. Suggesting that within the criminal fraternity different types of crimes are related to different personality patterns (Eysenck, 2003, p.93) Eysenck has pointed out that it is connected to norepinephrine, epinephrine and dopamine, all of which have been linked with personality traits important in psychosis Eysenck, 1996).

Biochemical Factors:

An increasing awareness of the physiology of the human brain, coupled with more sophisticated techniques, is leading modern criminologists to investigate the effects that certain biochemicals have on behaviour. If it were to be established that certain chemical imbalances were responsible for certain types of criminal behaviour, then this would lend weight to the theory that certain behaviours are indeed not within the control of an individual.

The Effect of Serotonin:

Current research centres on the role of neurotransmitters, chemicals in the brain which are fundamentally important to all human behaviour. There has been considerable research in respect of serotonin levels and the role this plays in criminal behaviour, where it has been identified as an important element. Serotonin has been shown, in both animal and human studies, to be an inhibitor of aggression, so low levels of serotonin have been linked to violence and suicide in humans (Williams, 2004, p.152). Raine found that individuals who were prone to anti social behaviour had lower than normal levels of serotonin in their brains (Raine, 1993), a relationship also found in research carried out by Virkkunen and Linnoila (1993). This would appear to confirm the findings of the Dutch study described above. Serotonin has been linked to brain development and it has been suggested that a disorder in this development system could lead to an increase in levels of aggressiveness and impulsivity, suggesting that the individual in this case would not have full control over his actions.

While scientists have been able to link a number of neurotransmitters, with various sorts of anti social behaviour, the nature of the relationship is not completely understood. It is unclear whether these neurotransmitters are linked to all aggression or are linked to specific types of aggression and may lead to the commission of certain specific acts and crimes. Williams points out that the role of neurotransmitters is a classic chicken and egg situation. It is not known whether the mood produces the neurotransmitters or whether the neurotransmitters lead to changes in an individual’s mood (Williams, 2004, p.153).

Criticisms of the Biological Approaches:

Attempts to explain criminal behaviour in the context of biology and genetics have been criticised, often on the basis of methodology. Walters and White have criticised many of the studies carried out on the basis that they have been badly designed, and largely inadequate in addressing the relevant issues. In particular they highlight the following shortcomings:

  • Few biological studies have adequately explained the concept of criminology, often relying on a single arrest as an indicator of criminal tendencies;
  • Twin studies, in particular, have often been inaccurate in identification of monozygotic and dizygotic twins;
  • Biological data has often been based on interviews with individuals which is subjective in its nature and therefore open to a range of interpretations;
  • Methodological problems are common including small sample sizes, lack of control groups and the use of inappropriate data analysis techniques;
  • Results have not shown consistency from country to country.

(Walters and White, 1989).

Personality Disorders:

The term “personality” is used to describe an individual’s temperamental and emotional attributes that are relatively consistent and will influence behaviour (Jones, 2006, p.398). In recent years there has been an increasing focus on individual personality traits, persistent or stable personality characteristics, and disorders and this focus has been seen as extremely useful in predicting future criminal behaviour. Theories talk about a criminal personality in which it is assumed that individuals possess definable and dominant sets of rules which determine how they will behave in virtually any situation (Williams, 2004, p.178). Many tests of personality have been developed by psychologists over the years in order to test the theory that those who have criminal tendencies have personalities which are different from those of the normal population. Many of the personality disorders which manifest themselves are initially evidenced in childhood. If it were indeed to be the case that these are predictive of later criminal behaviour, intervention with children displaying personality disorders may be a useful preventative measure.

Holmes and colleagues have identified three personality disorders which can be diagnosed in childhood and have been shown to be predictive of later behaviour:

  • Oppositional Defiance Disorder – characterised by argumentativeness and non-compliance. As these children become older their behaviour often changes for the worse, with them often starting to engage in petty crime and displaying aggression to their peers and others;
  • Attention Deficit Hyperactivity Disorder – children with this disorder are unable to stay focused on any one task for anything but a short period of time. These children are unable to analyse the consequences of their behaviour, cannot easily see things from another’s point of view and are generally unable to learn from their previous behaviour;
  • Conduct Disorder – children diagnosed with this disorder are already at the stage where they have begun to break society’s rules. This is the most severe of the three personality disorders as diagnosed in childhood and is often predictive of the development of Anti Social Personality Disorder, a disorder which can only be diagnosed when an individual is aged eighteen, and at which point they have travelled quite far down the road of anti social behaviour and not conforming with the norms in society.

(Holmes et al., 2001).

With a clear link established between these early childhood disorders and future criminal behaviours, early diagnosis and effective interventions are vital in this area. Tests for determining an individual’s personality and the likelihood for future criminal behaviour have come under considerable scrutiny. The tests themselves have developed considerably in their complexity and the sophistication of their methodology but a study by Arbuthnot and colleagues stated that the doubtful validity of much of the research that had gone on in this area prevented their coming to the conclusion that there was a link between personality and criminal behaviour (Arbuthnot et al., 1987).

Problems in respect of personality theories have mainly concerned the way in which personality has been measured, usually on some numerical scale. Personality tests are also problematic in that they require objective attitudes in respect of what constitutes normal. Inherent in the use of personality tests is that those who commit crimes and go against the norm must have something different from that which is viewed as normal.

The personality theories that have found the most application in the context of criminality are psychoanalytic explanations and the learning theories. There is some evidence that personality difficulties displayed in childhood are highly predictive of later criminal behaviour and can be inherited. Personality theories have not really seen much application in the predictive context, having been used mainly in respect of treatment after an offence has been committed. The rationale behind using personality tests is that behaviour can be changed by behaviour modification techniques.

Criticisms of Personality Theories:

Personality theories generally assume that all individuals have a core personality which explain how they will react to a wide variety of stimuli and whether they are likely to become criminal. They take little account of the fact that these could be changed through interventionist or environmental factors.

Environmental Influences:

Criticisms have been levelled at the approach which considers genetics as being the dominant factor in criminal behaviour, often because the methodology of the research conducted has been questioned. One such study was that carried out in Denmark in 1977 by Christainsen who reported that identical twins inherited some common characteristics that increased the likelihood of their becoming involved in criminal behaviour (Crristiansen, 1977). The criticisms levelled at this and other similar research is the fact that twins may share higher than average levels of shared experiences, thereby making it difficult to isolate the genetic component as a causal factor in such studies.

The first real attempts to consider crime in the context of where criminal lived, and their associated environment, took place in the 1820s in France and Belgium. These studies were pioneered by Adolphe Quetlet and Andre-Michel Guerry who collected data about the areas in which criminals lived, and in so doing began a field of research that would continue throughout Europe for a long time to come, eventually being adopted by American and global researchers also.

Modern Environmental Criminology:

It has been suggested that the impact of the environment on behaviour reduces with age. While adults are able to exercise some choice as to their environment, children have no such choice, so the impact of the environment in more profound (Jones, 2005). Reluctance to consider genetic factors as instrumental in criminal conduct has had political overtones (Haller, 1968), as it suggests a somewhat depressing prognosis for individuals born with the genetic predisposition to become criminals. The idea that there as an inextricable link between crime and the environment has been considered as an alternative and really came to the fore in the UK in the 1970s, with crime figures beginning to rise sharply, and crime being increasingly attributed to young, disaffected males living in areas of social deprivation (Jones, 2006, p.134).

Situational Crime Theory:

The ideas surrounding environmental criminology have had a considerable impact on public policy in the UK. The Home Office Research Unit was set up in the 1950s and began to work on what it called situational crime prevention, an attempt to reduce the opportunities to commit crime. This approach does not see crime as the result of any physiological or biological impulses but sees it as more opportunity driven which causes individuals to make choices in the context of these situational factors (Jones, 2006, p.138). Situational crime theory does not focus on career criminals who will find their own opportunities to commit crime, but seeks to address the problem of those who may not have been involved in the criminal justice system before. In the context of this theory the key factor is opportunity and the exercise of free will, and proponents of this approach argue that a reduction in opportunities will, in turn, lead to a reduction in the commission of crime.

Situational crime theory has its critics who suggest that the theory focuses too greatly on the crime at the expense of focusing on the type of persons involved in the commission of crimes. Tonry has argued that it is likely to increases the fear of crime among the general public (Tonry, 2004). Despite criticisms, recent research carried out in London has added weight to the idea that there may indeed be a causal link between deprivation, crime and a particular area, when a study by Dorling and colleagues in 2001 suggested that patterns of social deprivation in London have changed very little since the turn of the nineteenth century (Dorling et al., 2001).

Crime and Poverty:

Because large numbers of crimes are committed by people who have very little money, there has long been a school of thought that there is a causal link between crime and poverty. This is a view which has been held for many years and was first investigated in France by Guerry who found that in the more affluent areas there were higher rates of crime against property while in the poorer areas there were higher incidences of violent crime. There were poor people living in the more affluent areas and Guerry concluded that it was not poverty per se that caused higher rates of crime but the fact that there was more opportunity in the wealthier areas for crime against property. Recent research as been inconclusive regarding the role played in criminal activity by poverty. What does appear to be clear is that there is no direct link between crime and poverty as an isolated factor as there are, for example, many tribes who are materially very poor but did not engage in high levels of criminal activity (Williams, 2004, p.286).

Research has suggested that poverty only becomes a factor in criminal activity when there is a large degree of social inequality, a large gap between the “haves” and the “have-nots”. This leads to the suggestion that if, in the population as a whole, there was a degree of poverty, this would not lead to higher rates of crime. This has been coupled with the suggestion that it is not even the inequality which is the causal factor but the perception that this is unfair which leads to higher levels of criminal activity (Stack, 1984). Recent theories have investigated the link between crime and inequality and it has been suggested by Vold and his colleagues, who refer to a number of studies, that there is a link between inequality and violent crime including homicide (Vold et al., 2002).


In terms of environmental factors, none is more important or exerts such an influence in shaping an individual as the family in which he grows up. Famil

Bill Carlson

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