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Winner of 2005 RIT Kearse Award for Writing

Genetic and Environmental Influences on Criminal Behavior

Caitlin M. Jones
Rochester Institute of Technology

Criminal behavior has always been a focus for psychologists due to the age old debate between nature and nurture. Is it the responsibility of an individual's genetic makeup that makes them a criminal or is it the environment in which they are raised that determines their outcome? Research has been conducted regarding this debate which has resulted in a conclusion that both genes and environment do play a role in the criminality of an individual. This evidence has been generated from a number of twin, family, and adoption studies as well as laboratory experiments. Furthermore, the research has stated that it is more often an interaction between genes and the environment that predicts criminal behavior. Having a genetic predisposition for criminal behavior does not determine the actions of an individual, but if they are exposed to the right environment, then their chances are greater for engaging in criminal or anti-social behavior. Therefore, this paper will examine the different functions that genetics and the environment play in the criminal behavior of individuals.

There is a vast amount of evidence that shows our criminal justice system is the new home for individuals with psychological problems. Although this may seem like a solution to some, it is creating a dilemma for our society. Once we label these individuals as criminals it creates a stigma for those who may suffer from psychological problems. Certain psychological problems have been shown to be heritable and if given the right circumstances, individuals with those genes could find themselves engaging in criminal activity. Therefore, should society look towards limiting the reproductive capabilities of individuals who suffer from certain psychological problems to better society?

That same question was asked back in the late nineteenth and early twentieth centuries when the role of genetics in crime was widely accepted (Joseph, 2001). Prominent researchers believed that genes were fully responsible for criminal activity and that criminals could be identified by their physiological features. Along with this information and the idea of a eugenics movement during the same time period, it was not surprising to learn that acts of sterilization took place to rid society of “criminals, idiots, imbeciles, and rapists" (Joseph, 2001, p. 182). This period was therefore marked with inhumane treatment and the belief that genes were the sole reason behind criminal behavior.

Not long after the practices of controlled breeding, there was evidence to support the idea that the environment also played an important role in crime. Early family studies were conducted that showed a predisposition for criminal behavior as a result of inherited characteristics, but that an individual's characteristics and personality could still be modified by the environment (Joseph, 2001). Although these studies were void of high validity and reliability, it still raised the question of whether the environment can also influence individuals to act in a criminal manner. The debate between genetics and environment continues today with much more reliable research and data. Consequently, this paper will examine the various roles in which both genes and environmental factors influence criminal behavior.

Definition and Measurement of Criminal Behavior

To fully understand the nature of how genes and the environment influence criminal behavior, one must first know how criminal behavior is defined. Law in our society is defined by social and legal institutions, not in biology (Morley & Hall, 2003). Therefore determining what constitutes criminal behavior can envelope a wide variety of activities and for that reason, researchers tend to focus on the wider context of antisocial behavior. Authors Morley and Hall (2003), who have investigated the genetic influences on criminal behavior, point out three different ways to define antisocial behavior. First is equating it with criminality and delinquency, which both involve engaging in criminal acts. Criminality can lead to arrest, conviction, or incarceration for adults, while delinquency is related to juveniles committing unlawful acts (Rhee & Waldman, 2002). Information can be collected using court and criminal records, as well as self report surveys to analyze the influences that were present. Secondly, they advise individuals to define antisocial behavior is through criteria used to diagnose certain personality disorders. More specifically, they mean those personality disorders, such as Antisocial Personality Disorder, which is associated with an increased risk in criminal activity. A final measure suggested for defining antisocial behavior is by examining personality traits that may be influential in the criminal behavior of individuals. Traits such as aggressiveness and impulsivity are two traits that have been investigated the most (Morley & Hall, 2003). Further details of disorders and personality traits associated with criminal behavior will be discussed later in the paper.

With regards to determining the effects the environment plays in criminal behavior there are fewer resources available. Observational studies and reports submitted by parents are two sources, but not everyone agrees on the validity of information collected from these sources. Three additional sources that most researchers cite when gathering information about both genetic and environmental influences are twin, family, and adoption studies (Tehrani & Mednick, 2000).

Twin, Adoption, and Family Studies

There has been great debate between researchers regarding the outcomes of twin, adoption, and family studies. Some claim that these studies support the notion of a genetic basis to criminal behavior (Tehrani & Mednick, 2000). On the other hand, some have concluded that there is not enough evidence from these twin, family, and adoption studies to profess that genetics do play a role in antisocial or criminal behavior (Lowenstein, 2003). To understand why there are such conflicting opinions, one must first look at the available studies that have been conducted.

Twin studies are conducted on the basis of comparing monozygotic (MZ) or identical twins and their rates of criminal behavior with the rates of criminal behavior of dizygotic (DZ) or fraternal twins. Ordinarily these studies are used to assess the roles of genetic and environmental influences. If the outcomes of these twin studies show that there is a higher concordance rate for MZ twins than for DZ twins in criminal behavior, then it can be assumed that there is a genetic influence (Tehrani & Mednick, 2000). A study conducted looked at thirty two MZ twins reared apart, who had been adopted by a non-relative a short time after birth. The results showed that for both childhood and adult antisocial behavior, there was a high degree of heritability involved (Joseph, 2001). This study was of particular importance because it examined the factor of separate environments. Another researcher studied eighty-five MZ and one hundred and forty-seven DZ pairs and found that there was a higher concordance rate for the MZ pairs. Ten years later after checking police records of these same twins, two other researchers concluded that there was a fifty-four percent heritability of liability to crime (Joseph, 2001). Around the same time of the study just mentioned, two researchers studied forty-nine MZ and eighty-nine DZ pairs, but found no difference in the concordance rates. They concluded therefore that in respect to common crime, hereditary factors are of little significance (Joseph, 2001). Many other twin studies have been conducted, but there is concern over the validity of those studies and their ability to separate out the nature and nurture aspects; therefore other sources of information should be examined.

Adoption studies are critical in examining the relationship that exists between adopted children and both their biological and adoptive parents because they assume to separate nature and nurture. Studies have been conducted that test for the criminal behavior of the adopted-away children, if their biological parents had also been involved with criminal activity. In Iowa, the first adoption study was conducted that looked at the genetics of criminal behavior. The researchers found that as compared to the control group, the adopted individuals, which were born to incarcerated female offenders, had a higher rate of criminal convictions as adults. Therefore this evidence supports the existence of a heritable component to antisocial or criminal behavior (Tehrani & Mednick, 2000). Another study in Sweden also showed that if a biological background existed for criminality, then there was an increased risk of criminal behavior in the adopted children. In Denmark, one of the largest studies of adopted children was conducted and found similar results to the previous studies. The defining feature of the Denmark study was that the researchers found a biological component for criminal acts against property, but not for violent crimes (Joseph, 2001). Children whose biological fathers had been convicted of property crimes were more likely to engage in similar behavior, when compared to those biological fathers who had been convicted of violent crimes. According to an article by Jay Joseph (2001), who studied all of the minor and major adoption studies, the majority of researchers have found and agreed upon the non-significance of genes in violent crime. This reestablishes the findings from the studies mentioned already in that there may be a genetic component to antisocial behavior or that genes influence criminal behavior, but specifically for property offenses.

Family studies are the third type of instrument used to assess the relationship between genetics and environmental influences on criminal or antisocial behavior. Research in this field has probably been the least accepted by psychologists and other scholars because of the degree of difficulty in separating out nature and nurture in the family environment. Children experience both the influence of their parents' genes and also the environment in which they are raised, so it is difficult to assign which behaviors were influenced by the two factors. Twin studies have this flaw, as stated earlier, but it is more prevalent in family studies. An additional concern with family studies is the inability to replicate the results, therefore leading to a small number of studies. Regardless of these drawbacks, one family study in particular should be acknowledged for its findings.

Brunner, Nelen, Breakefield, Ropers, and van Oost (1993) conducted a study utilizing a large Dutch family. In their study they found a point mutation in the structural gene for monoamine oxidase A (MAOA), a neurochemical in the brain, which they associated with aggressive criminal behavior among a number of males in that family (Alper, 1995). These males were reported to have selective MAOA deficiency, which can lead to decreased concentrations of 5-hydroxyindole-3-acetic acid (5-HIAA) in cerebrospinal fluid. Evidence suggests that low concentrations of 5-HIAA can be associated with impulsive aggression. These results have not been confirmed in any additional family studies, which lead to a need for more studies to determine if other families share similar results (Brunner et al., 1993). However, this one family study does seem to suggest that genetics play an important role in antisocial or criminal behavior.

Neurochemicals in Criminal and Anti-Social Behavior

Neurochemicals are responsible for the activation of behavioral patterns and tendencies in specific areas of the brain (Elliot, 2000). As seen in the Brunner et al. study, there have been attempts to determine the role of neurochemicals in influencing criminal or antisocial behavior. Included in the list of neurochemicals already cited by researchers are monoamine oxidase (MOA), epinephrine, norepinephrine, serotonin, and dopamine.

Monoamine oxidase (MAO) is an enzyme that has been shown to be related to antisocial behavior. Specifically, low MAO activity results in disinhibition which can lead to impulsivity and aggression (Elliot, 2000). The Brunner et al. study is the only one to report findings of a relationship between a point mutation in the structural gene for MAOA and aggression, which makes the findings rare. However, there has been other evidence that points to the conclusion that deficiencies in MAOA activity may be more common and as a result may predispose individuals to antisocial or aggressive behavior (Brunner et al., 1993). MAO is associated with many of the neurochemicals that already have a link to antisocial or criminal behavior. Norepinephrine, serotonin, and dopamine are metabolized by both MAOA and MAOB (Elliot, 2000). While, according to Eysenck (1996), MAO is related to norepinephrine, epinephrine, and dopamine, which are all related to the personality factor of psychosis.

Serotonin is a neurochemical that plays an important role in the personality traits of depression, anxiety, and bipolar disorder (Larsen & Buss, 2005). It is also involved with brain development and a disorder in this system could lead to an increase in aggressiveness and impulsivity (Morley & Hall, 2003). As Lowenstein (2003) states, “studies point to serotonin as one of the most important central neuro-transmitters underlying the modulation of impulsive aggression" (p.72). Low levels of serotonin have been found to be associated with impulsive behavior and emotional aggression. In addition, children who suffer from conduct disorder (which will be discussed later), have also been shown to have low blood serotonin (Elliot, 2000). Needless to say, there is a great deal of evidence that shows serotonin is related to aggression, which can be further associated with antisocial or criminal behavior.

Dopamine is a neurotransmitter in the brain that is associated with pleasure and is also one of the neurotransmitters that is chiefly associated with aggression. Activation of both affective (emotionally driven) and predatory aggression is accomplished by dopamine (Elliot, 2000). Genes in the dopaminergic pathway have also been found to be involved with Attention Deficit Hyperactivity Disorder (ADHD) (Morley & Hall, 2003). In one study cited by Morley and Hall (2003), a relationship was found between the genes in the dopaminergic pathway, impulsivity, ADHD, and violent offenders. Obviously, from this list of neurochemicals it seems plausible that there is a genetic component to antisocial or criminal behavior.

Personality Disorders and Traits

Personality traits and disorders have recently become essential in the diagnosis of individuals with antisocial or criminal behavior. These traits and disorders do not first become evident when an individual is an adult, rather these can be seen in children. For that reason it seems logical to discuss those personality disorders that first appear in childhood. Attention Deficit Hyperactivity Disorder (ADHD), Conduct Disorder (CD), and Oppositional Defiance Disorder (ODD) are three of the more prominent disorders that have been shown to have a relationship with later adult behavior (Holmes, Slaughter, & Kashani, 2001).

ODD is characterized by argumentativeness, noncompliance, and irritability, which can be found in early childhood (Holmes et al., 2001). When a child with ODD grows older, the characteristics of their behavior also change and more often for the worse. They start to lie and steal, engage in vandalism, substance abuse, and show aggression towards peers (Holmes et al., 2001). Frequently ODD is the first disorder that is identified in children and if sustained can lead to the diagnosis of CD (Morley & Hall, 2003). It is important to note however that not all children who are diagnosed with ODD will develop CD.

ADHD is associated with hyperactivity-impulsivity and the inability to keep attention focused on one thing (Morley & Hall, 2003). Holmes et al. (2001) state that, “impulse control dysfunction and the presence of hyperactivity and inattention are the most highly related predisposing factors for presentation of antisocial behavior" (p.184). They also point to the fact that children diagnosed with ADHD have the inability to analyze and anticipate consequences or learn from their past behavior. Children with this disorder are at risk of developing ODD and CD, unless the child is only diagnosed with Attention Deficit Disorder (ADD), in which case their chances of developing ODD or CD are limited. The future for some children is made worse when ADHD and CD are co-occurring because they will be more likely to continue their antisocial tendencies into adulthood (Holmes et al., 2001).

Conduct Disorder is characterized with an individual's violation of societal rules and norms (Morley & Hall, 2003). As the tendencies or behaviors of those children who are diagnosed with ODD or ADHD worsen and become more prevalent, the next logical diagnosis is CD. What is even more significant is the fact that ODD, ADHD, and CD are risk factors for developing Antisocial Personality Disorder (ASPD). This disorder can only be diagnosed when an individual is over the age of eighteen and at which point an individual shows persistent disregard for the rights of others (Morley & Hall, 2003). ASPD has been shown to be associated with an increased risk of criminal activity. Therefore, it is of great importance that these early childhood disorders are correctly diagnosed and effectively treated to prevent future problems.

Another critical aspect that must be examined regarding antisocial or criminal behavior is the personality characteristics of individuals. Two of the most cited personality traits that can be shown to have an association with antisocial or criminal behavior are impulsivity and aggression (Morley & Hall, 2003). According to the article written by Holmes et al. (2001), antisocial behavior between the ages of nine and fifteen can be correlated strongly with impulsivity and that aggression in early childhood can predict antisocial acts and delinquency. One statistic shows that between seventy and ninety percent of violent offenders had been highly aggressive as young children (Holmes et al., 2001). These personality traits have, in some research, been shown to be heritable.

Environmental Influences

Thus far it has been established through research and various studies that genetics do influence criminal or antisocial behavior. Researchers agree on the point that genes influence personality traits and disorders, such as the ones just mentioned. However, researchers also agree that there is an environmental component that needs to be examined. Environmental influences such as family and peers will be discussed, as well as a look into the social learning theory.

The family environment is critical to the upbringing of a child and if problems exist then the child is most likely to suffer the consequences. We have seen the problems associated with a child who is diagnosed with ADHD and how that can influence antisocial or criminal behavior. In relation to that, some researchers have claimed that it is the family environment that influences the hyperactivity of children (Schmitz, 2003). The researchers in this article specifically identify family risk factors as poverty, education, parenting practices, and family structure. Prior research on the relationship between family environment and child behavior characterizes a child's well being with a positive and caring parent-child relationship, a stimulating home environment, and consistent disciplinary techniques (Schmitz, 2003). Families with poor communication and weak family bonds have been shown to have a correlation with children's development of aggressive/criminal behavior (Garnefski & Okma, 1996). Therefore it seems obvious to conclude that those families who are less financially sound, perhaps have more children, and who are unable to consistently punish their children will have a greater likelihood of promoting an environment that will influence antisocial or delinquent behavior. Another indicator of future antisocial or criminal behavior is that of abuse or neglect in childhood. A statistic shows that children are at a fifty percent greater risk of engaging in criminal acts, if they were neglected or abused (Holmes et al., 2001). This has been one of the most popular arguments as to why children develop antisocial or delinquent behaviors.

One additional research finding in the debate between genetic and environmental influences on antisocial or criminal behavior has to deal with the age of the individual. Research seems consistent in recognizing that heritability influences adult behavior more than environmental influences, but that for children and adolescents the environment is the most significant factor influencing their behavior (Rhee & Waldman, 2002). As an adult, we have the ability to choose the environment in which to live and this will either positively or negatively reinforce our personality traits, such as aggressiveness. However, children and adolescents are limited to the extent of choosing an environment, which accounts for the greater influence of environmental factors in childhood behaviors.

Another significant factor in the development of antisocial or delinquent behavior in adolescence is peer groups. Garnefski and Okma (1996) state that there is a correlation between the involvement in an antisocial or delinquent peer group and problem behavior. One of the primary causes as to why this occurs can be traced back to aggressive behavior in young children. When children are in preschool and show aggressive tendencies towards their peers, they will likely be deemed as an outcast. This creates poor peer relationships and relegates those children to be with others who share similar behaviors. A relationship like this would most likely continue into adolescence and maybe even further into adulthood. The similar tendencies of these individuals create an environment in which they influence one another and push the problem towards criminal or violent behavior (Holmes et al., 2001).

Social learning theory has been cited as way to explain how the environment can influence a child's behavior. Using this theory to explain the aggressive or antisocial behavior of a child means that a child observes aggressive behavior between parents, siblings, or both. As a result, the children believes that this aggressive behavior is normal and can therefore use it themselves because they do not see the harm in acting similar to their parents (Miles & Carey, 1997). As stated earlier, interaction between family members and disciplinary techniques are influential in creating antisocial behavior. Using the social learning theory these two factors are also critical in the development of aggression. Children who are raised in an aggressive family environment would most likely be susceptible to experiencing a lack of parental monitoring, permissiveness or inconsistency in punishment, parental rejection and aggression. The exposure to such high levels of aggression and other environmental factors greatly influences and reinforces a child's behavior. A significant point that should be known however is the fact that other research has supported the notion that genetics do influence levels of aggression, which stands in opposition to the social learning theory (Miles & Carey, 1997).

Gene-Environment Interactions

There are theories, however, concerning genetic and environmental influences, which seem to suggest an interaction between the two and one such theory is the general arousal theory of criminality. Personality psychologist Eysenck created a model based on three factors known as psychoticism, extraversion, and neuroticism, or what is referred to as the PEN model (Eysenck, 1996). Psychoticism was associated with the traits of aggressive, impersonal, impulsive, cold, antisocial, and un-empathetic. Extraversion was correlated with the traits of sociable, lively, active, sensation-seeking, carefree, dominant, and assertive. Finally, neuroticism was associated with anxious, depressed, low self-esteem, irrational, moody, emotional, and tense (Eysenck, 1996). Through research and surveys, Eysenck found that these three factors could be used as predictors of criminal behavior. He believed this to be especially true of the psychoticism factor and that measuring it could predict the difference between criminals and non-criminals. Extraversion was a better predictor for young individuals, while neuroticism was a better predictor for older individuals (Eysenck, 1996). An important point about these factors and the personality traits associated with them is that most of them have already been found to be heritable (Miles & Carey, 1997).

Understanding Eysenck's original model is critical to assessing the general arousal theory of criminality, which suggests an interaction between factors. Research has shown that criminality is strongly correlated with low arousal levels in the brain. Characteristics related to low arousal levels include lack of interest, sleepiness, lack of attention, and loss of vigilance. Eysenck (1996) believed that these characteristics were similar to the personality factor of extraversion. Individuals with low arousal levels and those who are extraverts need to seek out stimulation because they do not have enough already in their brains. Therefore, the premise of the general arousal theory of criminality is that individuals inherit a nervous system that is unresponsive to low levels of stimulation and as a consequence, these individuals have to seek out the proper stimulation to increase their arousal. Under this theory, the proper stimulation includes high-risk activities associated with antisocial behavior, which consists of sexual promiscuity, substance abuse, and crime (Miles & Carey, 1997). A significant fact that must be pointed out though is that not every individual with low arousal levels or those who are extraverts will seek those high risk activities just mentioned. It takes the right environment and personality to create an individual with antisocial or criminal tendencies and that is why this theory can be considered to take into account both factors of genetic and environmental influences.


There cannot be enough possible evidence to conclude the point that genetics play the most important role in the outcome or behavior of an individual. The opposing viewpoint of environmental factors is not without its doubts either as to being the prominent factor influencing antisocial or criminal behavior of an individual. In this paper, there is more evidence supporting the genetics viewpoint, but that does not mean it is more important. With the research and studies having numerous flaws and the inability to adequately separate nature and nurture, there is still a great debate between genetic and environmental factors.

Researchers, however, have certainly come far in their progression, to the point where there is a large consensus of the fact that genes do influence behavior to a certain extent. Although not as widely publicized, it is the belief of the author that these same researchers also believe that environmental factors account for what cannot be explained by genes. Therefore it seems obvious to reach the conclusion that an individual's antisocial or criminal behavior can be the result of both their genetic background and the environment in which they were raised.

One researcher has proposed a theory relating to sociopaths and their antisocial behavior. According to the theory, a primary sociopath is lacking in moral development and does not feel socially responsible for their actions. This type of sociopath is a product of the individual's personality, physiotype, and genotype. A secondary sociopath develops in response to his or her environment because of the disadvantages of social competition. Living in an urban residence, having a low socioeconomic status, or poor social skills can lead an individual to being unsuccessful in reaching their needs in a socially desirable way, which can turn into antisocial or criminal behavior. The first type of sociopath is dependent on their genetic makeup and personality, while certain factors of the second type can also be heritable. Notwithstanding, the second type has a greater dependence on environmental factors (Miles & Carey, 1997). Perhaps from this review of both genetic and environmental factors, it seems clear to support the idea of the secondary sociopath type. An individual can inherit certain genes and when combined with the right environmental factors can lead them to engage in antisocial or criminal behavior.

Although not mentioned extensively in the text of the paper, there is a great need to try and identify those individuals, especially children, who may become susceptible to certain disorders or personality traits that can lead into antisocial, delinquent, or criminal behavior. Society should not try to imitate the era of controlled breeding, but rather focus on the treatment and rehabilitation of those individuals in need. Certain educational, environment enrichment programs have been shown to have a lasting effect on children if given by a certain age (Raine, Mellingen, Liu, Venables, & Mednick, 2003). If more of these programs could be developed, society could help prevent the future antisocial or criminal behavior of children.

Peer Commentary

Men Are Not the Only Criminals: Insights Into Criminal Behavior in Women

Lisa C. Burt
Rochester Institute of Technology

Jones addressed how both genes and environment affect the outcomes and predispositions of criminals. This paper goes into great detail on whether criminal behavior is in a person's genes or environment. Having a genetic predisposition for criminal behavior and the right environment can definitely increase the likelihood of criminal activity. Jones took criminal behavior further to describe actions relating to antisocial behavior. This identification of an antisocial personality with criminal behavior leads to the idea that criminal mischief is more prevalent in males. Although our justice system is heavily loaded with male criminals, women are still part of the criminal "world."

It has been determined that men are much more physically violent than women. A few points are essential when discussing women and violence. First, women should not be entirely eliminated from the spectrum of criminality just because of their smaller predisposition toward aggression. Second, women are just as capable as men of committing a violent act. Jones discussed how certain neurochemicals are associated with criminal behavior. These neurochemicals might be more active in men, but women can still grow up in environments in which certain tendencies are brought on.

Family environment is crucial in the development of a child's brain and personality. Genetics can only go so far, and environment works to shape a child's mind after the child has left a mother's womb. Jones discussed how poor communication and weak family bonds are correlated with the development of aggressive and criminal tendencies. She also mentioned how a financially unstable family and child abuse or neglect are associated with criminal behavior. Environment is important for a child to grow and develop into a normal, prospering adult. Without proper nurturance, guidance, and support, no child, male or female, will learn coping strategies, learn life skills, or grow up with a strong sense of right and wrong and respect other people. Whether one is male or female, growing up in an environment in which one is beaten or neglected is going to cause serious traumatic repercussions. The aggressive tendencies in males lead them to become more aggressive in adulthood, which in turn is why they are more apt to commit violent crimes. Yet women have been known to commit those same violent crimes, regardless of the prevalence relative to males--women are capable of criminal behavior. Men have committed more crimes and are known to be more violent, yet women should not be eliminated from the discussion. It has not been shown that genes or environment alone determine criminal behavior, as Jones mentioned in her paper, so there should be no reason why only men are mentioned, whether directly or by implication.

Peer Commentary

Criminal Behavior and Personality Disorders

Jeffrey C. Tatar
Rochester Institute of Technology

In addition to the research showing that the gene responsible for production of monoamine oxidase has a possible link to criminality, some evidence has also shown a possible link between other genes. One area of personality research in molecular genetics that has received a lot of attention is the trait of novelty-seeking, and novelty seeking is a personality trait often associated with criminality. Research has indicated that the single DRD4 gene may account for 10% of the genetic variance in relation to novelty-seeking (Sloan, 2000). This conclusion is highly controversial because in subsequent studies there has been both replication of the original findings, and failure to replicate in other studies. It seems most molecular genetic approaches in relating heritability of personality characteristics such as criminality to a single gene frequently suffer from failures in replication.

The author also proposed that some studies have demonstrated a genetic link between ADHD, CD, and ODD and criminality. However, there are possible alternate explanations for a greater rate of criminality for those who have suffered from these disorders that the paper failed to mention. It has been shown that people evoke certain responses from their environment. It is plausible that children suffering from these disorders are treated in a different manner than normal children due to the responses that they evoke, and it is because of these environmental differences that they are more prone to criminal behavior. Say a child suffering from ADHD is having problems in school, they may be placed in a remedial class in which there is a greater rate of delinquency. This would be a very important environment difference that could contribute greatly to future criminality. Other children may also socialize less with children with these disorders, which could plausible lead to anti-social behavior.

While it is possible that in some cases the relationship between these disorders and criminality is not direct byproduct of genes, but rather as a byproduct of the same environment. There have been studies on ADHD in relation to a multitude of environmental factors, including everything from nutrition to environmental toxins. For example, a studies have been done that indicate an increased time spent viewing television in children was related to a decreased attention span and ADHD. There have also been studies showing a relationship between television viewing and desensitization to violence, which could influence criminal behavior. I am not proposing that it is watching TV that is the major factor in these disorders, or in criminality, I am just trying to illustrate that perhaps there is some environmental factor that could influence criminality as well as disorders such as ADHD.

In addition to ADHD, CD, and ODD, other disorders have shown to influence criminality as well. Studies have shown that there is a higher occurrence of disorders such as schizophrenia, major depressive disorder, bipolar disorder, just to name a few. It is possible that having these personality disorders gives one a greater predisposition toward criminal behavior. A Swedish study found that the occurrence of major mental disorders in prisoners to be 5%, as well as a 20% occurrence of personality disorders (Rasmussen, 1999). Other studies have given different values for the occurrence, but in most cases the research agrees that there is a much higher incidence of these mental disorders in those who commit crimes.

Genetics has shown to be a major factor in the occurrence of many of these disorders. There have been studies that examine the rate of personality disorders such a schizophrenia, psychosis, and manic?depressive illness in adopted children. We can hypothesize that if adopted children are more likely to suffer from such disorders if their biological parents are or were afflicted, it would be indicative of a genetic basis for the disorder. Research done by Leonard Heston in 1960 examined children of schizophrenic mothers that were removed after birth and raised by foster parents. Out of a total of 47 children examined, Heston found that nine of them were diagnosed with sociopathic personalities and antisocial behavior, and four of the 47 children developed schizophrenia. Heston also found behavioral abnormalities in many of the other children (Eysenk, 1982). This study shows a significant increase in the rate of personality disorders in the progeny of an affected parent, in comparison to population statistics on these mood disorders. In fact, when both parents are affected by a personality disorder the rate of occurrence in their offspring is even higher.

Not only do adoption studies support a genetic basis for personality disorders that are shown to have a relation to criminality, but twin studies as well. Statistics show a high concordance between identical and non-identical twins for schizophrenia and manic depression. Analysis of the statistics clearly show the genetic basis for these disorders: For schizophrenia the concordance in identical twins was 60%, compared to only 10% in non-identical twins, and the normal frequency being 1% in northern European populations. Similarly, manic depression showed a 70% concordance between identical twins, a 15% concordance between non-identical twins, and again only a 1% frequency in the normal population (Russo & Cove, 1995). This research supports the theory that genetics play a crucial role in these personality disorders.

Peer Commentary

Criminality Is a Product of Genes and Environment

Maureen E. Wood
Rochester Institute of Technology

In considering the roles of genetics and environment on criminal behavior, or any behavior for that matter, I think the best explanation is that there is a complex interaction between one's inherited traits and the environment in which he or she lives. Although the idea of environmental influences seems rather intuitive, regardless of knowledge regarding heredity and biological factors, it is surprising that some may have considered criminal behavior to be solely a result of genetics. I propose that the debate of nature versus nurture now is not whether genetics or environment influence behavior, but how complex the interaction between these factors is.

Despite the relative lack of reliability and validity in twin, adoption, and family studies, they still provide valuable insight into the roles of heredity and environment in criminal behavior. However, it seems that most studies of this kind focus on the role of heredity in influencing behavior. It would be interesting to see whether any studies with adopted children have examined the role of environment in criminal behavior. Most adoption studies examine the correlation between criminality in the biological parents of adopted children, but what about the correlation between the children and their adopted parents who are crucial to their environment?

I agree with Jones that the influence of neurochemicals on criminal and antisocial behavior are indicative of a genetic component to such behaviors. However, I think a more complete explanation of neurochemical influences is that they reflect the complex interactions between genetics and environment. There is evidence that the expression of genes is influenced by a wide variety of environmental factors. Therefore, it is very possible that disorders relating to such chemicals as serotonin and dopamine could be caused by stressful environmental situations. If environment affects the regulation of gene expression and, in turn, the activity of neurotransmitters that modulate behavior, this kind of interaction may be a significant factor in the development of criminal and antisocial behavior.

Jones's argument regarding the extent to which environmental and genetic factors influence antisocial and criminal behavior in childhood versus adulthood seems somewhat incomplete. While it is true that adults have more control of their environment than children, I do not think that children are necessarily affected more by environment and adults are influenced more by heredity. Inherited traits provide the foundation by which people are able to learn and respond to their environment. An adult's personality is the combination of traits and learned behavior patterns that have been established throughout childhood. Thus, although it is true that adults have more control over their current environment, I believe that they are still heavily influenced by both their current environment and by past exposure to environmental factors.

The social learning theory is a good way to explain the influence of environment on antisocial behavior in children, and does not necessarily have to oppose the notion of genetic influence on behavior as well. Rather, it should be considered part of a larger theory or model that could describe how environment and genetics interact. Eysenck's general arousal theory, which suggests such an interaction, could be modified to encompass the social learning theory, providing a more complete model to explain how upbringing and inherited traits interact to influence criminal behavior.

Overall, I agree with Jones's support of the idea of the secondary sociopath type. Genetics and environmental factors are so intertwined, that it seems impossible to separate them in explaining how people are caused to engage in criminal acts. Also I agree that it is important for society as a whole to take responsibility in preventing the advent of criminal and antisocial behavior in children via programs to provide children with healthy, enriching environments. A eugenic approach to preventing antisocial behavior is immoral and impinges on human rights, but taking an active approach to ensure positive environmental influences would be appropriate.

Author Response

Criminal Behavior: Those Affected, Other Causes, and Beyond

Caitlin M. Jones
Rochester Institute of Technology

I would like to thank those who wrote peer commentaries because there is obviously a lot of information that was not covered in my paper but that should not be neglected. Overall, I think it is safe to say that the majority believe that there are both environmental and genetic influences for criminal or antisocial behavior. The information from the peer commentaries adds to this notion.

Burt discussed the inference that my paper was specifically addressing the male population as more aggressive and consequently leading to criminal or antisocial behavior. I cannot disagree with this point, because some of the studies referred to in the paper were conducted on males only, and most research points to the male sex as more aggressive. It is important to know that women can be just as criminal in their behavior, as Burt pointed out. An integral piece of information, however, is that although women commit a large part of crimes, it is usually in the form of non-violent crimes.

Tatar first addressed the fact that there are other genes that may be associated with criminality, such as the gene DRD4, which is associated with the personality trait of novelty seeking. As mentioned in my paper, there is no single gene that is responsible for criminal or antisocial behavior, so I applaud the mention of other genes. I also agree with Tatar that there are other environmental influences, such as how a child's behavior or disorder can evoke certain responses from the child's environments. I believe this to be true, and more research needs to be focused on how to treat or approach these children so that their behaviors do not develop further into antisocial or criminal behavior. A topic that was omitted from my paper, which Tatar also mentioned, was the heritability of personality disorders. This is an important topic, because some personality disorders have been associated to a higher degree with criminal or antisocial behavior.

Wood believed that there is an interaction between environmental and genetic influences on criminal or antisocial behavior. The point she brought up, with which I also agree, is how complex that interaction is. With regard to the adoption studies, my research did not go far enough to report on the findings of adoptive parents and their adopted children. I am positive that those adoption studies looked at that relation, and one of the findings that might have resulted is that the environment in which the adoptive parents raise their child has a significant influence, regardless of the genes inherited. Another point that Wood discussed was the impact that environmental influences has on children and adults. I realize that the environment in which one lives will always influence one, but the point I was making regarding children being more affected was focused on peer influences as well as parents. Children are more susceptible to peer pressure and being controlled by their parents, whereas adults have the ability to shape their own environments.


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