When crime is truly the product of rational choice, the offender commits the act for reasons of personal gain or gratification. His or her behavior is under his or her complete control. How and to what degree, however, might other factors intrude on and compromise his or her ability to exercise free will? The response to this question has come in the form of innumerable theories, each purporting to explain criminal behavior in terms of specific factors. Broadly speaking, criminal behavior theories involve three categories of factors: psychological, biological, and social. In fact, human behavior is the product of complex interactions among many factors. Rather than providing a summary of myriad theories, this research paper focuses on the main factors involved in the expression and suppression of criminal behaviors.
There is a vast criminological literature that identifies a wide range of environmental factors as causally linked to criminal behavior. These include developmental, social, and economic factors. For example, poverty is often cited as a socioeconomic condition linked to crime. The stress, strain, and frustration experienced by those lacking the financial resources to meet their needs and fulfill their desires through legitimate means renders them more inclined to commit crime than affluent individuals with ready access to legitimate means. Poor nutrition is an especially troubling aspect of poverty. Nutritional deficiencies can result in or exacerbate problems such as learning disabilities and poor impulse control. Such cognitive dysfunctions have been identified as precursors to delinquency and adult criminality. Thus, one’s position in the social structure of society—as operationalized by variables such as level of income—can be a significant contributing factor in the criminal activities of some individuals by virtue of its impact on brain function.
Growing up in a household where parental displays of violence are commonplace can shape the behavior of children so as to make them more likely to respond to their own problems with violent means. While aggression and violence are not synonymous, that they are correlated is undeniable. Psychologist Albert Bandura demonstrated the importance of social learning in the development of aggressive behavior. Exposure to a violent role model may operate as a trigger of preexisting psychological and biological factors that predispose that individual to aggressive behavior. This may explain why only one of the two sons whose father assaults their mother grows up to beat his own wife—there were additional factors that rendered him more readily influenced by the violent model; or, conversely, the nonviolent son was resistant to the influence by virtue of individual “protective” factors, such as high IQ.
There is a substantial literature on a “cycle of violence” whereby victims of childhood abuse and neglect are predisposed to engage in violent behavior in adulthood, thus passing the violence from one generation to the next. Other research has examined the effects of being bullied during formative years, finding that the victims in turn become victimizers. In animal experiments, exposure to conditions of inescapable threat has been found to alter specific chemicals in the brain involved in aggression and the inhibition of aggression, with the result that formerly docile animals go on to display inappropriate and excessive aggression, attacking smaller, weaker animals whenever presented with them. In essence, they become the “playground bully.” Thus, a change in the environment—exposure to inescapable threat— leads to changes in biology, which lead to the changes in behavior. Empirical studies on the effects of child maltreatment reveal that in addition to psychological problems actual structural and functional damage to the developing brain may occur. These neurobiological effects may be an adaptive mechanism for living in that dangerous environment. Regardless, they also tend to predispose the individual to a range of psychiatric conditions, aggressive behaviors, and stress-related illnesses. Resilient children, so called because of their ability to thrive under high-risk conditions, appear to have cognitive capabilities (notably higher verbal intelligence) that enable them to adapt to their stressful environment. Understanding the mechanisms that underlie resilience may reveal deficits in those who succumb to the harmful effects of their disadvantaged or abusive childhood—often becoming delinquent and criminal as a result.
Of course, the majority of poor people are not criminals, and the majority of those growing up in abusive homes or who are bullied do not go on to become criminals, raising the question: What it is about those who commit crime that distinguishes them from others who experience similar circumstances but are law abiding? Furthermore, why would individuals who do not experience such adversity commit crime? The answer to these questions is that social factors affect different people differently. By and large it is the psychological and biological makeup of an individual that determines how and to what extent external forces affect his behavior. Psychological and biological factors interact to render an individual more or less vulnerable to adverse social conditions. This should not be taken to diminish the influence of social factors on criminal behavior, for indeed they have a significant role, but rather to highlight the fact that the effect they have depends on the psychological and biological makeup of the individual. Ultimately, it is the individual who acts—criminally or otherwise.
By virtue of the requirement of mens rea, criminal courts are concerned with the psychological elements that underlie criminal behavior. Research teaches, however, that the psychology of the offender emanates from a biological substrate. And, one’s psychological states affect various aspects of his or her biology. Mind and brain have an indelible connection. An individual’s psychological state or mental status—whether at the scene of a crime or in a courtroom—involves biological mechanisms.
Psychopathology—the study of diseases/disorders of the mind—constitutes a major area of preparation for the forensic psychologist. While the vast majority of individuals with mental disorder do not commit crimes, it is estimated that rates of serious mental disorder among prison inmates are three to four times greater than they are for members of the general pop-ulation. Although this cannot blindly be taken to mean that the crimes of mentally disordered inmates were due to their psychopathology, or that mental disorder predated their incarceration, their disproportionate numbers relative to the general population nonetheless confer significance to mental disorder as a contributing factor in criminal behavior.
The relationship between criminal behavior and mental disorder is complex. Individuals who experience false perceptions (i.e., have hallucinations such as hearing voices that have no basis in objective reality) and/or hold false beliefs (i.e., have delusions such as “people are out to kill me”) are considered to have a major mental disorder, or psychosis. Recent research has linked schizophrenia, a psychosis, to an increased risk of committing violent crime—usually against significant others in their lives (not the randomly encountered strangers portrayed in popular media). While it is understandable how someone who is out of touch with reality can harm another as a result (e.g., by having a delusion that he has a divine mission to cleanse the streets of vermin—say, by killing homeless people), the majority of psychotic individuals do not commit crimes.
Research on hallucinations in schizophrenics reveals that the basis for their false perceptions is brain dysfunction. For example, the occurrence of auditory hallucinations coincides with the firing of neurons in brain regions normally involved in processing sound— but in this case in the absence of sound. Instead of asking the nebulous question, “Why does a schizophrenic hear voices?” we are now positioned to ask why neurons in particular regions of the brain misfire in the absence of external stimuli. Thus, the impetus for violence in a schizophrenic individual—when he attacks because the voices say the other person intends harm—appears to arise out of aberrant neural activity.
Of the mental disorders currently recognized by clinicians and researchers, most are not deemed psychoses. Rather, they are disorders of personality, impulse control, and the like. Psychopathy, a form of personality disorder, is exhibited as a cluster of specific affective, interpersonal, and socially deviant behaviors. Although psychopaths make up only about 1% of the general population, they are estimated to comprise approximately 25% of prison populations. The nature of their disorder—lacking remorse for their antisocial actions and emotional empathy for those whose rights they violate—makes them especially well suited for criminal activity. While most psychopaths are not criminal (nonetheless behaving in ways that disregard consideration for others), of those who are, recidivism rates tend to be significantly higher than for nonpsychopathic offenders.
Although psychopaths are not psychotic, the neurobiological mechanisms that normally impart emotion to cognitions, thoughts, and attitudes appear to be dysfunctional in the psychopath. The psychologist Robert Hare suggests that whereas genetic (and other biological) factors determine the aberrant personality structure, the environment may shape how the disorder is expressed as behavior. Positron emission tomography and single-photon-emission computed tomography scans have identified a number of specific regions in the brains of violent psychopaths that do not function normally. In particular, the prefrontal cortex—part of the frontal lobes of the brain largely responsible for rational decision making and impulse control—appears to be underaroused, rendering it incapable of effectively managing emotional urges. Impulsive behaviors, including crimes, are the result.
However cognitive abilities are defined, certainly they have a major role in criminal behavior. Where research has used IQ as a measure of intelligence, by and large offenders have lower scores than nonoffenders. Typically, individuals with low intellectual ability have difficulty delaying gratification, curbing their impulses, and appreciating the alternative means to get what they want. With substantial intellectual impairment, they tend to be less inhibited from doing harm because they lack the appreciation for the wrongfulness of their conduct. Although environment can facilitate or suppress the development and expression of one’s cognitive abilities, research indicates that these have a substantial heritable component.
The concept of emotional intelligence holds considerable promise for a more comprehensive understanding of chronic criminality. Those with low emotional intelligence—people who lack insight into their own behavior and empathy toward others—are less inhibited about violating the rights of others. Injury to the (ventromedial) prefrontal cortex has been linked to the onset of reckless and antisocial behavior (including violence) without remorse, suggesting our moral compass is rooted in specific frontal lobe functions that for the chronic offender are defective.
Much neglected in the mainstream literature on criminal behavior are the effects of traumatic events in early childhood from a psychoanalytic perspective. Twenty-first century technology provides for—should we choose—a recasting of Freudian constructs as specific neurobiological factors. The id, responsible for generating unconscious and primitive urges, may correspond with the limbic system—which includes brain structures involved in basic emotions, motivation, and memory. The aspect of the personality Sigmund Freud referred to as the ego mediates the self-centered demands of the id. The ego develops in childhood and grounds the individual in reality. It would be this rational aspect of personality that negotiates with the emotional and impulsive id. Read frontal lobes here. As for Freud’s superego, the moral aspect of personality may well “reside,” at least partially, in the ventromedial pre-frontal cortex. Remorseless antisocial behavior follows damage to this area of the brain. Reconceptualizing Freudian constructs in this manner need not negate their validity, for the basic tenet—relating defects of personality to early trauma—remains intact. Rather, a neurobiological interpretation of psychoanalytic processes affords them something they heretofore lacked—the ability to be empirically validated.
While we refer to disordered mental states or diseased mind, frequently understated or unstated are the neurobiological processes that underlie them. Whatever the psychological problem, we can no longer speak of the psychological factors associated with criminal behavior without also discussing biological factors— virtually in the same sentence.
The numerous and varied social and psychological factors that increase the risk of criminal behavior are mediated by biological processes.
Proper diet is essential to optimal brain function. For example, complex carbohydrates are broken down to make glucose—the basic fuel for the brain. Many nutrients are involved in converting that glucose into energy. A deficiency in any one of these essential nutrients com-promises brain function by lowering the available energy. The frontal lobes of the brain, responsible for rational thinking, organizing behavior, and moderating emotional impulses, require approximately twice the energy as the more primitive regions. If energy levels are depleted, higher functions become impaired leaving lower brain activity uninhibited. Effectively, our emotions will have their way with us. Beyond basic energy needs, specific nutrients are required for the synthesis of neurotransmitters. It is, therefore, understandable how malnutrition compromises cognitive function and, in so doing, facilitates antisocial and aggressive behaviors.
Of the diagnosed illnesses associated with violent behavior, substance abuse ranks highest. The disinhibiting effects of alcohol are evident in police reports—replete as they are with accounts of domestic violence, aggravated assault, murder, and rape under its influence. Substance abuse has a particularly deleterious effect on individuals with preexisting mental disorder, exacerbating their dysfunction. It is not that alcohol causes violent behavior; rather, it appears to trigger violence in those already prone to behave violently by virtue of other factors.
Exposure to toxic agents in the environment such as pesticides and lead can delay or impair an individual’s intellectual development and thus affect behavior and its regulation. In this regard, teratogens—factors that interfere with normal embryonic development—have a particularly important role in predisposing some individuals to a life of crime. The legacy of cognitive deficits and behavioral sequelae due to, for example, prenatal exposure to drugs and alcohol, are well documented in the literature.
Neurotransmitters are responsible for conducting electrochemical impulses within and across regions of the brain (as well as throughout the body). Many psychiatric disorders have been linked to imbalances in neurotransmitter systems. Serotonin is involved in a number of brain functions, including regulation of emotional states. In laboratory experiments, lowering the serotonin levels results in the onset of impulsive and aggressive behavior. That abuse and neglect in childhood can result in permanently reduced levels of serotonin is therefore an important observation for our understanding of the etiology of violence.
Hormones function in much the same way as neurotransmitters except they are released into the bloodstream rather than between neurons. Abnormally high levels of circulating testosterone—a sex hormone associated with the drive to dominate and compete— have been linked to excessive aggression. The phenomenon of “roid rage” in body builders who use anabolic steroids and exhibit extreme and uncontrollable violence attests to this effect. Such observations, as well as research on stress hormones correlating, for example, low levels of salivary cortisol with severe and persistent aggression, show the importance of hormonal contributions to criminal behavior.
Research on skin conductance, heart rate, and brainwave activity has linked low arousal to criminal behavior. In fact, in young children, these psychophysiological conditions have been reported to portend later delinquency with a high degree of accuracy. What these and the aforementioned studies suggest is that the brains of chronic offenders work differently. As we proceed to identify more of the factors linked to criminal behavior, we will take with us one particular question, the answer to which will have implications that at once generate fear and optimism: To what extent are the factors genetically determined?
A variety of methodologies—examining twins and adoptees, chromosomal abnormalities, and DNA polymorphisms—have been applied to evaluate the role of genetic factors in criminal behavior and aggression. Although it is not anticipated that a “crime gene” will ever be discovered, it is clear there are genes that code for specific neurochemicals linked to different kinds of behavior. To illustrate, a specific—albeit rare—mutation has been identified in a gene that holds the recipe for a particular enzyme known to affect the level of certain neurotransmitters in the brain. This defect has been linked to a propensity toward impulsive and excessive aggression and violence in each of the men of the family who has this mutation.
Studies in behavioral genetics support the contention that aggressive behavior is moderately heritable. Aggressive behaviors confer advantage to the males of a species as they compete for territory and access to females. Evolutionary psychology holds that aggressive traits that increase reproductive success will be selected and carried across successive generations. Primatologist Ronald Nadler contends that sexual aggression is inherent in the behavioral repertoires of great apes—animals that are among our closest biological affiliates. Human males, as a function of their drive to procreate, would be naturally inclined to have sex with as many different partners as possible, maximizing the probability that the species will survive and also that their own genes will be transmitted to the next generation. The fact that most males do not rape is in large measure due to their socialization; rapists are males who have not been effectively socialized in this regard. We can appreciate through this example how specific psychosocial risk factors (e.g., low intelligence) can increase the probability of criminal and violent behavior—in this case, rape.
The long tradition of assuming crime to be the product of volition, unencumbered by aberrant psychological or biological processes, is under attack. In the end, we may find it is psychologist Adrian Raine’s bold conceptualization of criminality as a clinical disorder that best fits what we learn. To embrace this position, however, would require us to revisit our notions of crime and punishment—and treatment. If criminal behavior, at least impulsive violent criminal behavior, is inherently pathological, the implications are legion. In their determinations of culpability, the courts are thus wise to proceed with caution. As behavioral science research and technology advance, it is likely that the critical mass of the data will, ultimately, persuade.
- Hare, R. D. (1993). Without conscience: The disturbing world of the psychopaths among us. New York: Pocket Books.
- Raine, A. (1993). The psychopathology of crime: Criminal behavior as a clinical disorder. New York: Academic Press.
- Salovey, P., & Mayer, J. (1990). Emotional intelligence. Imagination, Cognition, and Personality, 9(3), 185-211.
- Strueber, D., Lueck, M., & Roth, G. (2006, December). The violent brain. Scientific American, 20-27.
- Teicher, M. H. (2002, March). Scars that won’t heal: The neurobiology of child abuse. Scientific American, 68-75.
- Widom, C. S. (1989). The cycle of violence. Science, 244, 160-166.