Biological Theories of Crime

C. Biochemical Explanations: Hormones, Neurotransmitters, Diet

Another biological explanation for criminal behavior involves the body’s hormones, released by some of the body’s cells or organs to regulate activity in other cells or organs. Androgens are hormones associated with masculine traits, and estrogens are associated with feminine traits. Progesterone is another hormone associated primarily with female reproductive processes, such as pregnancy and menstruation.

1. Testosterone

Testosterone is considered the male sex hormone. Although persons of both sexes secrete testosterone, males secrete it in higher levels. Researchers have found that higher levels of this hormone are associated with increased levels of violence and aggression, both in males and females. Criminal samples have been found to have higher testosterone levels when compared with noncriminal samples, although these levels were still within normal limits.

Problems with attempting to explain criminal behavior by testosterone levels, however, are problematic. Testosterone levels naturally fluctuate throughout the day and in response to various environmental stimuli. For example, levels among athletes increase prior to competitions, perhaps indicating that testosterone is produced to increase aggression instead of as a response to aggression. This makes correlating levels to behavior and controlling for environmental stimuli extremely difficult.

Recent research conducted by Ellis in 2003, however, has added an evolutionary component. In his evolutionary neuroandrogenic theory, Ellis argued that increased levels of testosterone reduce the brain’s sensitivity to environmental stimuli, making a person act out, with reduced abilities to control emotions. He also speculated that the development of testosterone’s “competitive-victimizing” effects is the result of natural selection, as described by Darwin.

Scholars who study the relationship between testosterone levels and crime cite as support the differences between males and females in terms of levels of crime in general and levels of violence in particular. This work has led to the “treatment” of male sex offenders with chemical derivatives from progesterone to reduce male sexual urges through the introduction of female hormones (e.g., Depo-Provera, a brand of birth control for women).This has been effective in reducing some types of sex offenses (e.g., pedophilia, exhibitionism), but it has had little or no impact on other crimes or violence.

2. Premenstrual Syndrome and Premenstrual Dysphoric Disorder

Researchers also have investigated the impact of female hormones on behavior in women, beginning with two English cases in 1980 in which two women used premenstrual syndrome (PMS) as a mitigating factor in violent offenses. These efforts led to female defendants in the United States being able to argue reduced culpability due to PMS.

More recently, a more severe form of PMS has been identified. Premenstrual dysphoric disorder (PMDD) is a severe and debilitating form of PMS, distinguished by the level of interference the menstrual process has on the ability of the woman to engage in the functions of everyday life. Interestingly, researchers have established a genetic link to the development of PMDD. Women with a certain genetic structure have increased (abnormal) sensitivity to their own normal hormones, resulting in increased symptoms of emotional and physical stress.

Another phenomenon associated with female hormones is postpartum depression syndrome. Although most new mothers experience symptoms of depression in the weeks or months following birth, which is primarily thought to be due to a decrease in progesterone, approximately 1% to 2% of these mothers exhibit severe symptoms, such as hallucinations, suicidal or homicidal thoughts, mental confusion, and panic attacks. As with PMS and PMDD, postpartum depression syndrome has successfully been used as a mitigating factor in the legal defense of women accused of crimes while suffering from its effects. Both PMS and PMDD, however, are controversial concepts, difficult to diagnose as medical conditions, and argued by some to be social constructions and psychiatric problems instead of medical conditions.

3. Neurotransmitters

In addition to the possibility that human hormones may directly impact behavior, they also may directly impact chemicals that regulate brain activity. Neurotransmitters are chemicals that transmit messages between brain cells, called neurons, and have a direct impact on the many functions of the brain, including those that affect emotions, learning, mood, and behavior. Although researchers have extensively studied more than 50 of these chemicals, research on the biological bases of crime has focused on three of these: (1) norepinephrine, which is associated with the body’s fight-or-flight response; (2) dopamine, which plays a role in thinking and learning, motivation, sleep, attention, and feelings of pleasure and reward; and (3) serotonin, which impacts many functions, such as sleep, sex drive, anger, aggression, appetite, and metabolism.

High levels of norepinephrine, low levels of dopamine, and low levels of serotonin have been associated with aggression. Results from research that has examined the impact of these neurotransmitters are mixed. With all of these chemicals, fluctuations in their levels may result in certain behaviors, and certain behaviors may contribute to fluctuations in their levels (in a reciprocal interaction effect).

Although there is little doubt that there is a direct relationship between levels of various neurotransmitters and behavior, this relationship is extremely complex and nearly impossible to disaggregate. Chemical changes are part of the body’s response to environmental conditions (e.g., threats) and to internal processes (e.g., fear, anxiety), and environmental conditions and internal processes produce chemical changes in the body. This creates a chicken-and-egg question about whether our responses and reactions are the result of changes in our chemistry or changes in our chemistry are the result of our responses and reactions.

4. Diet, Food Allergies, Sensitivities, Vitamins, and Minerals

What one eats impacts one’s body chemistry. High-protein foods, such as fish, eggs, meat, and many dairy products, contain high levels of the amino acid tryptophan. Tryptophan produces serotonin (see preceding section). Another amino acid, tyrosine (also found in high-protein foods), is related to the production of both dopamine and norepinephrine. These relationships have suggested that many aggressive behaviors may be controlled with a diet higher in protein and lower in refined carbohydrates.

Carbohydrates—specifically, refined carbohydrates, such as white refined flour, white rice, white refined sugar, and any processed foods with high levels of sugar—also are examined as related to problem behavior. Complex carbohydrates are slowly transformed into glucose, which stimulates the production of insulin in the pancreas, which in turn produces energy for the body. Simple or refined carbohydrates are not processed slowly and result in the rapid release of insulin into the bloodstream, causing a sharp decrease in blood sugar, depriving the brain of the glucose necessary for proper functioning. This sharp decline in blood sugar also triggers the release of hormones such as adrenalin and increases in dopamine. This combination has been associated with increased aggression, irritability, and anxiety.

The state of having chronically reduced blood sugar caused by the excessive production of insulin is called hypoglycemia. Individuals who are hypoglycemic experience increased levels of irritability, aggression, and difficulty in controlling their emotional expressions. Hypoglycemia has successfully been used to mitigate criminal behavior. The most infamous example occurred during the late 1970s when Dan White killed San Francisco Mayor George Moscone and City Supervisor Harvey Milk after consuming nothing but junk food such as Twinkies and soda for several days. At trial, White’s attorney successfully argued that White suffered from “diminished capacity” due to his hypoglycemia. His argument has come to be known as the “Twinkie Defense” (Lilly, Cullen, & Ball, 2007).

Experimentation with the diets of criminal populations have indicated that reducing intake of refined carbohydrates and increasing consumption of fruits and vegetables have significantly decreased behavioral problems and disciplinary write-ups. It is difficult, however, to separate the impact of diet from other potential factors that may affect behavior.

Other potential contributors related to food intake involve food allergies and the consumption (or not) of various vitamins and minerals. Once again, refined carbohydrates may be a culprit. These types of foods contain particularly high levels of cadmium and lead, two minerals known to cause damage to brain tissue and impact the production of neurotransmitters.

Several food components have been associated with reactions that may include aggressive, violent, or criminal behavior. Some people may be allergic to or exhibit increased sensitivity to chemicals contained in chocolate (phenylethylamine), aged cheeses and wine (tyramine), artificial sweeteners (aspartame), and caffeine (xanthines). Others may react to food additives, such as monosodium glutamate and food dyes. Criminal populations also have been found to lack vitamins B3 and B6 in comparison to noncriminal populations.

5. Environmental Toxins

The frontal lobe of the brain, an area that has become the focus of biological investigations into criminal behavior, is particularly sensitive to environmental toxins, such as lead and manganese. Behavioral difficulties, such as hyperactivity, impulsivity, aggression, and lack of self-control, have been associated with increased levels of these heavy metals.

Examination of the impact of environmental toxins on human behavior is very promising because it integrates biological with sociological and criminological theories. Facilities that produce, store, treat, and dispose of hazardous wastes are largely to blame for the production of environmental toxins. Research has shown that proximity to these types of facilities increases the impairment of the brain and of the general central nervous system, producing lower IQs; reductions in learning abilities, frustration tolerance, and self-control; and increases in impulsivity, hyperactivity, antisocial behaviors, violence, and crime.

Researchers who study the relationship of environmental toxins to crime argue that our environment is producing crime by producing neurological damage. Scholars emphasize the fact that minority populations and lower-income groups are the ones most likely to live near these facilities and as a result are more likely than white and higher-income groups to be negatively impacted by these toxins. This, according to the researchers, may help explain why minorities and people from the lower classes seem to catch the attention of the criminal justice system in higher rates than others.