Hormones, the Brain, and Criminality Research Paper

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“Is biology really relevant to criminology? After all, criminal behavior is learned, right? People aren’t just born criminals; that’s ridiculous.” Critics of the biosocial perspective still use this sort of reasoning to raise doubts about the role of biology in crime causation. However, such thinking overlooks evidence that many personality traits and even human interests and preferences are genetically influenced to a substantial degree (Bouchard and McGue 2003; Kreek et al. 2005; Schermer and Vernon 2008). There is also considerable evidence that all human learning boils down to neurochemical processes that vary from one individual to another (Lawson 2003). Consequently, even though criminality is learned, biology still affects how we learn. To set the stage for examining this line of reasoning further, this research paper will describe the role of a class of biochemicals called hormones in learning criminal behavior. But before doing so, a little background on biosocial criminology is in order.

Criminology’s Biosocial Perspective

The first scientist to make the case for biological influences on criminality was an Italian physician named Cesare Lombroso. Writing in the mid- 1800s, he is most famous for having argued that persistent criminals were atavistic, meaning that they were “throwbacks” to an earlier stage in human evolution.

Today, criminologists’ opinions about the relevance of biology to understanding criminal behavior have gone far beyond Lombroso’s concept of atavism. These opinions can be organized into three rather extreme categories:

  1. Criminal behavior is almost completely determined by biological forces.
  2. Biology and the social environment interact to influence criminal behavior.
  3. Criminality is determined almost entirely by social factors.

According to surveys conducted in recent years, no criminologists subscribe to the first statement, although critics of the biosocial perspective often imply otherwise. About 20 % of criminologists subscribe to the second option, i.e., biological and social factors interact to affect criminal behavior. The remaining 80 % of criminologists still believing that biology has little or nothing to do with people’s involvement in crime (the third option). So, the biosocial perspective remains a minority position among criminologists, although it does seem to have gained a little in popularity in recent decades (Cooper et al. 2010).

As other entries in this biosocial section illustrate, a great deal of progress has been made in recent decades deciphering biological influences not only on criminality but also on several related behaviors (e.g., aggression, risk taking, and susceptibility to alcohol and drug addiction). What has emerged from this research is not the conclusion that people are “hard wired” to be murderers, thieves, robbers, or rapists. Instead, the following four interrelated principles have become part of how biosocial theorists reason:

  1. All human actions are controlled by the functioning of the brain.
  2. Genes and other biological factors profoundly affect how the brain functions in response to whatever environment it encounters.
  3. By affecting brain responses to the environment, biological factors can alter the probability of individuals running afoul of the law.
  4. Hormones are among the most important biological factors influencing brain functioning.

About Hormones

Hormones are substances produced primarily in one part of the body (such as various glands) that travel to other parts of the body (usually by way of the blood system) where they have their greatest effects. The brain is one of the main targets of hormones.

This research paper focuses on two types of hormones. One type is called sex hormones because they exist in greater quantities in one sex than in the other. The other is known as stress hormones because they tend to be produced in greater quantities when individuals are experiencing stress and anxiety.

Androgens: The Hormones From Hell

Those familiar with farm animals – be they cattle, horses, hogs, sheep, or even chickens – know that males are nearly always more belligerent and combative than their female counterparts. What “barnyard culture” is responsible for such a sex difference? Of course, culture is not the culprit; biology is. Even though this is a rather obvious conclusion, think about how quickly people attribute male-female differences in belligerency and combativeness to cultural learning in humans while still recognizing that culture is not responsible for the same sex difference in other animals.

Scientists and farmers alike have learned that sex differences in belligerency and combativeness have hormonal underpinnings partly because they have identified how to eliminate the sex differences using a procedure called castration. This simple operation involves removing the testicles, glandular organs that specialize in producing hormones known as androgens (which collectively refers to all sex hormones that males produce in higher quantities than do females). Within a few months after being castrated, males nearly always become much more passive, like their female counterparts.

Studies have shown that the most influential androgen regarding physically aggression is testosterone. While most androgens are produced by the male testicles, smaller amounts are also synthesized by the adrenal glands (that both sexes have) as well as by the female ovaries. Therefore, even though androgens are called “male sex hormones,” one should keep in mind that females also produce them, only in lower quantities.

Linking Androgens to Criminality. If testosterone and other androgens are responsible for average sex differences in belligerency and combativeness, could these hormones also contribute to criminality? Nearly all biosocial criminologists believe the answer is yes. After all, many crimes have distinctive aggressive elements, especially those crimes committed primarily by males.

Before going further, it is important to note that no one seriously argues that because androgens contribute to criminality, the “solution” to the crime problem is castration! Even so, the fact that castration can dramatically reduce aggression in farm animals provides additional evidence that androgens deserve research attention by criminologists.

One way to think about the potential influence of androgens on criminality involves tracking crime rates over the course of a human lifetime. In this regard, not only are males much more criminal than females, but most male offenses occur between the ages of 13 and 30. The relationships between sex, age, and criminality are illustrated in Fig. 1. This particular graph is based on persons convicted of serious offenses in England and Wales during 2000, but almost exactly the same pattern can be found anywhere else in the world (Ellis et al. 2009, pp. 17–20).

Hormones, the Brain, and Criminality Research Paper

Keep in mind this sex-age-crime relationship shown in Fig. 1 and then look at Fig. 2. This second graph represents the average levels of testosterone in the human body throughout life (adjusted for body weight). This second graph traces testosterone all the way back to conception (for reasons to be explained shortly), but for now simply notice how the rise in testosterone closely parallels a rise in the probabilities of criminal convictions for males as well as for females. These two graphs along with research on how androgens affect the brain provide support for the argument that androgens contribute to criminality. Some of this research will be briefly reviewed.

Hormones, the Brain, and Criminality Research Paper

How Androgens Work. As already noted, androgens appear to affect behavior by altering the brain. But one should add that these alterations primarily occur in two developmental stages, not just one. The first, called the perinatal (or organizational) stage, takes place before and shortly following birth. Refer back to Fig. 2, and notice how males are producing considerably more testosterone than females throughout gestation and for a month or two after birth.

It is during this perinatal stage that the brain becomes irreversibly sexed, i.e., made to be either masculine or feminine, although to widely varying degrees. In the simplest of terms, if androgens are present in low amounts, the brain will be left in its “neutral” or “default” form, which in mammals is feminine. On the other hand, if androgens are present in high amounts, the brain (along with the rest of the body) will be masculinized. (As an aside, the fact that the “default sex” is female explains why males have nonfunctional nipples, testes that are really modified ovaries, and penises that are essentially enlarged clitorises.)

The second stage of brain sexing begins at puberty and continues throughout adulthood as shown in Fig. 2. Basically, to the extent that the male brain is exposed to androgens following the onset of puberty, it begins to function in a fully masculine mode. This second state is referred to as the postpubertal (or activational) stage (Sisk and Zehr 2005). However, it is important to realize that the potential for fully masculine behavior was laid down during the first stage; the second stage merely “turns on” the behavior.

Because female brains receive lower exposure to androgens than do the brains of males, their behavior tends to be much less “androgen influenced.” Nevertheless, there is no simple straightforward relationship between high testosterone at a given point in time and the probability of someone robbing a bank or assaulting a neighbor. This fact has been demonstrated by studies that have correlated postpubertal testosterone levels in the blood or saliva with involvement in crime. The relationships tend to be quite modest (Ellis et al. 2009, pp. 208–210). However, one should keep in mind that neither the blood nor saliva provides a very good indication of how much testosterone is in the brain. Overall, the cause-and-effect relationship between androgens and criminality is complex even though it is still quite real.

Some Detailed Behavioral Effects Of Androgens

Let us consider the behavioral consequences of high androgen exposure in greater detail because it is not just aggression that is affected. In other words, what types of behavior besides those that are illegal and violent are promoted by exposing the brain to androgens?

Competitive-Victimizing (CV) Behavior. Numerous animal experiments have carefully manipulated both perinatal and postpubertal influences of androgens on behavior. These experiments have shown that animals with high exposure exhibit more aggressive and combative tendencies, especially when their access to resources or mates is challenged or blocked (Archer 1994). Regarding the timing of the androgen exposure, it appears that perinatal exposure is actually more important than postpubertal exposure (Romeo et al. 2003).

Studies suggest that the effects of exposing the brain to androgens are similar to the effects in other mammals. Collectively, the behavioral effects of androgen exposure can be described as competitive-victimizing (CV) behavior (Ellis et al. 2008). CV behavior primarily consists of elevated aggression and competitiveness, even in the face of considerable personal risk (Booth et al. 2006; McDermott et al. 2007). In humans, one manifestation of CV behavior is criminality, especially regarding violent and property offenses. The fact that males have higher levels of androgens than females offers a scientific explanation for why males are much more criminal than females throughout the world (Ellis et al. 2009; McDermott et al. 2007; van Bokhoven et al. 2006).

The idea that brain exposure to androgens is a major cause of sex differences in criminality and for the dramatic rise in male offending in the teenage years is visible when one compares Figs. 1 and 2. However, there is one interesting discrepancy revealed when comparing these two graphs. Notice that after age 30 or so, male offending rates drop off dramatically (Fig. 1) even though testosterone levels remain quite high (Fig. 2). How can this inconsistency be explained?

One proposal has been that the discrepancy reflects the influence that learning has on criminality (Ellis 2005). In particular, to the extent that males learn how to compete for resources and mates in ways that minimize the risk of retaliation by victims, their offending rates will rapidly decline. Thus, males with difficulty learning will have longer criminal “careers” than males who learn quickly.

Imagine two hypothetical males whose brains have been equally androgenized. Assume that one of these boys is able to learn quickly and the other one requires much more time. Theoretically, they should both be involved in some degree of delinquency during adolescents. However, the quick-learning boy should transition within a year or so into a socially responsible citizen who is able to compete for resources without violating the law. The slow learner, on the other hand, may take decades to finally “settle down.”

One criminologist made the essential distinction between two types of offenders. She termed one “adolescent limited” and the other “life-course persistent” (Moffitt 1993). Both types engage in delinquency during their teenage years, but only the latter continues to offend as full adults. This distinction can be merged with the idea that androgens contribute to criminal activity by noting that both types of offenders will still be predominantly males. The males who become life-course-persistent offenders will be mainly those who have the greatest difficulties learning (nearly always due to some underlying neuropathology). This line of reasoning is supported by numerous studies documenting lower IQ scores, more learning disabilities, and higher school dropout rates among the most serious and persistent offenders (Ellis et al. 2009, pp. 150–159).

Did Criminal Behavior Evolve?

Another aspect of biosocial criminology has involved exploring the possibility that criminality has evolutionary roots. This means that the commission of crime could be part of how many individuals, particularly males, pass their genes on to subsequent generations (Ellis 2008; Rowe 1996).

At the heart of the argument is that over countless generations, females who have chosen mates who are unusually ambitious and competitive have left more of their (and their mate’s) offspring in subsequent generations than is true for females who use other criteria when choosing mates. As a result, males may have evolved tendencies to victimize others, including in ways that most people deem criminal.

Hormones And Stress

Not all hormones are involved in sexual differentiation. Some hormones are released into the blood system primarily during times of stress. These are known as stress hormones. One stress hormone, called cortisol, has been repeatedly found associated with persistent criminal behavior (Ellis et al. 2009, pp. 210–213). However, unlike androgens that tend to be positively correlated with offending rates, cortisol levels are inversely correlated. In other words, criminals usually exhibit lower levels of cortisol levels than do persons in general.

How might the relationship between low cortisol and criminality be explained? Most proposals have reasoned as follows: Having elevated levels of cortisol tends to be relatively unpleasant. Individuals with high cortisol levels, or with cortisol levels that rise rapidly whenever they begin to experience stress, will be more easily deterred from engaging in whatever behavior is associated with elevated cortisol.

Consistent with such reasoning, low levels of cortisol have been found associated not only with criminality but also with childhood conduct disorders, persistent childhood aggression, and attention deficit hyperactivity disorders (Pajer et al. 2001). It is not very surprising to learn that all of these childhood traits have been found to be statistically associated with involvement in criminal behavior later in life (Ellis et al. 2009, p. 213).

Overall, persons who are most likely to exhibit these behavior patterns have lower “resting” levels of cortisol, or, when they experience stressful events, their cortisol levels rise very little (Gordis et al. 2006). Consequently, individuals who happen to be “hyporesponsive” to stress in terms of cortisol levels are more likely to be involved in crime.

Why do people vary in cortisol levels, especially in response to stress? Studies based on twins have revealed that genetic factors are important (Bartels et al. 2003; Wust et al. 2000). There is also evidence that cortisol may actually interact with testosterone to affect offending behavior (Terburg et al. 2009). Ultimately, no matter what causes low cortisol levels and high androgen levels to be associated with criminality, their relationships provide further evidence that criminology without biology is incomplete. Biosocial criminologists are in a unique position to help bring these two important disciplines closer together.


Unlike the majority of criminologists who still argue that only learning and social variables are needed to explain criminal behavior, biosocial criminologists incorporate biological factors into their theories and research. This research paper has provided a thumbnail sketch of how two types of hormones appear to be relevant to understanding criminal behavior – sex hormones and stress hormones.

Regarding sex hormones, androgens appear to be central to the sexual differentiation of both the brain and the rest of the body. By affecting the brain, androgens increase the chances of many forms of competitive/victimizing behavior. Several extreme types of such behavior have been criminalized in all societies. Because male brains are exposed to higher levels of androgens, their contribution to crime is considerably greater than that of females.

At least one type of stress hormone – cortisol – has also been found associated with involvement in criminal behavior. Unlike androgens, it is unusually low levels of cortisol that are linked with criminality.

Despite the simplicity of the idea that both sex hormones and stress hormones are associated with criminality, one should appreciate that there are complex chains of events that still need to be considered as one attempts to understand the connections. For instance, most effects of hormones on behavior appear to be mediated by neurotransmitters (chemicals in the brain that help transmit signals from one nerve cell to another) (Birger et al. 2003).

Will biosocial criminology ultimately help reduce the crime problem? In all likelihood, yes (Archer 1994; Ellis 2008; MacGillivray 1997). Some critics of biosocial criminology fear that this perspective could reopen the door to Nazistyle “solutions” to crime and other social problems (Mitchell and Richard 1998). However, the risks are low in democratic societies where people insist on balancing concerns about public safety with respect for individual freedom and liberty. Also, most people understand that human behavior is much too complex to ever be easily manipulated exclusively at biological levels.


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