The Anatomy of Violence

by Adrian Raine

  Minor physical anomalies assessed by pediatricians at age twelve predicted violent offending at age twenty-one by perpetrators now leaving school and graduating on to violent criminal careers.46 Yet again, a biosocial interaction was observed with especially high rates of violence found in those with both minor physical anomalies and a history of being raised in unstable home environments. As with birth complications, the presence of a negative psychosocial factor is required to trigger the biological risk factor in adults—and in both cases the effects are specific to violent offending.

  It may seem bizarre. Some of Lombroso’s ideas may seem very repugnant. Yet over a hundred years after his first theorizing, we can say that Lombroso was at least partially on the mark with his theory for Cain-like atavistic stigmata for criminal offending. We can also say—at least at a superficial level—that the book of Genesis highlights for us external physical indicators of family feuds gone wrong. The key difference is that while the mark on Cain in Genesis was very visible, we never notice anyone’s minor physical anomalies. They are imperceptible without a close physical examination.

  From a scientific standpoint we get another pointer to the fact that the seeds of violence are sown very early on in life—as early as the prenatal period.

  FROM PALM PRINTS TO FINGERS

  How often do you look at your fingers? In all likelihood, not very often. But take a look right now at your right hand.47 With your palm facing you, look at the length of your fingers. Compare the length of the second digit with the length of the fourth digit. The second digit is your index finger, the fourth digit is your ring finger. You’ll very likely see that the fourth digit is longer than the second. It is for most people, especially on the right hand. If you can compare yourself with someone of the opposite sex, see who has a longer ring finger relative to the index finger. Males in general have the advantage—they tend to have a longer ring finger compared with their index finger than women do. This gender difference is also true in baboons.

  What causes this difference between the genders? Genetics is one explanation, with the same set of genes48 influencing both genitals and digit length.49 But in addition, fetal hormone exposure—in particular androgens—plays a critical role. Sometime between ten and eighteen weeks of gestation there is a major surge in testosterone production that among other things produces the primary gender differences we see at birth. It not only masculinizes the nervous system and behavior, but it also influences the ratio of the length of the second to the fourth digit.50 The higher the testosterone exposure, the longer the size of the ring finger relative to the index finger. Hence men have a relatively longer ring finger than women.51

  The testosterone explanation of the digit difference seems relatively convincing. Several studies have observed that children with congenital adrenal hyperplasia52—a condition caused by high prenatal androgen exposure—shows this male effect of a relatively longer ring finger.53 Women who have larger waists relative to their hips often have higher testosterone levels, and such women have been found in turn to give birth to children with relatively longer ring fingers.54 Indeed, because assessing prenatal androgen levels is not easy, this finger difference has been touted as an indirect indicator of the level of androgens during fetal development.55

  What do we know about people with a more male-like, longer ring finger? For one thing they tend to dominate, show physical advantages, have male-like characteristics, and have personalities linked to aggression. A study in Poland shows that females who have achieved elite status in athletics have relatively longer ring fingers compared with non-elite athletes.56 And such prowess is not restricted to the track or to Poland. Male British symphony orchestra musicians also have relatively longer ring fingers.57 On the field, English soccer players who are in the first team have longer ring fingers than those who are in the reserves.58 Some of you may recall the likes of Paul Gascoigne, Geoff Hurst, Stanley Matthews, Peter Shilton, Glenn Hoddle, Kenny Dalglish, and Ozzie Ardiles—soccer stars who represented their countries in international matches. These twenty-nine stars, as a group, were found to have longer ring fingers than a group of 275 professional footballers who had not played for their country. Furthermore, the more times they had represented their country, the longer their relative ring-finger length.

  Another correlate of the long ring finger is sensation-seeking and impulsivity59—personality traits that we saw in the previous chapter to be linked to antisocial and violent behavior. People who are relatively lacking in empathy also have longer index fingers,60 and antisocial, psychopathic offenders certainly lack empathy. Although the evidence is conflicting, men with a longer ring finger tend to have higher attractiveness ratings.61 Hyperactive children have a longer ring finger,62 and we know that there is comorbidity between hyperactivity and conduct disorder. Gay men’s ring-finger lengths are often in between those of heterosexual men and heterosexual women.63 It’s not true of every study, but in a sense relatively longer ring fingers compared with index fingers go along with male characteristics—high stimulation-seeking, low empathy, and hyperactivity.

  Given this, it perhaps comes as no surprise that higher aggression—a very male characteristic—is associated with longer ring fingers. In Canada, male undergraduates who are more physically aggressive have longer ring fingers,64 with the strength of this relationship being as strong as the relationship between aggression and testosterone. In the United States, male undergraduates with longer ring fingers report being both more aggressive and more likely to engage in male-related play activities.65 In China we have been finding cross-cultural support for the relationship between high aggression and a longer ring finger in male but not female eleven-year-old schoolchildren.66

  We often think of aggression in the domestic domain as a bit different from aggression toward strangers. Indeed, the field of domestic violence has been almost completely dominated by scientists with a strong social perspective on intimate partner violence. But relative ring finger length, with its status as a marker for prenatal testosterone levels, sticks up a rude finger gesture to this predominantly social view. Men with long ring fingers are more likely to use threats of aggression against their female romantic partners.67 They are also more physically violent toward them, and this is especially true for men whose female partners are cheating on them.68

  By and large, the relative ring finger length relationship with physical aggression seems to be more true for men than for women. So what’s going on beneath the Tarzan/Jane stereotypes of aggressive men and nurturing women? I think part of the answer is that women are just less aggressive than men, so aggression scores are more likely to bottom out in women. There is less variability in aggression to explain here. That is something we call a floor effect, and it can suppress relationships. But more likely it’s because, as we saw in chapter 1, hard-core physical aggression is costly in an evolutionary sense. Women invest in their offspring more than men, and a woman who initiates violence is likely to be hit in return, which could be a danger to the survival of her offspring—more than would be true for the father of the child. So instead, more “softer” forms of aggression—like gossiping, rumormongering, making others feel guilty, and shutting others out of relationships—are more in the female domain than full-blooded physical aggression. Once we get down to assessing these softer forms of “relational” aggression in women, studies do indeed find relationships between such behaviors in females and longer ring-finger lengths.69 They also show a relationship between finger ratios and more “reactive aggression”—lashing out at others who have hurt or slighted them.70

  And what about aggression in the political arena? If you were the leader of a country and in conflict with your neighbor over diamond mines that had just been discovered in disputed territory, how would you react? Suppose you can either negotiate or go to war. Your choice is not entirely as free as you may think. It’s partly determined by your relative ring-finger length. Business-school students at Harvard were placed in this game
scenario.71 The interesting parameter was the number of unprovoked attacks the leader would make on the neighboring country. As you might expect, men in general launched more unprovoked attacks than women—32 percent versus 14 percent. Let’s remember that by the tender age of one year, boys are already throwing and hitting more than girls.72 But what’s more interesting is that the students with longer ring fingers launched more unprovoked attacks, an effect that was as strong as the gender difference in aggression.73 If you are a Quaker, check out your political candidates’ finger lengths before casting your vote.

  Why should this mark of Cain—the longer ring finger than index finger—be a characteristic of aggressive individuals? Of course, the longer ring finger itself is not causing crime. It’s more that other factors that go into making a longer ring finger also go into making aggression. We have just seen how higher testosterone in utero is responsible for the digit difference. In chapter 4 we also saw how high testosterone is causally related to aggression. So perhaps we have it here—the longer ring finger is caused by high prenatal testosterone, which in turn fuels aggression. That higher surge in testosterone early in fetal development shapes a more prototypical male brain, which shapes more prototypical male behaviors, including sensation-seeking, interest in sports, low empathy, dominance, and, of course, aggression.

  But is there something missing here, a question that begs to be answered? What causes higher testosterone exposure in utero? Smoking cigarettes during pregnancy can result in higher prenatal-testosterone exposure to the fetus that leaves its mark on finger length. We suspect this because mothers who smoke have higher testosterone levels, and this can in turn reduce estrogen exposure to the fetus, resulting in higher fetal testosterone levels. Experimental work in animals has shown a causal connection, with exposure to nicotine in the prenatal period resulting in higher testosterone in the fetuses.74 Given these links, it’s not too surprising that mothers who smoke during pregnancy have male offspring with longer ring fingers than mothers who do not smoke.75

  There is something elegant in this line of research. Unlike brain-imaging research, where we can observe structural and functional changes to the brain that may be caused by violence and subsequent head injury, the digit difference precedes even the very initial development of antisocial, aggressive, and violent behavior. How do we know that for sure? Ultrasound can give us images of fetuses, but it’s not possible to assess finger-length differences from such images. However, researchers in Turkey examined 161 fetuses that had been aborted at different stages of pregnancy and made exact measurements of finger lengths. They established that the gender difference was present by the end of the third month of gestation.76 There really does seem to be a process in place very early on in life that contributes to aggression many years later.

  Relative finger length, then, provides us a window backward in time to view what occurred during fetal development. It suggests not only that Lombroso was partly correct, but also that the pre-birth period is more important than we have previously thought. Of course, mothers cannot control their hormone levels during pregnancy—they are not in any way to blame if their child is exposed to higher testosterone and becomes aggressive later in life. But there are other things she knowingly does that will shape the fate of her child in a negative direction.

  SMOKING DURING PREGNANCY

  Smoking is not good for your health. But it can do wonders for your violence potential, especially if your mother smoked like a chimney while she was pregnant with you. We now know that if a mother smokes during pregnancy it not only has negative consequences on brain development, but it also leads to increased rates of conduct disorder and aggression in her offspring. A spate of studies has established beyond a reasonable doubt a significant link between smoking during pregnancy and both later conduct disorder in children and violent offending in adults. A number of these studies are impressive in terms of their size, the prospective nature of data collection, long-term outcome, and control for third factors, suggesting that the relationship is causal.

  Using the birth cohort from Denmark that included 4,169 males, the psychologist Patty Brennan at Emory University found a twofold increase in adult violent offending in the offspring of mothers who smoked twenty cigarettes a day.77 She also found a dose-response relationship, with an increase in the number of cigarettes smoked resulting in a linear increase in adult violence. It was an impressive study, and there are many others like it in different countries.

  In one birth cohort of 5,966 from Finland, the offspring of mothers who smoked were twice as likely to have a criminal record by age twenty-two.78 In a follow-up study of this Finnish sample to age twenty-six, a twofold increase in violent crime and repeat offending was found in the offspring of mothers who smoked.79 In the United States, boys of mothers who smoked ten cigarettes a day during pregnancy were four times more likely to have conduct disorder.80

  These samples are predominantly Caucasian—are the same effects found for other ethnic groups? They do seem to hold for African-Americans, at least. The same effect of prenatal smoking exposure in increasing both conduct disorder81 and disruptive behavior problems82 has been observed in African-American children. One U.S. study showed more than a fourfold increase in conduct disorder in the offspring of mothers who smoked half a pack of cigarettes a day,83 and another found an increase of six points in behavior problems in three-year-olds exposed to smoking during the third trimester.84 In New Zealand, a doubling in the rate of conduct disorder was found in the offspring of maternal smokers.85 You find the same relationship between prenatal smoking and antisocial behavior in Welsh children and adolescents.86 Wherever you go in the world, you get the same finding.

  Of course, you’ve probably already asked yourself a very good question: Could it be that mothers who smoke during pregnancy are not, on average, the most caring, educated, empathic, and informed parents in the world? Someone willing to subject her unborn child to toxins in the womb may not be providing the best environment after a child is born. To illustrate this point further, in one study a full 72 percent of the offspring of mothers who smoked during pregnancy had experienced either physical or sexual abuse. In addressing this important issue many of the studies have taken pains to control for third factors that could account for the smoking-antisocial relationship. But even then, crime and antisocial personality in the parents, low socioeconomic status, low maternal educational level, mother’s age at the child’s birth, family size, poor child-rearing behaviors, bad parenting, obstetric complications, birth weight, family problems, parental psychiatric diagnoses, attention-deficit/hyperactivity disorder, offspring smoking, and other drug use during pregnancy could not account for the relationship. After that shopping list of confounds, there’s not a lot left to control for. Taken together with the dose-response relationship that was also established in several of the studies, these findings appear to be real, and suggest a causal relationship between smoking during pregnancy and later violence.87

  Every puff counts. Studies repeatedly show that the more cigarettes the mother smokes, the greater the odds of antisocial behavior in her offspring. We’ll also see later in the book that many other factors combine together with maternal prenatal smoking to really boost the odds of violence in their offspring.

  It’s my hope that if you are reading this and you are pregnant you will decide to quit for the good of your little one. But I should warn you that this alone may not be enough. If your husband or co-workers smoke, you are still exposing your baby to the toxic effects of smoking. Lisa Gatzke-Kopp, at Penn State University and a past graduate student of mine, found that secondhand exposure to cigarette smoking predicted conduct disorder even after controlling for antisocial behavior in the parents, poor parenting practices, and other biological and social confounds.88

  How can a few puffs during pregnancy cause the fetus to become a fighter later in life? What is the nature of the causal path from fetal nicotine exposure to antisocial behavior? First and foremost
, it can partly account for the brain deficits that we saw to be apparent in brain scans of adult offenders. Animal research has clearly demonstrated the neurotoxic effects of two constituents of cigarette smoke—carbon monoxide and nicotine.89 Nicotine passes across the placenta, directly exposing the fetus. A primary effect is that it reduces uterine blood flow and consequently reduces both nutrients and oxygen to the fetus, producing hypoxia, which can damage the brain. Babies exposed to smoking have been shown to have a reduction in head circumference, indirectly reflecting a reduction in brain development.90 Studies of brain-scanned adults who were exposed as a fetus to maternal smoking show that they have thinner orbitofrontal and middle frontal gyral thickness—brain areas that we will see in a later chapter are especially implicated in violence.91

  Because smoking negatively affects the fetal brain, we would expect such exposed infants to show neuropsychological impairments later on in childhood and adolescence—and they do. Studies have documented impairments in selective attention, memory, and speed in processing speech stimuli.92 A dose-response relationship between increased cigarette smoking and reductions in arithmetic and spelling between ages six and eleven has been reported.93 We’ve seen that neurocognitive functions are impaired in offenders, and we also know that such offenders fail in school, where math and spelling abilities are important. Fetal exposure to smoking is a likely contribution to this neurocognitive pathway to antisocial and violent behavior.

  Prenatal nicotine exposure, even at relatively low levels, disrupts the development of the noradrenergic neurotransmitter system.94 This is of particular significance in the context of the autonomic deficits we discussed earlier. Reduction of noradrenergic functioning caused by smoking would be expected to disrupt sympathetic nervous system activity. As we saw earlier, reduced sympathetic arousal as measured by sweat rate has been found in antisocial individuals. Furthermore, when pregnant rats are exposed to nicotine at the levels commonly found in human smokers, the offspring show an enhancement of cardiac M2-muscarinic cholinergic receptors. These receptors inhibit autonomic functions,95 so stimulation of their functioning via smoking would reduce autonomic functioning and help explain the well-replicated finding of low resting heart rate in antisocial individuals outlined earlier. It would also help explain the impaired autonomic functions that we have seen in offenders, such as reduced electrodermal fear conditioning. In essence, when the fetus is exposed to smoking, the sympathetic nervous system gets shut down—and the outcome can be an under-aroused, stimulation-seeking individual.