The Anatomy of Violence (45 page)

This is not to say that antisocial children from adverse home backgrounds will never have biological risk factors for antisocial and violent behavior—they clearly will. Instead, the argument is that in such situations the link between antisocial behavior and biology is watered down because the social causes of crime can camouflage the biological contribution. Social causation will be more salient in children from adverse homes. In contrast, when the home is normal, but the child is not, then a bad brain may be the culprit. Here the social spotlight on violence is dimmed—and what now shines through is biology.
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So far I’ve illustrated the social-push hypothesis with respect to poorer
frontal functioning in murderers from benign home backgrounds, and
low fear conditioning in antisocial kids from poor homes. Yet this pattern of results has been found for a whole host of biological risk factors. As a graduate student I observed the social-moderation effect again soon after seeing the conditioning effect, finding that low resting heart rates particularly predispose schoolchildren from
higher
social class homes to antisocial behavior.
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More important, a number of other scientists have seen the same thing. Antisocial children from privileged middle-class backgrounds attending private schools in England have low resting heart rates.
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Antisocial English children from intact but not broken homes have lower heart rates.
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Low resting heart rate also characterized English criminals without a childhood history broken by parental absence and disharmony.
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In the
Netherlands, Dutch
“privileged” offenders—those from high-social-class homes who commit crimes of evasion—show blunted skin-conductance reactivity.
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In
Mauritian children, reduced
skin conductance responding to neutral tones at age three—a measure of “
orienting,” or poor
attention—is related to aggressive behavior at age eleven, but only in those from high-social-class backgrounds.
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Similarly in adults, English prisoners who are emotionally blunted and who come from intact homes—but not broken homes—show reduced skin-conductance orienting.
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Catherine Tuvblad, in Sweden, found that the environment
moderates
the link between genes and environment. As we might expect from what we learned about genetics in
chapter 2
, she found a genetic contribution to antisocial behavior in boys, but only those from a
good
home background.
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This same moderation effect has been observed at a molecular genetic level where
abnormalities in
genes related to the neurotransmitter
dopamine
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are associated with early arrests, but only in adolescents from
low-risk
family environments—those who are socially better off. Again, genetic factors shine forth more in explaining
antisocial behavior when social risk factors are less in evidence.

My student graduate
Yu Gao also documented a moderating effect with the
Iowa gambling task—a neurocognitive indicator of orbitofrontal functioning. Our colleagues
Antoine Bechara and
Antonio Damasio had demonstrated that patients with lesions to the ventromedial
prefrontal cortex did poorly on this task and also showed psychopathic behavior.
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You’ll recall from
chapter 5
that the
orbitofrontal cortex is critical for generating
somatic markers that inform good decision-making and that it also facilitates good
fear conditioning. This task was given to schoolchildren alongside assessments of psychopathic-like behavior.
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Gao found that kids who did poorly on the orbitofrontal gambling task were more likely to be psychopaths—but only when they came from normal home backgrounds.
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Just as I’d previously shown that poor fear conditioning predisposes children from good homes to antisocial behavior, so Gao took a measure of this same orbitofrontal cortex and showed the same moderating result.
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Moving from the lab to the real world, we can see the social-push hypothesis in cases of killers. Randy
Kraft, the Scorecard Killer, had a very supportive and stable home background. Similarly,
Jeffrey Landrigan had the best of home environments, yet went on to become a death-row inmate.
Kip Kinkel, a teenager who killed his parents as well as two children at his high school, had a caring home environment in rural Oregon. His parents were devoted professionals, and he had a loving sister. We’ll see later the orbitofrontal dysfunction that contributed to his
violence. You cannot pin the blame on
poverty, bad
neighborhoods, or
child abuse all the time—certainly not in these cases. Nor is social deprivation so obvious in many more murderers who, while not exactly having heavenly homes as kids, did have homes not much different from yours and mine.

Social factors interact with biological factors to increase a propensity for violence. They also moderate the relationship between biology and
violence. There’s a third way to view the influence of the environment on biology, but before we peek into that window on the violent soul we need to step back briefly to
genes, the
brain, and behavior.

Figure 8.5
   Genes give rise to brain abnormalities that in turn predispose to violence

We’ve already discussed brain mechanisms and the violent mind. We’ve seen how specific genes link to violence. Now we’ll survey the building site where genes provide the scaffolding to structural and
functional brain abnormalities supporting the foundations of violent behavior.

You can view my blueprint in
Figure 8.5
. We start at the top left with genes. They link to both brain structure
and
influence neurotransmitter functioning (such as
MAOA). Below that we have brain structure.
The two bottom-up structures thought to support violence are down below in the
limbic system and up top in the
frontal cortex. Within each of these two broad
brain regions, specific structures are identified—including the
amygdala and
orbitofrontal cortex—that contribute to the emotional and
cognitive characteristics of offenders. We then have adult violence and two important variants that predispose someone to it—
antisocial personality disorder and psychopathy. Each of these two variants has different behavioral and emotional elements. Limbic structures give rise to the more affective, emotional components of violence, while frontal impairments result in the cognitive and behavioral dysfunction seen in offenders.
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How exactly do these genes produce aberrant brain conditions that predispose someone to violence? Recall the low
MAOA–antisocial link. Males with this genetic makeup have an 8 percent
reduction in the
volume of the amygdala, the
anterior cingulate, and the orbitofrontal cortex.
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We know that these brain structures are involved in emotion and are compromised in criminals. From genes to brain to offending.

Let’s take the BDNF gene as another example. BDNF—brain-derived neurotrophic factor—is a protein that promotes the survival and structure of
neurons and influences dendrite growth.
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Because mutant
mice bred to have reduced BDNF have a thinner cortex due to neuronal shrinkage, we know that BDNF maintains neural size and dendritic structure.
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BDNF promotes the growth and size of the
hippocampus, which regulates aggression.
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BDNF also promotes cognitive
functions,
⁶⁵
as well as
fear conditioning and
anxiety.
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Given that offenders have poor fear conditioning, blunted emotions, and reduced volume of prefrontal gray matter, there is no surprise that the genotype conferring
low
BDNF is associated with increased impulsive aggression in humans.
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Mice made deficient in BDNF become highly
aggressive and prone to risk-taking, just like their human counterparts.
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Again, we go from genes to brain to aggressive behavior. While this particular subfield of neurocriminology has a very long way to go, we are starting to connect the dots—beginning with malignant genes, moving into brain impairment, and culminating in crime. Nevertheless, it’s going to be more complicated. I’m going to argue that the social environment, far from taking a backseat in this genetic and biological voyage to violence, is driving this Wild West stagecoach.

You now know that the social environment is a causal agent in the brain changes that shape violence. After all,
head injury is caused by what happens to you in your social world. You fall down and your head takes a hit. You have a car crash resulting in a whiplash injury. You were
shaken as a baby. Whether it is what people deliberately do to you, or life’s luckless accidents, your brain gets damaged. And it is that damage that can unleash the devil within you—the unbridled, disinhibited influences that we saw in
Henry Lee Lucas,
Phineas Gage, and many others.

But the environment is even more powerful in influencing the brain than you might imagine. Let me take you back to your childhood, but perhaps change things around a little. Suppose that now you are living in a neighborhood where violence is more commonplace than normal. You’re an eleven-year-old girl or boy, and coming up soon you are going to have a standardized
school test on vocabulary and reading. Then, out of the blue, someone living in your immediate neighborhood is shot dead. Compared with other kids in your class who have the same smarts as you but who did not have a dead body dumped on their doorstep, you do more poorly on the test.

This is what
Patrick Sharkey, a sociologist at New York University and past student of the leading criminologist
Robert Sampson, observed in an innovative data analysis of more than a thousand children in the
Chicago Project on Human Development.
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If a homicide took place in the child’s block four days before testing, it reduced reading scores by almost ten points—or two-thirds of a standard deviation. Similarly, it reduced vocabulary scores by half a standard deviation.
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How big are these effects? Placing them into context, the relationship between homicide exposure and reading scores is as strong as the relationship between distance above sea level and average daily temperature. It’s as strong as the effectiveness of a mammogram in detecting breast cancer.
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Similarly, the relationship found between homicide exposure and vocabulary scores matches the relationship between IQ scores and job performance.
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Put still another way, Sharkey estimated that about 15 percent of
African-American children spend at least one month a year doing poorly at school purely due to homicides in their
neighborhoods.
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These effects are really not trivial.

We see here that it’s not just
direct
social experiences like physical child abuse that can change a child’s cognitive functioning. Even in the dark shadow of social experience, something indirect in society can affect your brain. An insidious effect of social experience can profoundly change neurocognitive functioning.

What precisely is going on here in the
neighborhoods of Chicago and other cities with a twinning of high homicide rates and poor school performance? Sharkey did not have any neurobiological data on the children he studied, but if he did I would expect to see subtle but meaningful changes in brain functioning in children exposed to neighborhood homicide. We know that excessive release of
cortisol in response to stress is neurotoxic to pyramidal cells in the hippocampus—a brain region critical for learning and memory.
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It kills them off. It seems reasonable to hypothesize that children who hear about a homicide around the corner get scared out of their wits. Is this going to happen to their family? Can they walk to the store safely? Are they going to be next? That fear and stress can translate into temporarily impairing brain functioning and cognitive performance.

If this mechanism is meaningful, you might expect a temporal relationship between the occurrence of the homicide and the reduction in cognitive performance. Suppose you are a child who has heard that someone was killed a few blocks away from you. Would you be more stressed at school if you received that news just a few days ago—or several weeks ago? Likely you would be most affected in the first few days. That’s exactly what Pat Sharkey found. The cognitive decline was present when the homicide took place four days before the test, but not when it took place four weeks before.

What about the proximity of the homicide and your level of fear? If it took place in the block you lived in—as opposed to a more distant area of your neighborhood—wouldn’t that be a lot scarier? Might it not create a greater cognitive decline? It did. For both reading and vocabulary, homicides in the nearby block had a stronger effect on the child’s performance than homicides taking place further away in the neighborhood.