Biological explanations of violence are much in vogue. Part of the reason is that scientists studying the seat of behavior, the brain, and its genetic underpinnings, have learned a lot in recent years. Tendencies toward violence, they tell us, may reside in our genes or be hard-wired into our brains. Some neuroscientists have mapped brain abnormalities in laboratory animals and human murderers that seem to correlate with aggressive behavior. Others have teased out apparent connections between violent behavior and brain chemistry.
Being scientists, these researchers often try to tone down and qualify the connection between violence and biology. But even a faint message seems to fall on extraordinarily receptive ears. The findings of a team of Dutch and American scientists, for example, were recently exaggerated not only by the lay media but by the technical press as well. The researchers had come across a Dutch family in which, for five generations, the men had been unusually prone to aggressive outbursts, rape, and arson. These men were also found to have a genetic defect that made them deficient in an enzyme that regulates levels of the neurotransmitter serotonin. Han Brunner, a geneticist at University Hospital in Nijmegen, the Netherlands, and a member of the team, cautioned that the results concerned only one family and could not be generalized to the population at large, but the caveat was ignored. Stories everywhere, in both the scientific journals and the general media, spoke of his finding an aggression gene.
There are other examples. In a 464-page assessment of the state of violence research in 1992, the National Research Council devoted only 14 pages to biological explanations. Of those 14, genetics occupied less than two pages. All the same, the New York Times covered the report with the headline study cites role of biological and genetic factors in violence. Indeed, the proliferation of genetic explanations for violence prompted a Time writer to note wryly: Crime thus joins homosexuality, smoking, divorce, schizophrenia, alcoholism, shyness, political liberalism, intelligence, religiosity, cancer, and blue eyes among the many aspects of human life for which it is claimed that biology is destiny.
Editors, of course, usually know what’s on the minds of their audience: from rapes and murders in Rwanda or Bosnia to wrong-turn drivers cut down in a Los Angeles cul-de-sac, senseless violence has seemingly become the norm. Theater and movie audiences in the 1950s were shocked by The Bad Seed, the tale of a prepubescent pigtailed blond girl who was revealed to be a multiple killer. Today Americans are numb to nightly news reports of assaults in once-protected middle-class neighborhoods, child and spousal abuse in outwardly respectable homes, and clean-cut teenagers or even young children killing each other. The American Academy of Pediatrics made violence the theme of its meetings in October 1996, and the American Medical Association has alerted us to the epidemic of violence.
This morbid fascination is to some extent justified: violence is pervasive. Homicide is the second leading cause of death among teenagers and young adults and the leading cause among African American women and men between the ages of 15 and 34. In the past few decades, the demographics of violence in the United States have taken a turn for the worse. Almost 80 percent of murders used to involve people who knew each other. That figure has fallen to less than 50 percent. These statistics suggest that your chances of being wiped out by someone you’ve never met, and probably for no reason at all, have risen.
The escalation in random violence, especially among adolescents, has generated a hunger for explanations. Biological accounts of murderous behavior do as well as any, and better than most. They are easy to grasp in principle, and they are socially convenient, locating criminal tendencies in our natures, about which we can currently do little beyond incarcerating the wrongdoers, rather than in nurture, which we might be able to remedy if we chose to invest the time and money.
The long, embarrassing history of biological theories of violence suggests caution. In the mid-nineteenth century, phrenologists--who diagnosed personality traits by the location of bumps on the head--worked out a behavioral map of the human skull, determining that area number 6 (out of 35) was the seat of destructiveness. In the early twentieth century some biologists and psychologists sought to extend the newly minted science of genetics to explanations of pernicious behavioral traits. Like today’s scientists, they worked in a context of mounting social problems, including the disruptions of industrial capitalism and the flooding of immigrants into the nation’s cities. They convinced themselves that poverty, alcoholism, prostitution, and criminality leading to violence all arose, in the main, from a trait called feeblemindedness, an inherited condition that they claimed was transmitted from one generation to the next as regularly and surely as the color of hair or eyes. Henry Goddard, the leading authority on the subject in the United States, taught that the feebleminded were a form of undeveloped humanity, a vigorous animal organism of low intellect but strong physique--the wild man of today.
Perhaps not surprisingly, Goddard’s theories were suffused with the bigotry of his era. Feeblemindedness was held to occur with disproportionately high frequency among lower-income and minority groups-- notably recent immigrants from eastern and southern Europe. The biologist Charles Davenport, director of the Carnegie Institution Station for Experimental Evolution in Cold Spring Harbor, New York, and one of the country’s prominent eugenicists, predicted that the great influx of blood from Southeastern Europe would rapidly make the American population darker in pigmentation, smaller in stature, more mercurial . . . more given to crimes of larceny, kidnapping, assault, murder, rape, and sex- immorality.
Such explanations of violence were commonplace in their day, but of course they proved to be hogwash, of no greater merit than the phrenological theories that had preceded them. The scientists responsible for them generally ignored the role of environment in shaping human behavior. They neglected to consider that the genetic contribution to aggression might well be very limited and, to the degree it might exist, very complex, the product of multiple genes acting in concert.
All the same, blaming violence on biology never lost its appeal to the media, the public, and even some scientists. In the mid-1960s a team of British researchers reported that a disproportionate number of male inmates in a Scottish hospital for patients with dangerous, violent, or criminal propensities had an extra Y chromosome accompanying the normal male complement of one X and one Y. Eventually, further research showed the double Y to be irrelevant to violent behavior, but not before lawyers representing the notorious Chicago multiple murderer Richard Speck announced that they planned to appeal his case on the grounds that he was xyy and therefore not responsible for his criminal acts. As it turned out, Speck didn’t have the double Y chromosome after all, but the publicity helped inspire others to take up the banner. Time and Newsweek spotlighted the alleged relationship between chromosomes and crime, and a series of novels such as The xyy Man and The Mosley Receipt by Kenneth Royce featured an xyy character who struggled against his compulsion to cause havoc.
Today’s biological theories of violence are far more sophisticated than their forebears. Unlike the earlier theories, they are concerned with behavior in individuals rather than groups, and they tend to be sensitive to the role of environment. They are also the product of some of the most powerful tools of modern science, including the ability to identify and isolate individual genes and to obtain pictures of the living brain. Unlike the phrenologists, neurobiologists can see--and show us--what may be wrong in a criminal’s head.
Brain scans in particular seem to give a dramatic view into the biological dynamics of violence. Early pet-scan studies in the 1980s revealed that the brains of convicted criminals who had been victims of child abuse had areas of inactivity relative to the brains of control subjects (probably the result of getting banged on the head while they were babies). By early 1997, a psychologist at the University of Texas Medical Branch in Galveston could conjure up red-and-blue reconstructions of the brains of violent offenders and use them to support his view that their hair-trigger tempers were the result of an impairment of the frontal and parietal lobes of their brains.
Neuroscientists have isolated and begun to study the roles of several neurotransmitters in suicidal patients, depressives, and people prone to impulsive violence. They have connected both excesses and insufficiencies of serotonin and dopamine with impulsive violent behavior and with diseases of the brain such as Parkinson’s. At the same time, the mapping of the human genome is providing pictorial representations of where our genes reside in relation to one another. We can now see our genes as strings of beads, and it seems only a matter of time before the bad bead on the string will be correlated with the suspect area in the brain scan.
Among the most interesting studies in progress is a project at Brookhaven National Laboratory on Long Island linking dopamine, cocaine addiction, the rise of euphoria, and subsequent violent behavior. The research seems to indicate that people who do not produce enough dopamine-- whether through a genetically encoded trait or from some environmental cause--might seek out addictive drugs to avoid feeling depressed. Whatever the cause, brain scans of recovering addicts show damage in parts of the brain that neurologists have identified as controlling acceptable interpersonal behavior. Other studies have focused on the role of serotonin in aggression. Researchers at ucla observed a colony of vervet monkeys whose social structure they could manipulate by controlling serotonin levels in individual animals. High levels raised the status of male monkeys in the hierarchy of the colony, and high status goes with dominant behavior.
Both scientists and popularizers have predicted that the new behavioral genetics will lead to the kinds of therapies and cures that medical genetics hopes to achieve for physical disease. Yet for all its sophistication and, in some cases, caution and care, the new biology of violence is at risk for many of the difficulties that have afflicted the entire field of human behavioral biology since the early decades of this century. Researchers continue to find it difficult to eliminate or compensate for environmental influences in their studies. For instance, putting together a control group of families that have the same complicated situations as a subject group is an inexact process, to say the least. Controlling for the existence of, say, poverty is relatively straightforward, but controlling for a family’s attitude toward its own poverty--and attitude will have a big impact on how well family members cope with it--is practically impossible.
Many theories also suffer from imprecise definitions of the traits they purport to explain, or they lump disparate behaviors together-- such as putting all manifestations of violence under the catchall category of aggressiveness. These call to mind Charles Davenport’s efforts to find genetic explanations for nomadism, shiftlessness, and thalassophilia- -a love of the sea that he discerned in (male) naval officers and concluded must be a sex-linked recessive trait. Contemporary scientists have attributed to genes the propensity to crave thrills, to have leadership qualities, to be unhappy, to divorce, and to wear a lot of rings (or beringedness, as one psychiatrist calls it). Researchers from City of Hope, the Duarte, California, research hospital, declared that the D2 dopamine receptor gene was associated with an entire constellation of destructive behaviors, including autism, drug abuse, attention-deficit hyperactivity, post-traumatic stress disorder, pathological gambling, Tourette’s syndrome, and alcoholism.
The new biology of violence has often drawn excellent correlations from studies with animals, particularly mice and monkeys. But what animals have to tell us about human behavior is severely limited. It is difficult to see how the sex lives of adolescent mice, for instance, has much at all to do with our sons and daughters. When a male rodent mounts a female, and the female assumes an accepting position, they are not doing so as a result of social pressures: both animals are acting according to biological signals alone. It doesn’t take a Ph.D. to know that such is not the case with boys and girls. Monkeys, on the other hand, are certainly behaviorally closer to humans. After all, they undergo many of the same developmental stages, and anyone who has watched adolescent vervets knows that they sometimes act a lot like college students the week after exams. But monkeys are not people by any measure.
Despite all that neuroscientists have learned about brain chemistry and structure, they in fact still know very little about how the brain works, let alone how it governs action. Much confusion over research on the biology of violence occurs because the public does not always appreciate the largely correlational aspect of the research. Scientists in general cannot yet say that a specific abnormality in the brain causes a person to exhibit a particular violent behavior; they can say only that the two tend to occur in the same individual. Although in some cases an abnormality may indeed be said to cause a behavior, it is sometimes equally plausible that a behavior causes an abnormality. Further muddying the waters is the obvious and unenlightening fact that all behavior--even learned behavior--is in some sense biological. We initiate a biological process every time we use a finger to press a button or pull a trigger. The biological activity that scientists observe can often be the result of our experience in life or even pre-life in the uterine environment. Researchers are still a long way from predicting, much less preventing, most outbursts of violence.
Meanwhile, even the hope of using biology to foretell an individual’s tendency to violence poses grave difficulties for a democratic society. The prospect strikes directly at conventional notions of human dignity and freedom. If we could tell that someone has a 65 percent chance of behaving violently if he consumes alcohol, how should that information be used? Should it be made public, thus stigmatizing the person? Should legislation be passed making it illegal for such people to drink? Since the advent of the xyy research, many have worried that screening children for biological propensities to violence could lead to a self-fulfilling prophecy. Telling children that they are prone to violence might just encourage them to meet those expectations.
Another difficulty arises from the not unreasonable notion that if biology is destiny, then responsibility becomes moot--a point not lost on defense lawyers. In 1982, John Hinckley, who shot Ronald Reagan and James Brady, was sent to a mental hospital instead of prison in part because a jury accepted ct scan evidence that he was suffering from shrunken brain and had therefore not been responsible for his actions. While brain scans have not been used successfully to exculpate murderers, they have been employed to avoid the death penalty, and in the last several years criminal defense lawyers have proposed that a deficiency in the enzyme that regulates serotonin might make a good legal defense.
We would probably all like to cure society of violent behavior with something akin to a vaccine to prevent its spread and an antibiotic to cure what we already face. But the medical analogy gives undue weight to the biological basis of the behavior. We know what causes violence in our society: poverty, discrimination, the failure of our educational system, says Paul Billings, a clinical geneticist at Stanford. It’s not the genes that cause violence in our society. It’s our social system. We need better education, nutrition, and intervention in dysfunctional homes and in the lives of abused children, perhaps to the point of removing them from the control of their incompetent parents. But such responses would be expensive and socially controversial. That we are searching, instead, for easy answers in the laboratory is a sign of the times.