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  Medicine and science have evolved several strategies to help unskein the effects of heredity from influences of the environment: family studies, which examine familial patterns of suicide and suicide attempts; twin studies, which look at rates of suicide in identical and nonidentical twins; adoption studies, which are designed to tease apart “nature-nurture” issues by comparing suicide in adopted individuals with suicide in their biological and adopted relatives; and molecular genetic studies, which look at alterations in specific genes in individuals who do and do not commit suicide. Each of these strategies gives us a different kind of information.

  There have been more than thirty family studies of suicide, and almost all of the ones completed in recent years find a greatly elevated rate of suicide and suicidal behaviors in the family members of those who commit suicide and those who make a serious attempt. In studies of children and adults, as well as in studies of patients with psychiatric illness, those who commit suicide are at least two or three times as likely to have a family history of suicide as those who do not. Individuals who commit or attempt suicide in a violent manner—by gunshot, hanging, or jumping—are particularly likely to have a strong family history of suicide, often of violent suicide.

  One of the most important and interesting of the family studies of suicide was carried out by Janice Egeland and James Sussex in their work with the Old Order Amish, a conservative Protestant religious sect that settled in southeastern Pennsylvania in the early eighteenth century. The community is agrarian, socially cohesive, and protected against many of the risk factors that ordinarily permeate urban culture. Alcohol is prohibited; serious crime is essentially nonexistent; and loneliness and isolation are relatively unusual due to the emphasis on extended families living together in the same homes. Social support is exceptionally strong, and unemployment is not a significant problem. Suicide—known by the Amish as “the abominable sin” or “that awful deed”—is socially unacceptable and strongly censured by the community; until recent times, Amish who killed themselves were buried outside the boundaries of the community cemetery.

  The Amish have kept extensive genealogical and medical records of their ancestors that extend back through thirty generations; because of this, Egeland and Sussex were able to identify all of the suicides that occurred during the hundred-year period between 1880 and 1980. Twenty-five of the twenty-six confirmed suicides (92 percent) were diagnosed with depression or manic-depression (of necessity, some of the symptoms of mania were culturally bound and included, in addition to the more traditional diagnostic criteria, “racing one’s horse and carriage too hard … buying or using machinery or other worldly items … excessive use of the public telephone”), and most were situated in families that had, for many generations, been suffused with mood disorders. Twenty of the twenty-six suicides were by hanging, four by gunshot, and two by drowning. Most of those who killed themselves were married with children, and most were in the prime years of their life.

  The most dramatic and scientifically interesting finding in the Amish study of suicide was the extent to which the suicides clustered in only a few families. Just four families accounted for 73 percent of all suicides; these, in turn, made up only 16 percent of the total Amish population. The suicides clustered in families with mood disorders, but most families with heavy loadings for mood disorders did not show a heavy concentration of suicides. This tendency for suicides to cluster in some families heavily loaded with depression and manic-depression but for there to be many with mood disorders and no suicides was later replicated in an Austrian study.

  The evidence from family studies is suggestive of a genetic influence on suicide but it is not conclusive. A clustering of suicides in a family may be due to other, nongenetic factors as well: a child whose parent kills himself may suffer extremely from the loss and, if inclined to depression, respond in a desperate and similar way; exposure to violence or suicide may have a particularly deadly impact upon some family members; or suicide may be imitated or learned as the seemingly best solution to severe pain, privation, or stress. One way to tease out environmental and psychological effects from genetic ones is to look at the rates of suicide in identical and nonidentical twins.

  Identical twins come from the same egg and therefore share the same genetic material. Nonidentical twins, on the other hand, come from two eggs and share only half their genes (in this sense, they are no different from their other siblings). If genetic influences are present, one would expect a far higher concordance rate for suicide—that is, if one twin commits suicide, the other does as well—in identical twins than in nonidentical ones. This turns out to be true.

  Alec Roy, a psychiatrist at the Veterans Administration Hospital in New Jersey, has written more about the genetics of suicide than anyone else. He recently reviewed all of the twin studies published in the psychiatric literature and found nearly four hundred pairs in which at least one twin had completed suicide. Of the 129 identical twin pairs, 17 committed suicide, and of the 270 nonidentical pairs, only 2 did. This, from a statistical point of view, was a highly significant difference. In a different study, of attempted suicide, Roy found that nearly 40 percent of identical twins whose co-twin had committed suicide themselves attempted suicide; no surviving nonidentical twin did so. Recent research from Australia found likewise: if one identical twin made a serious suicide attempt, nearly 25 percent of the co-twins did as well; none of the nonidentical twins did. The authors noted that although it could be argued that identical twins share a closer psychological and social world than nonidentical ones—they are, for example, more likely to dress alike and be treated in a similar manner—the social and psychological closeness between nonidentical twins was also very strong.

  The concordance rate for suicide in identical twins, approximately 15 percent, suggests several things. First, although the rate is much higher than it is for nonidentical twins, it is not formidably high. Even in individuals who are genetically most similar, the odds are overwhelming that if one identical twin kills himself the other will not. Second, the concordance rate for suicide in identical twins is far less than the concordance rate observed for manic-depression (70 to 100 percent, depending on whether suicide and recurrent depression are included as concordant diagnoses), or schizophrenia (40 to 50 percent). The genetic influence may simply be stronger in the severe mental illnesses than it is in suicide. It is also possible that the devastating impact of suicide on the surviving twin actually lessens the chances that he or she will commit suicide, either because of a heightened awareness of the psychological pain caused to others or because the twin is now more apt to seek out and receive medical care.

  The findings from the twin studies provide strong evidence for a genetic effect, but family dynamics and other psychological issues inevitably confound their interpretation. One way of further isolating environmental from genetic influences is by conducting an adoption study. Individuals who are adopted share their genes, but not their environment, with their biological parents; conversely, they share their environment, but no genes, with their adoptive parents. Adoption therefore creates a unique natural experiment. If there is a significant genetic influence on suicide, one would expect a much higher rate of suicide in the biological parents of adoptees who commit suicide than in the adoptive parents. This is exactly what was found in two studies done in Denmark, a country that for years has maintained excellent and comprehensive medical records.

  The first study, based on all Copenhagen adoptions between 1924 and 1947, revealed that fifty-seven of the adoptees eventually committed suicide. These fifty-seven adoptees were matched with a control group of other adoptees for such factors as age, sex, social class, and the amount of time spent in institutions or with their biological parents. An extensive examination of the causes of death in biological relatives established that twelve of the biological relatives of the adoptees who committed suicide had also committed suicide; only two of the biological relatives of the adoptees who had not committed
suicide had killed themselves (this was a highly significant statistical difference). None of the adopting relatives of either the suicide or control group committed suicide. Although the authors of the study found that only six of the twelve biological relatives who committed suicide had had any contact with psychiatric services and therefore concluded that the genetic predisposition for suicide may, at least to some extent, be independent of major psychiatric disorders, this may or may not be true. In the United States, for example, more than half of those who meet the diagnostic criteria for mood disorders never seek or receive psychiatric treatment.

  In a second study of Danish adoptees, seventy-one adoptees were identified as having suffered from a mood disorder. They were then matched with seventy-one adoptees who had no history of psychiatric illness. Fifteen of the nineteen suicides that occurred in the relatives of the two groups of adoptees occurred in the biological relatives of the adoptees suffering from depression or manic-depression. The rate of suicide in biological relatives was especially high in adoptees who had a strongly impulsive quality to their depressive episodes.

  Together, the family, twin, and adoption studies make a strong case for a strong genetic influence on suicide and suicidal behaviors. Genes are, of course, only a part of the tangle of suicide, but their collision with psychological and environmental elements can prove, as we shall see later, to be the difference between life and death.

  If suicide has a genetic underpinning and the illnesses most associated with it—depression, manic-depression, schizophrenia, and alcoholism—have even stronger ones, it is natural to ask why—with all their pain, maladaptiveness, and early death—they should survive in the gene pool at such high rates. Is there any evolutionary reason for suicide, or is it simply random splicings of and realignments in DNA? Is it the result of a deadly interaction between a stressful world and vulnerable wiring, or is there some common element that drives both life and death? Is suicide always conscious and therefore a uniquely human behavior, or do we share with other animals the capacity for self-destructiveness and the deliberate ending of life? How, in short, does suicide fit into and serve the rest of the natural world?

  The construing of suicidal acts as consciously determined and therefore uniquely human is both obvious and problematic, as psychiatrists Ivor Jones and Brian Barraclough point out:

  Suicide poses a special problem in relating animal studies to man: man can visualize his death and arrange it, no animal has ever been shown to do that. In this sense suicide is uniquely human. However, this formulation implies that the processes leading to suicide are rational, which may be untrue: depression in most suicides probably impairs the capacity for rational thought while at the same time inducing suicide impulses. We suggest that suicide may be a uniquely human attribute only because our definition of it makes it so; in other words, if suicide were to be defined as a destructive act inflicted on the self leading to death, then animal analogies do exist. However, even by this changed definition, man’s suicide and animal self-destruction are different in the following ways: Man may defer the event, the animal does not. Man may use an instrument, the animal does not. Man may manipulate his environment to do the act for him, the animal does not. It seems, therefore, that if animal behaviour is relevant to suicide it provides only one component—a disposition to self-injury—which becomes incorporated into a syndrome with other uniquely human components.

  No one disputes that some animals under conditions of acute stress—isolation, overcrowding, confinement, alterations in habitat—inflict great damage, even death, upon themselves. They may gnaw through their limbs or tails, gouge out their eyes, otherwise mutilate their bodies, or ceaselessly bang their heads against the walls of their enclosure. Severe self-inflicted injuries and death from stress have been reported in many zoo animals, including deer, lions, hyenas, and jackals; in a variety of captive primate species; in mice, rats, octopi, opossums, platypuses, and numerous other animals; and in domestic pets when separated from their owners. Macaque monkeys will slap and bang their heads and use their teeth and claws to gash their limbs and body. On occasion, domestic pigs and some wild animals, when captured or transferred to new environments, make violent attempts to escape; if unable to get away, a few fall into a stupor. Many ranch mink chew through their tails when kept in captivity.

  The most severe forms of self-injury in animals seem to occur when a confined animal or an animal reared in isolation encounters acute stress; this in turn typically precipitates an agitated, aggressive, or frustrated state. “In all known instances,” Ivor Jones says, “the severe class of self-injury and some headbanging is associated with acute agitation.” The agitation and frustration appear to arise from limitations in the type and extent of physical activity, alterations in or elimination of usual feeding and grooming behaviors, or a lack of social or sexual contact with other animals. Acute agitated states can also be induced surgically or pharmacologically by creating lesions in the brain or by administering drugs and alcohol.

  To some extent, self-injurious behavior in animals substitutes for the aggression normally directed at other animals or energy that would otherwise be expended in coping with the natural world. Self-injuries also seem reduce the level of acute agitation experienced by the animal, in a way not dissimilar to the defusing of tension that allows self-mutilative or cutting behavior in humans who suffer from particular forms of psychopathology (such as borderline personality disorder). Severe social isolation and confinement in humans, such as that experienced by prisoners, can lead to analogous destructive behavior. Prisoners, for example, have amputated their toes, fingers, and genitals; occasional disembowelings have also been reported.

  Overcrowding in the wild also often results in behaviors that end in injury or death for an individual animal. Rats, when too populous for the environment in which they find themselves, exhibit grossly abnormal behavior: aggression increases precipitously, as do premature deaths; fertility declines in adaptation to dwindling resources; and maternal behavior, including nest building, suffers. Cannibalism occasionally erupts, as it does in frogs and alligators and other species when they become too densely populated. Snowshoe hares, even when removed from overcrowded spaces and placed in safe environments with plenty of food and water, often die from stress and refusing to eat. Prolonged psychopathology is rarely observed among animals other than humans, because, as primatologist Henry Harlow and his colleagues point out, such animals do not survive very long in the natural world.

  Lemmings, the poster animals for suicide, do not in fact commit suicide. They do, however, abandon highly populated areas, and in the course of their migrations to new, less densely populated sites, many die. Their deaths are an inevitable price of their travels to new lands. This dispersal of animals, which both extends their territorial range and ultimately increases their genetic diversity, is advantageous to the species but not necessarily to the individual: the lemmings’ “suicidal march to the sea” is in no meaningful sense suicidal.

  Animals engage in risky behaviors other than emigration to new territories. Years ago, Harvard biologist E. O. Wilson set out the case for “altruistic” behaviors, demonstrating that some animals sacrifice their own shelter or food to close kin. The enhanced survival of kin in turn makes more likely the survival of the family genes. In social insects, for example, protection of the group by soldier wasps or ants may bring death to the individual but, through that death and others, allow the group to survive. Animals that travel in herds, such as bison or elk, often protect their young by surrounding them with older and stronger members of the group. The mountain gorilla, which travels in a small social group, uses subordinate males to protect the infants and females. These animals, which stand guard at the edges or position themselves between predators and the group’s most vulnerable, are necessarily at risk of injury or death.

  Within most species, including humans, there is a range in the ability and willingness to take such risks. Temperaments and capacities vary.
Some animals move faster and are more curious, more impulsive, more restless. Highly energetic, grasping, and aggressive, they are drawn to new regions, different foods, and disparate mates. Others wait, stand back, move collectively, and act less impetuously. The diversity of styles and temperaments serves the needs of the group, allowing it, as necessary, to push forward, or pull back, or to expand or conserve its collective energies.

  Like other animals, human beings are diverse in their capacities and temperaments. Adaptive behaviors lurch with dispatch into maladaptive ones, a perhaps inevitable price that must be paid for a biological system that maintains the capacity to ratchet its responses—flight, aggression, cooperation—rapidly to survive in a changing or dangerous environment. The balance between adaptive and pathological is often a tottery one, and it makes evolutionary sense that it should be so. George Schaller observed in his studies of the Serengeti lion and its prey that “a galloping animal is precariously balanced”: speed is necessary to save life but carries with it the risk of losing it.

  Aggression, likewise, is subject to jeopardous overshoot. “We are strongly predisposed to slide into deep, irrational hostility under certain definable conditions,” writes E. O. Wilson in On Human Nature. “With dangerous ease hostility feeds on itself and ignites runaway reactions that can swiftly progress to alienation and violence. Aggression does not resemble a fluid that continuously builds pressure against the walls of its containers, nor is it like a set of active ingredients poured into an empty vessel. It is more accurately compared to a preexisting mix of chemicals ready to be transformed by specific catalysts that are added, heated, and stirred at some later time.” Human beings, he continues, “are strongly predisposed to respond with unreasoning hatred to external threats and to escalate their hostility sufficiently to overwhelm the source of the threat by a respectably wide margin of safety.”