THE MURDERER NEXT DOOR: Why the Mind Is Designed to Kill, David M Buss


Every breath we take we owe to our ancestors-an unimaginably long and unbroken line of forebears who managed to survive all of the Darwinian �hostile forces of nature.� We tend to think of evolutionary competition as the �survival of the fittest,� as the struggle of animals to survive the challenges presented by a harsh environment. Those who failed to find food or avoid predators, those who succumbed to disease or became riddled with parasites, hit the evolutionary dust. This much is obvious.

What is less obvious is that the process of evolution by natural selection is played out through generations, and the key to the long-term outcome is reproductive competition. The winners in evolutionary terms are not only those who themselves survive, hut those who manage to reproduce most successfully: those who have the most heirs who are healthy and go on to have heirs of their own. This competition to reproduce successfully is a key driving force in our lives, and the competition can he quite fierce. In each generation, there are a fixed number of reproductively viable women and men available to mate with. The dating market makes it quite clear that some mates are much more desirable than others. As the saying goes, all the good ones are taken. Each man and woman is ultimately in competition with other men and women for �shares� of the ancestry of the next generation.

We are all obviously descendants of those who succeeded in this reproductive competition. As the descendants of those who succeeded, we modern humans carry with us the remarkably beneficial components of body and designs of mind that helped our ancestors prevail.

The fierce evolutionary competition that has shaped us leads, if we will follow, to a theoretical insight both subtle in nature and profound in implication. Analysts of human nature have either failed to recognize it or have recoiled from its disturbing implications. In the intensely competitive game of reproductive competition, through the eons murder has been a remarkably effective method of achieving evolutionary success. Of course, as we became civilized, all human societies developed laws against murder, and in our contemporary lives, murdering carries the threat of harsh punishment. So murder is now a more costly strategy for defeating mating rivals than it must have been in our distant past. Through the long years of human evolution, however, killing would have been a highly effective means of vanquishing rivals and ensuring that the mate we selected passed on our genes and not another�s. From a man�s perspective, killing a rival�s mate strips him of an invaluable and possibly irreplaceable reproductive resource. Killing his children can snuff out his genetic future entirely. Vanquishing an entire group of rivals through mass murder or genocide opens new vistas for the killers and their children to flourish.

It may seem coldhearted to talk about killing as adaptive or murder as advantageous, but if we consider the nature of reproductive competition humans have faced over the long time spans of our evolution, then we can appreciate just what an edge in that evolutionary competition killing would have provided. The benefits of killing, in an evolutionary sense, must be momentous and manifold, because, on the other side, the negative reproductive consequences of being killed are so profound.

No newspaper is likely to carry the headline �Scientists Discover That It�s Bad to Be Dead.� We know this. Getting murdered, however, turns out to be far worse, evolutionarily, than we have probably realized.

Bear with me as I play out the many aspects of this critical insight. To start with, being killed cuts off all avenues for the unfortunate victim�s genes to be passed on. Never again will a male homicide victim court, attract, or seduce another woman. Never again will the victim make love with his wife. All potential sexual encounters with strangers, all potential liaisons with mistresses, are forever terminated. Every future act of mating, and hence every future opportunity for reproduction, is permanently extinguished. But that�s merely the beginning.

The victim�s wife, if he has a partner, now becomes eligible for mating with other men. No longer can the dead man fend off former friends or current enemies who attempt to charm her. Another man may now sleep in his bed, caress his wife�s skin, and impregnate her. All of his mating losses become potential reproductive gains for other men. But the costs of getting killed get worse still.

The homicide victim�s children now become frighteningly vulnerable. The victim is no longer around to help raise them and see them through life�s countless hurdles. He can no longer protect them from beatings, sexual abuse, or homicide at the hands of strangers or stepfathers. His children also risk losing his wife�s parental attentions if she remarries, which may get rechanneled to children she has with her new husband.

To compound these costs, given the calculus of evolutionary competition, the murder victim�s losses become potential gains for eager competitors. His elimination from the status hierarchy opens a niche for a rival to ascend. The children of his antagonists will thrive in competition against his children, who now become hampered by their father�s death. His entire kin group is weakened and made vulnerable by his death. In short, the costs of getting killed cascade to one�s children, grandchildren, great-grandchildren, and the victim�s entire extended family: Simultaneously, the victim�s costs become his rival�s benefits in this ruthless competitive struggle. The eternity of darkness that comes with premature death may he accompanied by the abrupt end of an entire genetic line.

If this view of the competitive motives behind human nature seems severe, consider the following story from a study of the Ache Indians of Paraguay, South America, one culture that may provide a glimpse into what our ancestral culture was like.

Among the Ache, meat is a scarce and prized resource. Although gathered berries, nuts, and plant foods are shared only within families, the Ache share meat from the hunt communally. Hunters deposit their kill to a central �distributor,� who then allocates portions to different families, based largely on family size. Good hunters enjoy great status, and groups strive to keep good hunters happy, but, surprisingly, skilled hunters do not garner a larger share of the communal meat. They benefit from their greater-than-average contributions in two ways. First, the group provides extraordinary health care and solicitude to the children of good hunters. These children enjoy being groomed and tended-group members take the time to feed them, remove splinters from their feet, and nurse them to health when ill. Second, skilled hunters are highly attractive to Ache women. It�s not uncommon for an accomplished hunter to indulge in a mistress or two on the side. These benefits, however, cause conflict.

One day a fight broke out between two Ache men, a skilled hunter and an average hunter. The conflict arose over a woman-a sexual infidelity discovered by the less adept man, who challenged his rival to an ax fight. The husband lost; he ended up dead, felled by the blade of his more athletic rival. Within a matter of days, the group convened to decide the fate of the dead man�s thirteen-year-old son. The fact that he now lacked a father meant that he would he a net drain of resources on the group. The group made a decision. The dead man�s son must die. The death of the father, in short, caused the group to kill the son. There�s a lesson here-dead men can�t protect their children. This case starkly demonstrates the costs of murder for the victim�s kin.

So it�s astonishingly bad to be dead. And on the flip side, it�s also astonishingly advantageous to get a rival out of the way. Consider just a few of the specific benefits our ancestors could have secured by killing other human beings:

* Preventing injury, rape, or death to oneself, spouse, or kin

* Eliminating a crucial antagonist

* Acquiring a rival�s resources or territory

* Securing sexual access to a competitor�s mate

* Preventing an interloper from appropriating one�s own mate

* Cultivating a fierce reputation to deter the encroachment of enemies

* Avoiding investment in genetically unrelated children (stepchildren)

* Protecting resources needed for reproduction

* Eliminating an entire lineage of reproductive competitors

Of course, many of us never come close to killing someone, and that�s true for several reasons. One is that, as we�ve become more civilized as a species, we�ve developed more and more effective deterrents against murder, both through our legal systems and through our cultural conditioning-though, as we found in our study of homicidal fantasies, most of us do contemplate the idea of murdering at some point in our lives. Another force inhibiting us from committing murder comes from our evolutionary heritage. As the motivations to murder evolved in our minds, a set of counter-inclinations also developed. Killing is a risky business. It can be dangerous and inflict horrible costs on the victim. Because it�s so had to he dead, evolution has fashioned ruthless defenses to prevent being killed, including killing the killer. Potential victims are therefore quite dangerous themselves. In the evolutionary arms race, homicide victims have played a critical and unappreciated role-they paved the way for the evolution of antihomicide defenses.

Thanks to these antihomicide defenses, it�s often far too costly to kill. In attempting to kill, you become vulnerable yourself. The intended victim�s friends and relatives might rush to his defense. From the killer�s perspective, even if he survives and succeeds in carrying out the kill, he risks ostracism or banishment. We usually don�t want killers in our midst, and neither did our ancestors, although in a confrontation with a hostile group, killers come in quite handy.

That we have such a rich repertoire of defenses against killers actually provides compelling evidence that murderers have been among us for a long enough time to have sculpted the human mind. just as our prominent fears of snakes betray an evolutionary history in which snakes posed a hostile threat to survival, our well-honed defenses against murderers reveals an evolutionary history in which homicidal humans have threatened survival.

Because of the deterrents and the dangers involved with murder, most potential killers opt for alternative solutions in contending with a rival. One strategy is to form alliances with others in a group-a tribe, a social group, at the workplace-attempting to form a critical coalition to oust the rival. A second is to befriend the rival, currying his favor, making him part of your coalition. A third is to denigrate the rival to others in an attempt to lower his reputation in their eyes, weakening his position and making him more vulnerable to displacement. A fourth strategy is to lie like a snake in the grass, hiding your time until a rival stumbles, and then making your move. And as you bide your time, a rare opportunity may arise. You may suddenly find all the stars aligning in a unique configuration. The costs of killing unexpectedly dwindle; the benefits abruptly loom large. Perhaps you happen upon your rival alone and unawares. Perhaps you can kill without being discovered. Perhaps you can actively arrange to create all of these conditions. You suddenly find yourself with the means, the motive, and the opportunity. And you seize the moment. Your psychological circuits for homicide become engaged.

Let�s step away from our own species for a moment so we can be more objective, and examine our close primate cousins the chimpanzees. Chimps and humans diverged from common gorilla ancestors roughly seven million years ago. Nonetheless, humans and chimps share roughly 99 percent of their genes. This means that, of the three billion base pairs strung out on the strands of our DNA, as many as ninety-nine out of every hundred are exactly identical. The differences, of course, are as important as the similarities. Humans are bipedal and have evolved language, and women have relatively concealed ovulation. Chimps brachiate (travel from branch to branch through trees) and communicate without language, and the females have periodic estrus with bright red genital swellings visible from a hundred feet. Nonetheless, because they are our closest primate relatives, observing their behavior can sometimes shed light on our own.

Consider an observation by anthropologists who were following a chimpanzee troop around the jungles of Tanzania. One sunny afternoon, eight chimpanzees, all males but one, roamed the border of their home range. Although they usually stayed within their home range, perhaps the chimps felt emboldened by the size of their group, protection afforded by numbers. Not far across the border, they detected a lone male. A chimp named Godi sat peacefully beneath a tree, eating ripe fruit in solitude. Godi, a member of the Kahama community, usually traveled with his group of six other males. This day he happened to be alone.

The second he saw the rival group, a jolt of adrenaline surged through his veins. He dropped his food, sprang to his feet, and bolted through the forest in the direction of his Kahama comrades. But the surprise ambush gave his attackers a timely advantage. His pursuers gave chase and surrounded him. In a flash, Godi was captured. Humphrey, one of the lead chimps, grabbed Godi�s leg, yanked him to the ground, and pounced on top of him. Using his full weight of 110 pounds, Humphrey pinned him to the ground. Godi struggled, but was no match for Humphrey and his six male compatriots, each of whom carried the strength equivalent of four Olympic athletes at the peak of conditioning. With Godi rendered helpless on the ground, the others now launched an assault. In a frenzy of screaming, they bit, pounded, and jumped on their helpless victim.

After ten minutes that seemed like an eternity, the attackers finally stopped. They left behind a body battered and bleeding from dozens of wounds. Godi did not die immediately, but he was never seen alive again. The killer chimps had seized a rare opportunity, perhaps one that would not come along again for many months.

We often think of human warfare as formal battles between declared enemies, but in traditional foraging societies, killing more often takes the form of a raid not unlike that witnessed among the chimpanzees. Anthropologist Napoleon Chagnon, who spent years observing the lives of a group of native peoples in Venezuela called the Yanomam�, observed one such raid.

The night before the raid, a man named Kaobawa stirred the men into an emotional frenzy. He began to sing, �I am meat hungry! I am meat hungry!� Another man screamed, �I�m so fierce that when I shoot the enemy my arrow will strike with such force that blood will splash all over ... his household.� At dawn the next morning, the women presented the raiders with a large cache of plantains as food for their raid. The men covered their faces and bodies in black paint for concealment. The mothers and sisters of the warriors offered parting advice, such as �Don�t get yourself shot up.� The women then wept, fearful for the safety of their men. The trek to reach their enemies was long and took several days. At night, the raiding party built fires to keep warm, but on the last night, this luxury had to be eliminated for fear of alerting the enemy.

Back at the home camp, the women grew nervous. Unprotected women risk being kidnapped by neighboring tribes, and even allies cannot be trusted.

The raiding party broke into two groups, each consisting of six men. This grouping allowed them each group would lie in wait toto retreat under protection: two men from to ambush potential pursuers. They struck. The attacking party managed to shoot one of their enemies with a poison-tipped arrow. The raiders then fled. One of the raiders was wounded as they escaped to their home camp, but he survived to go on a future raid. The foray had been a success. They killed one member of the enemy group and escaped with their lives, just like the chimps of Tanzania.

Killing, of course, is ordinarily not a first-line solution, even when your own life is on the line. When threatened by a weapon-bearing intruder who has broken into your home, you would be as likely to hide or flee as to go on the attack. The ancient phrase �fight or flight� captures two of the most important defenses available to us. The shields we�ve developed to stop killing have evolved alongside the mental mechanisms that provide the impulse to kill. Unfortunately, the process of coevolution, whereby new adaptations have developed to counter those defenses, has created a vicious cycle from which there is no escape. Even as we�ve developed defense mechanisms, we�ve also developed ever-more-effective means of killing.

Typically, coevolutionary arms races occur between two different species of which one is predator and the other prey, or between parasites and hosts. As predators pick off slower and less agile prey, the remaining prey and their descendants evolve to be faster and more skilled at evading capture. Then the prey�s improved evasion abilities create greater selection pressure on the predators-the slow predators fail to eat and so die off, and the faster ones give birth to a higher percentage of speedy progeny. Each increment in the skills of one species leads to increments in the abilities of the other. The two species are locked in an endless escalating cycle from which neither can escape.

Coevolutionary arms races also occur within a single species, and this remarkable process has occurred in our species with the evolution of homicide strategies and murder-prevention defenses. As natural selection fashioned defenses against getting murdered by other humans, it simultaneously created more intricate killing strategies to evade these defenses. As potential victims evolved to detect homicidal intentions, potential killers evolved the ability to deceive and surprise victims, to disguise their homicidal designs. Our ancestors evolved to live in groups that afforded defense against marauding males. At the same time, they evolved recruitment tactics designed to increase the size of their killing coalitions.

One time-honored recruitment tactic for increasing coalitional size that we�ve read about in the news lately is to exploit men�s desire for women. Mohamed Atta, one of the main architects of the 9/11 terrorist attacks, was unlucky in love. His recruiters instilled in him the belief that he would spend his afterlife surrounded by �women of Paradise� (from an assassins� manual found in Atta�s luggage), �youths of never-ending bloom,� and �companions with big beautiful eyes like pearls within their shells . . .� (from the Quran, about the rewards of becoming a martyr). The promise of prestige and the pledge of young women are powerful methods of coalitional recruitment. From the inner-city gangs of New York and Los Angeles to religious jihads, men are motivated to kill to gain these rewards. A relentless coevolutionary arms race in the human struggle for life, liberty, and the pursuit of progeny continues today.

Can this evolutionary-competition theory of murder really account for the motivations for murder in our present timesAs I will reveal in the rest of the book, this theory does a remarkable job of accounting for the statistical patterns we find in who kills whom and for the multiple motives for murder. The more I analyzed the psychology of killing in cases of actual murder and in homicidal fantasies, the more striking was the realization that so many murders follow from the intense pressures of mating-a topic explored in the next chapter.