IN THE COURSE of this book, we have looked at the murderers who are all around us, from the man whose honor was insulted to the woman who sees killing as the only way out. Murder affects the lives of all of us. Have you ever felt the hair stand up on the nape of your neck when a dangerous-looking man comes into your midst? Have you felt the eyes of a stranger watching your every move and forced yourself not to jerk your head up to assess his intent? Has anyone you know ever been murdered? Have you ever thought about killing someone? Killers are all around us. They are you and me. They may be in the next room, the next house, or the next neighborhood. It matters not where you live. There is no safe place on earth.

Nearly everyone has felt grave danger at some point, sensing that someone had a motive to murder. We will never know how many of us are alive today because a menace threatened and we acted to escape from it. But we do know, based on the reports of thousands of participants in our studies, that most of us have acted when we suspected a potential murderer in our midst—avoiding the dangerous stranger, fleeing a sexual predator, running from an angry rival, hiding from an ominous enemy, securing weapons of self-defense, seeking the protective haven of close kin, or clinging to our closest friends.

Over deep time, evolved defenses kept killing in check. But they have also had the unfortunate consequence of creating more subtle, refined, and sophisticated homicidal strategies designed to circumvent defensive armaments. The perpetual coevolutionary arms race continues today, with each new adaptation in the murdering mind creating corresponding counter-adaptations to prevent people from ending up dead. At this moment in time, all of us are end products of the relentless coevolutionary process.

People have been murdering other people at appalling rates for thousands, probably millions, of years. Psychologists, psychiatrists, sociologists, criminologists, and anthropologists have devoted great effort in the last century to understanding why we kill. In the course of my research, I became convinced that the previous theories simply don’t work. The social-learning theory of media violence advocated by leading aggression researchers Rowell Huesmann and Len Eron can’t explain why killing is more common in cultures lacking television, movies, and violent video games. It cannot explain why the Yanomamö, Jivaro, Mae Enga, Dugum Dani, Gebusi, Maori, the supposedly peaceful Polynesians, and hundreds of other tribal peoples, using simple hand-fashioned weapons like wooden clubs and bows and arrows, have historically murdered at higher rates than their gun-toting, video-watching American peers. The child-abuse and pathology theories advocated by Richard Rhodes in Why They Kill and Jonathan Pincus in Base Instincts cannot explain why perfectly normal next-door neighbors with no apparent evidence of psychological abnormalities—people like Susan Smith, Clara Harris, Kristofer Marsh, Diane Zamora, Diane Downs, Jean Harris, Susan Wright, and thousands of other killers like them—commit murder.¹

We must come to grips with the unpleasant reality that murder has been a remarkably effective solution to many of the challenges we’ve faced in the evolutionary trials of survival and reproductive competition: ascending social hierarchies, creating a reputation that deters encroachers, protecting and keeping our families, escaping from violently abusive relationships, gaining access to new lovers, and many others we’ve encountered along the way in this book. The vast majority of people experience thoughts of killing in precisely the circumstances in which homicide has been an effective means for solving these problems—an enormously improbable coincidence if the mind were not designed for murder. People believe their lives are most in danger from their fellow humans in exactly the same circumstances, again a statistical improbability if humans over eons had not confronted murderers in their midst in these conditions. Our moral abhorrence of homicide should not cause us to reject the compelling evidence that a deep psychology of killing has been and is an essential component of human nature.

Previous myths about harmonious peoples living in a pacified past have been shattered.² As we saw in the first chapter, the bioarcheological evidence of graves filled with skeletons embedded with arrow tips and damaged crania betrays a long history of killing. Modern humans have descended from ancestors who murdered. And they didn’t just kill one at a time. In perhaps the most disturbing development in this history of the human species, we evolved adaptations to murder en masse.

NATURAL-BORN KILLERS

In anthropological accounts of tribal warfare we find powerful evidence that killing raids have historically been a strategic means of winning the merciless competition for survival and reproduction. The spoils that have traditionally flowed to the victors in warfare do not surprise us now—territory, food, water, weapons, and women.

Consider, for example, the case of the ancient Maori culture of New Zealand. On a recent research trip across the globe to study homicide among these original inhabitants of New Zealand, I acquired a Maori war club. These war clubs are called generically patu, with subvarieties such as the mere, which is the one I acquired. Although only two feet long, the mere is surprisingly heavy. Gripping it as the ancient Maori did imbues one with an eerie sense of power.

Maori warriors primarily targeted enemy men for death. They also killed some children and forced others into slavery, but young women were routinely taken as captives, awarded to victorious warriors. This pattern is seen in a chilling account written down in 1828 by a missionary in New Zealand, of a Maori warrior taunting the preserved head of an enemy chief, a practice they reserved for enemies who were particularly detested:

You wanted to run away, did you? but my meri [war club] overtook you: and after you were cooked, you were made [into] food for my mouth. And where is your father? he is cooked:—and where is your brother? He is eaten:—and where is your wife? there she sits, a wife for me:—and where are your children? there they are, with loads on their backs, carrying food, as my slaves.³

Disturbing testimonials to the value of stealing away an enemy’s young women emerge in accounts of tribal warfare all around the globe. Here is an excerpt from one such raid among the Yanomamö of the Brazilian rainforest:

“Raiders!” The scream shook the body of every sleeping Indian. [Deemeoma] jumped from her hammock. The whole shabono [shelter] thundered. She heard a splat. . . . Her mother lay flat on the dirt floor. Blood ran from her mouth. Arrows flew in every direction. Her father was already on his feet shooting back at the enemy warriors. Enemies were everywhere, all around the shabono and still coming in the entrance. Women and children ran to find any place to hide. Most of the surprised warriors were trying to escape.

The bravest, like Deemeoma’s father, never ran. He stood by his hammock, shooting arrow after arrow. He hit an enemy, then another. An arrow struck him in the side but he didn’t even stop to pull it out. He shot until he had no arrows left. Now Deemeoma saw why men had sometimes called him Hard-to-Kill.

Deemeoma was still trying . . . to reach [her father] when the warriors grabbed her. They were just about to kill her when the old warrior shouted, “No! No! No! Don’t kill her. Can’t you see she is healthy? She will bear us many children.” “Not for a long time,” the young warriors objected. They were about to fight. But the old warrior was fierce and respected. “Only kill the boys and the babies and the wounded,” he said. “We have to keep the healthy girls.” He was right and they all knew it.⁴

Seventeen percent of all current Yanomamö wives have been obtained by men abducting them during raids.⁵ Similar patterns emerge among the Tongan Islanders of the South Pacific, according to explorer George Vason, who lived among them for four years beginning in 1796. After the men were killed in battle, some of the women came forward and offered themselves up as prisoners to save their lives: “They became the property of the warrior who first took them. Such female prisoners were seen as an economic investment for their captors, inasmuch as they could be used in such occupations as beating out bark cloth and forming it into ngatu. It was also expected that they would submit to the sexual desires of their owners.”⁶

Statistics bear this out. Among the Dani of New Guinea, for example, 29 percent of adult male deaths result from war. The comparable figure for females is only 2.4 percent.⁷ There is only one reason why men get killed and women get spared in war. Obtaining or holding on to reproductively relevant resources has always been a major motive in war, just as it is a major motive of the murderers next door.

Triumph in battle historically offered the opportunity to enhance men’s status and reputation, which, as we saw in the last chapter, is an extraordinarily powerful drive in men’s lives. In Southeast Asia, dating back to 1000 B.C., according to archeologist Laura Lee Junker, “Raids against rival groups enhanced chiefly status and political sway by providing women for polygynous marriages, increasing agricultural and craft productivity through enslaved labor, and providing sacrificial victims for status-enhancing ritual feasts held by the chiefly elite.”⁸ “Warriors who had undertaken a great number of raids and returned with substantial booty and captives were rewarded with social rank and status insignia. ...”⁹

The glory to be gained by risking one’s life in war has perhaps never been so eloquently evoked as in these famous, stirring words from Shakespeare’s Henry V (IV, iii):

We few, we happy few, we band of brothers;
For he to-day that sheds his blood with me
Shall be my brother; be he ne’er so vile
This day shall gentle his condition:
And gentlemen in England now abed
Shall think themselves accurs’d they were not here,
And hold their manhoods cheap whiles any speaks
That fought with us upon Saint Crispin’s day.

Advances in DNA technology have provided strong genetic evidence that the coalitional killing that characterizes warfare actually works in reproductive competition. Recall the quote earlier by Mongol warrior Genghis Khan, expressing his great pleasure at vanquishing his enemies and sleeping with their wives and daughters. The Khan strategy had profound reproductive consequences. Oxford geneticist Chris Tyler-Smith and his colleagues collected, over a period of a decade, blood samples from sixteen populations from around the former Mongolian empire. In analyzing the DNA of the Y chromosome, they discovered that 8 percent of the men bore a chromosomal “signature” characteristic of the Mongol rulers.¹⁰ This means that an astonishing sixteen million men in that region, roughly half a percent of the entire population of men on earth today, are likely descendants of Genghis Khan. The many sons of Genghis Khan ruled over large territories, and if they followed in the footsteps of their father, they had many wives and large harems. Genghis’s oldest son, Tushi, is known to have sired at least forty sons. Over human evolutionary history, war was a means of driving rival male lineages extinct, with the victorious contributing disproportionately to the descendant population.

In the long history of warfare, we see many of the key motives of the murderer next door played out on a grander scale—competition for reproductively relevant resources; killing to prevent being killed; acquiring status, reputation, and honor; exacting revenge on competitors; vanquishing rival males; murdering the children of reproductive rivals; stealing the women of the conquered men; and exploiting new opportunities for reproduction.

MORAL DILEMMAS

Studies of other species provide an informative context for understanding the evolution of murder. We now know that killing members of one’s own species, contrary to a myth disseminated by the famous ethologist Konrad Lorenz, is in fact widespread throughout the animal world. Among mammals, the tigers, lions, wolves, hyenas, cougars, and cheetahs slaughter their own. Among primates, langur monkeys, chacma baboons, red howler monkeys, savanna baboons, mountain gorillas, and blue monkeys all slay con-specifics. The chimpanzees of Gombe shocked Jane Goodall and those who followed in her footsteps with their horrific chimpicides. Animal researchers no longer doubt that these species possess adaptations to kill their own. This obviously does not prove that humans also have adaptations to murder; each species has its own unique constellation of adaptations. But it does illuminate mammalian and primate designs in which killing evolved, and suggests that there is no reason to be skeptical about the existence of analogous adaptations in humans.

The scientific studies conducted by my lab that I’ve referenced throughout this book have also furnished strong evidence of a mind designed for murder: the statistical analyses of the hundreds of case files of Michigan murders; the detailed homicidal fantasies of thousands of people from the United States to Austria to Singapore to Peru; the studies of death-prevention defenses that reveal a close correspondence between people’s fears of being killed and the conditions under which people actually are killed; the scenario studies, which identified the precise conditions under which people say they would kill; the interviews with homicide detectives and police; the statistical analyses of the massive FBI database of nearly half a million murders; and the widespread cross-cultural evidence provided by biological and cultural anthropologists.

The accumulation of so much evidence coming from so many different data sources, seen in light of the impoverished previous theories that simply cannot explain why people kill in such diverse yet predictable circumstances, must surely give us pause. The burden of proof ought to shift now to those who still doubt that humans have minds designed for murder. We need a radical paradigm shift in how we think about homicide, and it’s time to take off the blinders.

I anticipate that some scholars will react with moral indignation to the theory of the evolved murderous mind. Anyone who proposes that killing is part of human nature surely must be depraved. As an evolutionary psychologist, I’ve become accustomed to critics who confuse what is with what ought to be. When I published my research on men’s evolved desire for a variety of sex partners, for example, some worried that I was condoning, or giving an excuse to, men who cheat on their wives. Similarly, people might mistakenly assume that the theory of adaptations for murder implies approval or acceptance of killing. It doesn’t. I would suggest instead that those who create myths of a peaceful human past, who blame killing on the contemporary ills of modern culture, and who cling to single-variable theories that have long outlived their scientific warrant tread on dangerous moral ground. The problem of murder cannot be solved by wishing away those aspects of human nature that we desire not to exist.

Some might worry that, if we concede that humans have minds evolved for murder, defense lawyers will try to use this as a justification to get their clients off the hook. Yet this “naturalistic fallacy” in reasoning has been exposed as logically incorrect by philosophers decades ago, and I doubt that such arguments would carry much weight in our courts of law. Many things are “natural,” such as diseases and parasites, but we decide that they ought not exist. Death from natural causes in old age is natural—our bodies, to our great misfortune, are built with an expiration date, designed for senescence. But we have decided that we want modern medicine to help us lead unnaturally long lives. That murder comes naturally to humans in circumscribed contexts does not in any way imply we should accept it or excuse it.

Yet another worry stems from the mistaken belief that adaptations for murder imply the inevitability of murder. As I have tried to show throughout this book, murder has evolved as only one among a menu of contingent strategies for solving very specific adaptive problems of survival and reproductive competition. These contingent strategies can, in principle, be activated or deactivated. We have callus-producing adaptations, but can prevent their activation by creating friction-free environments. We can prevent murder, in principle, through a deep understanding of its underlying psychological circuits and designing environments that prevent their activation. The deterrent effect of spending life in a cage, expressed by so many people as the critical factor that prevented them from acting out their homicidal fantasies, shows us that we have influenced the decisions of potential killers.

One of the great ironies of our modern lives is that we carry our killer psychology, so exquisitely adaptive in our evolutionary past, into a modern world where the conditions of our lives have changed so dramatically.

MURDEROUS MINDS IN THE MODERN WORLD

As the many cases recounted in this book have made clear, modern humans have not escaped the challenges of sexual rivalry, mate poachers, abusive partners, or sexual predators. We still struggle to attain status and to save face, and we continue to confront mortal threats at the hands of kin, dangers from stepparents, and even sometimes attacks from gangs of marauding males. The underlying motivations to murder remain prevalent in our lives. Most of us no longer consider murder to be a socially or morally acceptable solution to these challenges, except in highly circumscribed contexts such as defending ourselves, our families, and our friends. And yet we must also contend with the psychological mechanisms that eons of evolution have installed in our brains. We have, as it were, one foot in our ancient past and one in our modern present.

The fact that our modern behavior is driven by ancient evolved mental mechanisms is intriguingly demonstrated by some of the errors in our contemporary assessments of when we are most in danger. One example is our great fear of being killed by a stranger, whereas in fact so many more murders are committed by people we know.

Our ancestors lived in small groups, ranging in size from roughly 50 to 150. As a consequence, every person knew everyone else in the group; there were no strangers among them. Indeed, when a stranger unexpectedly appeared, he was treated with great suspicion, and often killed.

Lacking modern means of transportation, ancestral peoples only ran into those who looked more or less like they did. People who looked different did so by altering their appearance with paint, dress, and body scars. And if they looked different, the odds were greater than chance that they had hostile intentions. Judging by the evidence from tribal cultures of raids and ambushes, attacks by conquering groups killed more than acquaintances within the group. Xenophobia made adaptive sense in the ancestral past.

Our lives in the modern world, with our tremendous geographical mobility and modern urban living, are of course filled with strangers, many of whom are from different ethnic and racial groups. But our psychological circuits have not caught up with this new reality. Our fears of murder are heavily populated with strangers, even though most mortal threats come from people we know. Our research of fears of being killed contain a disproportionate dread of other racial groups. The whites in our sample commonly worried about death at the hands of “this big black person,” “one big black guy,” or “a dark scary man.” The African Americans in our sample, particularly the women, expressed fears of being killed by “white men who are openly racist.” In fact, the overwhelming majority of actual murders occur within racial and ethnic groups. In the United States, 88 percent of white murder victims are killed by other whites, and 94 percent of African American murder victims are killed by other African Americans.¹¹ The expressions of xenophobia are anachronisms whereby a fear of strangers who appear different, so supremely adaptive in the evolutionary past, gets played out mistakenly in the modern world through the ugliness of racial fear and unwarranted hatred.

Another way in which our psychological circuitry lags behind the conditions of our times can be found in women’s intensity of fear about being raped and murdered by a stranger. In fact, the majority of rapes are committed by men whom women know, and very few actually end in murder. Meanwhile, women tend to underestimate the danger they face from men who are familiar, because that danger has increased over time as our social patterns evolved and more and more women live far away from the protective shield of their families.

Women who do live close to their kin experience dramatically less violence at the hands of husbands than women whose families live hundreds or thousands of miles away.¹² It is likely that the rate at which women are murdered by their mates each year in the modern world is higher than it ever was in ancestral environments. The threat of blood revenge for a daughter or sister who was killed by a jealous mate would have raised the cost of wife killing in the past and deterred many murdering men. Many modern women lack that protective cushion.

The fact that our minds have not caught up with the new mandates of our modern conditions accounts for the disturbingly high number of murders that are still perpetrated every year, despite all of the modern deterrents we’ve developed. We have strong laws, ever more professional police, highly sophisticated forensic investigation methods, and formidable prisons. These deterrents do work, and quite well. Indeed, the most frequently cited reason in our research for not carrying through on a homicidal thought was the fear of getting caught and spending life behind bars. When we asked people to estimate the probability that they would carry out their homicidal fantasies if they could get away with them undiscovered, most men thought that the likelihood would quadruple. Many of us owe our lives to the fact that murder is so costly to commit in the modern world.

Although modern society, with its police and prisons, makes killing more costly than it would ever have been in the past, we still must face the troubling question: are all forms of murder truly maladaptive today in the evolutionary currency of reproductive fitness? I don’t pretend to know all the answers, but they are not as clear as they may appear. Perhaps in some cases the answer seems obvious. The police know that when women are killed the odds are better than fifty-fifty that a jealous husband or jilted boyfriend did it, and the killer risks spending life in a cage. The police should know, if they don’t already, that when a young stepchild suddenly dies the odds are high that a stepparent delivered the lethal blow.

In other cases, the answer is not as apparent, and may be quite disturbing. What about the seventeen-year-old single girl who abandons her infant, delaying reproduction to a more auspicious time? What about the inner-city youth who murders to join a gang, thereby raising his local status, attracting women, reaping money by selling drugs, and funneling resources to his close kin? What about the woman who suffers years of abuse at the hands of her husband, and sees killing as her only way to get herself and her children to safety? Although it’s a disturbing thought, could these forms of murder still be evolutionarily advantageous today?

Furthermore, our deep psychology of homicide-prevention defenses may remain disturbingly functional in the modern world. Consider the man who threatens his wife: If you ever leave me, I will track you down to the farthest corner of the earth and kill you. How many women today stay in unwanted relationships because they fear for their lives? How many death threats, exploiting the evolved staying-alive strategies we all possess, still work in achieving their evolutionary ends?

It would be comforting if we could convince ourselves that all of the evolved mental mechanisms that motivate murder are no longer adaptive in the modern world. It’s just not evident that they aren’t.

MANAGING THE MURDERING MIND

Does the fact that our minds contain adaptations that motivate us to kill mean, in any way, that we should accept this as our nature and give up trying to combat murder? Clearly not. After all, although humans have adaptations for killing, we also have adaptations for cooperation, altruism, peacemaking, friendship, alliance building, and self-sacrifice.¹³ When it comes to murder, human nature is the problem, but human nature also holds the keys to the solution.¹⁴

When I was invited to present my theory of homicide adaptations to the professors at the University of Virginia School of Law, it generated a spirited debate. Some worried that, if it is true that humans have evolved adaptations to kill, then this scientific information might be misused by defense lawyers: “My client couldn’t help killing, Your Honor, his evolved murder mechanisms made him do it.” I would be horrified if the science of murder were abused in this way. Attempts of this sort may be inevitable, but that doesn’t mean they will be effective. Defense lawyers historically have attempted to justify their client’s crimes by any means available—the abuse excuse, the Twinkie defense, television violence, poverty, racism, discrimination, father absence, self-defense, amnesia, drug hazes, hallucinations, and temporary insanity. Some lawyers may well attempt to add “evolved homicidal circuits” to this litany of justifications and excuses, but as I said before, the naturalistic fallacy they would be falling into has been soundly debunked, and our legal system should refute this line of argumentation powerfully.

Another set of law professors at the University of Virginia School of Law offered a legal perspective that I found fascinating, and that may show real promise in deterring murder. Since the goal of the criminal-justice system is to prevent murder, they argued, perhaps we should impose the heaviest sentences for precisely those circumstances in which murder comes most naturally. These evolutionarily novel costs might then help tip the scale in the cost-benefit calculations of would-be murderers, convincing more of them that the costs would be too high.

The theory and evidence presented in this book provides a roadmap of the circumstances—the particulars of the adaptive problems for which murder is one evolved solution—in which people are most likely to contemplate murder. By making murder more costly to carry out in these situations, perhaps the law would be able to increase the benefits of choosing and using nonlethal solutions to each of the relevant adaptive problems.

A deeper understanding of our motivations to kill, and how ingrained they are in our minds, allows us to become better educated about the circumstances in which our lives really are in the gravest danger. Women should be more aware that the most dramatic risk of being killed by a romantic partner occurs when they have irrevocably dumped him, specifically within the first six months after the breakup. They should be highly alert if an ex-mate begins stalking, because they may well be in great danger. Those who are forming stepfamilies should be more attentive to the tensions that can develop in the relationships between stepparents and their stepchildren. The better informed we are about the precise conditions in which the murderous mind is likely to be engaged, the better equipped we will be to avoid activating it and to defend ourselves.

I HAVE SPENT the past seven years of my life studying murder. I found that this work changed me in profound and unexpected ways. You might think that, after spending years poring over five thousand detailed descriptions of homicidal fantasies and the grisly particulars of 375 murders in Michigan, one would grow callous or desensitized to the brutality of murder. I found precisely the opposite. I became increasingly disturbed by it. At one point, while studying the details of a case in which a man murdered his girlfriend, I turned the page and found three color photographs—the dead woman, stripped naked, with bloody knife wounds all around her upper torso. It nauseated me so much that I contemplated abandoning the entire project. To this day I remain haunted by those images.

Another moment of crisis came when I was asked to testify as an expert witness for the defense in a murder trial in Michigan. It was a case about Anne P.,* a twenty-six-year-old woman, who had dated Peter K.* for three months before breaking up with him. At first, Peter’s persistence in trying to win her back seemed harmless, but before long, he began to stalk her. He followed her to work. He tracked where she went in her spare time. He had his friends monitor her whereabouts. He watched her house. Then the phone calls started.

His fury at being dumped had increased when he discovered that she had been seeing someone else; Peter suspected that Anne had started dating another man while they were still together. He began to threaten her, and she became frightened. As the intimidation escalated, Anne’s anxiety drove her to tape-record their conversations, which she turned over to the police. I listened to an agonizing six hours of them.

The conversations revealed a complex web of emotions from both Peter and Anne. Peter berated Anne for seeing another man, telling her that she had betrayed his trust and that he felt thoroughly humiliated. He did not threaten her directly with physical harm, but implied threats many times by talking about his martial arts training, telling her that he could do anything he wanted to her, and saying that no one could stop him. He apologized to Anne when she expressed fear, but did nothing to allay her anxiety. He lapsed into fond reminiscences about the wonderful times they had together and how great the sex had been. But then he told her how much hate and bitterness he had inside.

Anne tried desperately to back him off. She insisted that she was not seeing another man. She told him of the terror she felt about going close to her windows. She swore that she did not mean to hurt him. She lashed out in anger at him for stalking her. She pleaded with him to leave her alone.

Abruptly, Peter’s harassing phone calls and stalking stopped. Gradually, over the next few weeks, Anne started to feel safe, escaping the lonely psychological prison that had terrified her for the past four months. Then, a month after the phone calls stopped, Anne returned home from the grocery store with a male friend. As she got out of her car, Peter pulled up, took aim, and shot them both dead with a .22-caliber handgun. Anne had filed six harassment complaints with the police, but they did not save her life.

While I sat listening to the anguish and terror in Anne’s voice over hours of recorded phone calls, I was at first primarily fascinated by the range of defensive tactics she employed. I sensed her franticness as she pled with Peter to let her go. She tried being nice, almost maternal in her maneuvers; she shifted to being abrupt and rude to back him off; she pretended that his threats were no big deal; she tapped her anger and made threats of her own; she sounded panicky and weak and begged him to stop; and, sadly, toward the end, she sounded exhausted and resigned. Then it struck me. I was listening to the pleading voice of a woman who was murdered in her prime. I was hearing the desperate last gasps of a woman who was now dead forever.

Again I almost closed down my research. But I could not bring myself to terminate a seven-year quest for the meaning behind murder. I did refuse to testify for the defense. Peter is now serving a life sentence without the possibility of parole for killing two innocent people in cold blood, and I’m glad he’s no longer mingling among us.

Poring over the thousands of homicidal fantasies changed me in another unanticipated way. I found myself developing a deep empathy for all who have been fired from their jobs, beaten up by their rivals, humiliated by their peers, abused by their lovers, betrayed by their partners, encroached upon by interlopers, and dumped unceremoniously by the loves of their lives. I could feel their anguish and psychological torment more powerfully. And I found myself feeling a strange and unforeseen sympathy for why they contemplated murder as a means to stop their suffering.

MURDER GIVES US an X-ray of the inner core of human nature. It lays bare the things that matter most to humans everywhere—the necessities of survival, the attainment of status, the defense of honor, the acquisition of desirable partners, the loyalty of our lovers, the bonding of our allies, the vanquishing of our enemies, the protection of our children, and the successes of the carriers of our genetic cargo. These are the things that we humans and our astonishingly victorious ancestors have always been willing to kill and die for.

There are no simple panaceas for the problem of murder. Killing has been a marvelously effective solution to an astonishing array of human social conflicts. The circumstances that trip our homicidal circuits may present too many sprawling fronts to combat successfully. If there is, therefore, one last take-home message in this book, it is that you should listen to your life-preserving intuitions, the ancestral wisdom we all carry within us.

Be aware of just how real the threat of murder is, especially by those we know and those we love. Beware of the man whose uninvited sexual stare lingers a second too long. Exercise caution around a stepparent who just might prefer that you didn’t exist. Take heed of the rival who sits silently seething at your success. Think twice about the stoic whom you have just humiliated in front of his peers. Watch out for the ex-mate of the lover you’ve just lured away. Be wary of the romantics who thought you were “the one” before you unexpectedly spurned them. Be vigilant of the mate turned stalker who just won’t let go. Murderers are waiting, they are watching, they are all around us.