The Anatomy of Violence

by Adrian Raine

  Mundurucú women are clearly attracted to men around them who kill. Have you ever wondered why seemingly sensible, peaceful women want to marry serial killers in prison? Their primitive heartstrings are being plucked by the siren’s call of the serial-killer status. They yearn to be with a strong male, even when their modern minds might logically object. At a milder level we have a morbid fascination with true crime. Something attracts us to violence. That evolutionary pull may even have explained why you bought this book.

  Part of the attraction we have to violence is that when executed in the right place and the right time, it’s adaptive—even today. The vestiges of our evolutionary backgrounds persist, far more than we care to imagine. Let’s take this a step further into the here and the now to examine in what specific situations aggression is adaptive, and what aspects of crime can be explained from an evolutionary perspective.

  KILLING YOUR KIDS

  I mentioned earlier that people in general are a hundred times more likely to be killed on the day they are born than on any other day.19 Murders of children and adolescents are most likely to occur in the first year of life.20 And within that year, eighteen times more children are murdered on the day they were born than on any other day.21 In 95 percent of these cases, the babies were not born in a hospital. They are mostly the product of undesired, unplanned pregnancies. They are battered to death (32.9 percent), physically assaulted (28.1 percent), drowned (4.3 percent), burned (2.3 percent), stabbed (2.1 percent), or shot (3.0 percent).22 It all flies in the face of the exhilaration that most couples experience on the day of their child’s birth. But an explanation for this seeming contradiction can be found within the layers of evolutionary psychology theory.

  Indeed, once we step across the threshold of the home, there are facts that seem to fly in the face of an evolutionary perspective on violence. For example, people are more likely to be killed in their home by a family member than by a stranger. How can that make sense from an evolutionary standpoint? Don’t we expect solid protection of everyone at home to ensure that the family’s genes are passed on to future generations? Martin Daly and Margo Wilson are two Canadian evolutionary psychologists who have done more than anyone else to resolve enigmas like this and to further demonstrate the power of an evolutionary psychological perspective on violence.

  What they demonstrated was an inverse relationship between the degree of genetic relatedness and being a victim of homicide. So the less genetically related two individuals are, the more likely it is that a homicide will take place. For example, in Miami, 10 percent of all homicides were the killings of a spouse—a family killing—but of course, spouses are almost always genetically unrelated. In fact, Daly and Wilson found that the offender and the victim are genetically related in only 1.8 percent of all homicides of all forms.23 So 98 percent of all homicides are killings of people who do not share their killer’s genes.

  Selfish genes in their strivings for immortality wish to increase—not decrease—their representation in the next gene pool. Hence this inverse relationship between genetic relatedness and homicide. On the other hand, if you are living with someone not genetically related to you, you are eleven times more likely to be killed by that unrelated person than by someone genetically related to you.

  Stepparents are a particularly pernicious case in hand, a fact captured in countless myths and fairy tales. Remember the grim story of Hansel and Gretel, whose wicked stepmother badgered their natural father into leaving his children deep in the woods to die of starvation? Or Sleeping Beauty’s evil and vain stepmother, who ordered a hunter to take her into the woods and slaughter her? Recall Cinderella’s cruel stepmother? Actually, the reality is so potent that our childhood lives are full of images of mean stepmothers—real or imaginary—almost as an eerie warning call for us to be on our guard.

  Did you grow up as a child with a stepparent? If you did and you survived unscathed, you’ve done pretty well. In England, only 1 percent of babies live with a stepparent,24 and yet 53 percent of all baby killings are perpetrated by a stepparent.25 Data from the United States show a similar pattern—a child is a hundred times more likely to be killed as a result of abuse by a stepparent than by a genetically related parent. If we look at child abuse, we see the same thing. Stepparents are six times more likely to abuse their genetically unrelated child under the age of two than genetic parents.

  It’s a finding that makes you wonder if in cases of death from abuse by someone thought to be the biological parent, that person may not be the genetic parent after all. In cases where the children and the father believe that they are genetically related, it is estimated that in about 10 percent of cases the father is not the genetic father. Could at some subconscious, evolutionary level the father sense genetic unrelatedness and pick on the unrelated child? Such abuse would be a paternal strategy to push that child out, to minimize the resources given to him, and instead maximize resources for other, genetically related children. We know that stepparents sometimes selectively abuse their stepchildren, sparing the children in the family who are genetically related to them.26

  Such actions of some stepparents can thus be comprehensible from an evolutionary perspective. But more perplexing are parents who kill children they are genetically related to. How can evolutionary theory come to grips with these killings?

  The basic concept to remember here, if you think back to your own parents when you were growing up, is that they likely worked hard to raise you—and don’t they just let you know it sometimes! They worked their fingers to the bone and sacrificed much for your future betterment. Okay, so that’s par for the course when it comes to looking after your own genes. But also bear in mind that the longer a child lives, the more her parents invest in her. But suppose someone’s genetic parents change their minds about their investment? If they do, they ought to do it early on before they waste more energy. And that’s exactly what we see.

  Take a look at the top graph in Figure 1.2, showing the age at which a child will be killed by its mother if she is indeed going to kill it. It shows homicides per million children per year averaged over a period from 1974 to 1983 in Canada. You’ll see that the peak age for killing is in the very first few months of that little baby’s life.27 After that time, the homicide rate drops dramatically and keeps on declining right throughout adolescence. Soon after birth the mother bails out on her own baby. Maybe she wants to move on. Maybe her mate has moved out and she knows she’s better off without this baggage, better able to attract a new mate. Whatever the reason, there is a strong age effect to be explained.

  Figure 1.2 Age at which Canadian children are murdered by their mother, father, and others

  I think I know what you’re thinking. Some mothers just after birth have puerperal psychosis. They sink into a very deep depression with psychotic features, and amid their despair and madness they may kill their kid. Fair point, because this condition does affect about one in a thousand mothers after birth. But the response lies in data shown in the middle graph of Figure 1.2. You can see exactly the same infanticide age curve for fathers.28 If they are going to kill, it’s again in the very first year of life, when their investment is minimal. Fathers don’t give birth and so they don’t suffer from puerperal psychosis. Consequently, this form of psychosis cannot explain the maternal data in Figure 1.2.

  Maybe it’s all that screaming and sleeplessness that comes in the first year that drives the parents to kill their offspring. It’s not a bad explanation. But tell me, if you have ever had a child, what was the worst year—that first year when they were innocently crying, or the teenage years, when they were yelling in your face? Or, if you haven’t had kids, at what age do you think you were hardest on your mother and father? I’d go for the teenage years any day, and yet look at the rate at which parents kill their teenagers—that’s strangely when children are least likely to get killed by them. But if you are a teenager don’t push your luck with your parents, as a few do get killed.

  Don’
t push your luck with anyone else either. You’ll see from the bottom chart in Figure 1.2 that when we look at the killings of kids by nonparents, rates are low early on but shoot up in the teenage years. Why? Because that’s the age when renegade youths are cruising the streets looking for fun and meeting up with strangers. It’s also when children are less closely supervised by their parents and when risk-taking is highest.

  There are other environmental triggers that from an evolutionary perspective help explain why parents might kill their young offspring. A baby may be born with a congenital abnormality that reduces the odds of survival or reproduction, or it may have a chronic illness that saps parental resources. Even with normal offspring, if food is short it may pay the parents in terms of genetic investment to spend scarce resources on the survival of an older sibling closer to the age of maturity and independence, rather than spreading the butter too thinly, trying to support both the newborn and the older sib.

  Even if there is no older sibling, killing the baby could make evolutionary sense. In some bird species where both parents forage for their offspring, the death of one parent can result in the other parent abandoning the offspring. The load is just too hard to bear, and it’s better for the remaining parent to look after number one and try again in the reproductive success game. Don’t we sometimes get a sense of that in stories of young mothers abandoning their babies? We tend to interpret their actions as due to social processes like immaturity, shame, or teenage impulsivity. Shame may be the superficial explanation, but at a deeper level the underlying cause may be cold-blooded maximization of reproductive success. The negative emotions and behaviors that we attribute to the mother in trying to explain the homicide may not be the whole story. The selfish genes inside the teenage killer mom may be the ultimate source of such callous, cold-blooded behavior.

  Figure 1.3 Age of mother when she kills her own child

  There’s one more point to make about parents killing their children: how old the mother is when she kills her own child. The upper graph of Figure 1.3 shows the rate of child homicides as a function of the mother’s age among the Ayoreo Indians of South America. It’s highest when the mother is under the age of twenty, and it goes down after that. Why would that be? The mother is more fertile when she’s younger—and more attractive in drawing a desirable mate to her. The older she is, the more it makes sense to hold on to her long-term genetic investment because it’s harder to make up the loss at this later point in her reproductive life.

  And it’s not just the Ayoreo Indian mothers who kill at an early age. If you look at Canadians in the lower half of Figure 1.3, you’ll see the same age-to-murder curve.29 Your mother is much more likely to kill you when she is still young. Being young, her reproductive years lie ahead of her and she has more options. Perhaps the current biological father has abandoned her. Perhaps she has a new suitor who can promise her more. Either way, the selfish gene ticking away inside her signals that it’s time to dump her baggage and go on vacation looking for a new mate.

  Put all of this together, and what comes across is that genetic relatedness, fitness, and parental investment are intriguing reasons for why adults kill their kids. Patterns of homicide can indeed be clarified by the application of sociobiological principles. Of course there are other processes that help explain why a parent kills his or her child—it’s not just the selfish gene at work. Yet whether we are aware of it or not in the twenty-first century, the machinations of deep evolutionary forces are laboring away down in the depths of our humanity, forging devious tools to maximize our genetic potential. And behind those closed doors in the family home, those forces don’t end with killing your kids.

  RAPING YOUR WIFE

  Is rape an act of hate? A malicious and derisory act against women condoned by a patriarchal society where men attempt to control and regulate their womenfolk? Or can this act of violence be partly explained by evolutionary psychology?

  We can view the rape of a nonrelative as the ultimate genetic cheating strategy. Rather than striving to accrue resources to attract a female and investing years in the upbringing of their offspring, a male can cut through this tedious process in the twinkling of an eye. He just needs to rape a woman. Men have hundreds of millions of sperm that are always at the ready to inseminate a woman. The sex act is quick. And the male can immediately walk away, never to see that woman again. He knows that if pregnancy does occur, there is a decent chance that the female will care for their joint progeny. His selfish genes have reproduced.

  How often will a rape result in a pregnancy? This was estimated in one study of 405 women aged twelve to forty-five who had suffered penile-vaginal rape. The total base rate was 6.42 percent, which was twice as high as the 3.1 percent base rate for unprotected penile-vaginal intercourse in consensual couples. After correction for the use of contraceptives, the pregnancy base rate from rapes was estimated at 7.98 percent.30 The rates of pregnancies from rape can only be estimates because paternity is not investigated with definitive DNA evidence. Some women could “invent” a rape as a cover-up for an unwanted pregnancy. However, other studies have also reported higher rape-pregnancy rates than consensual-sex-pregnancy rates. It is nevertheless surprising. If we accept the findings, why would rape be more likely to result in a pregnancy?

  One conceivable hypothesis is that rapists are more likely to inseminate fertile women. Rapists select their victims, and we certainly know that they are far more likely to select women at their peak reproductive age than other women.31 Furthermore, putting age aside, the possibility that a rapist may be more visibly drawn to women who are the most fertile is not impossible. Females with a smaller waist relative to their hips are viewed as more attractive in many cultures throughout the world. This smaller waist-to-hip ratio is also associated with increased fertility as well as better health.32 Consequently, male rapists could in theory select a more fertile female, consciously or subconsciously, based on how she looks.

  Not all rapists choose victims they find attractive. It can even be the other way around. When I worked with prisoners in England, one rapist told me that he specifically picked out unattractive women to rape. Why would he do this? His argument was that an unattractive woman does not get enough sex, so it’s okay to give her the sex that she really wants. This is just one example of a number of cognitive distortions that some rapists have.33 Their perverted belief is that women actually enjoy the act of rape and interpret it as the experience of a lifetime—their ultimate sexual fantasy coming true.

  Ideas like this may be inadvertently fueled by the fact that some women when raped actually achieve orgasm, even though they may strongly resist and are traumatized by the attack.34 True prevalence data are hard to come by because rape victims understandably are embarrassed to admit that they achieved orgasm during such a disgraceful violation. Clinical reports place the rate of the victim experiencing orgasm at about 5 to 6 percent, but clinicians also report that they suspect the true rate to be higher. This may well be the case, because research reports document that physiological arousal and lubrication occurs in 21 percent of all cases. Why would that happen? Because in half the cases, the date-raped woman was actually attracted to the perpetrator before the act. Orgasm and the associated contractions are thought to facilitate conception by contracting the cervix and rhythmically dipping it into the sperm pool. This admittedly has a modest effect, as sperm retention is increased by only approximately 5 percent with orgasm.

  Clearly, conception does not require orgasm,35 so we cannot place too much weight on the physiological arousal of some women during rape as a prelude to pregnancy. Nevertheless, the fact remains that rapists generally select their victims and appear to consciously or subconsciously select more fertile women. This selection strategy would explain the purported increased pregnancy rate in rape victims and can be viewed in an evolutionary context. If a man is going to take risks raping a woman, the strategy would be to pick the fertile one and enhance one’s inclusive fitness.

>   There are, of course, risks associated with this particular cheating strategy. The male could suffer physical injury. Worse, he could be detected and beaten. Throughout much of human history rapists have been alienated or killed. In modern times he would be thrown into prison alongside psychopaths and murderers, where as a sex offender he is at high risk for being beaten and raped himself. So evolutionary theory argues that there is a subconscious cost-benefit analysis at work—weighing the potential costs resulting from detection against the benefits of producing a child. Dominant men with resources can already attract mates, so one might expect that the cost-benefit analysis might tip the scales in favor of rape when the perpetrator has relatively fewer resources. In support of this prediction, rapists are indeed more likely than non-rapists to have lower socioeconomic status, to leave school at an earlier age, and to have unstable job histories in unskilled occupations.36

  We can question evolutionary theory because it can be too all-encompassing; we cannot take it too far in explaining violence. Drug cartels in Colombia and the availability of handguns in the United States contribute significantly to explaining why these countries today have high homicide rates, and yet these influences lie outside the domain of evolutionary theory. I think you would admit that an evolutionary perspective can help explain facts about rape in quite a compelling way. While women of any age can be raped, we’ve noted that men are much more likely to rape women of reproductive age.37 Interestingly, women of reproductive age who are raped experience more extreme psychological pain than younger or older women. This has been interpreted as an evolutionary learning mechanism that focuses these women’s attention on avoiding contexts where they could be raped and have their overall reproductive success reduced.38 At another level, we know that men find it far easier than women to have sex without concomitant emotional involvement. Why? Because they do not need to hang around after the sex act is over. In contrast, from an evolutionary perspective, women need a long-term commitment from their male mate to help rear any child that might result from their union, and so they have more need of an emotional, personal relationship. Finally, men very rarely kill the women they rape; although they have the potential to kill, they want their offspring to survive.