by David Buss
| Homicide Mechanisms | The Murderer Next Door | Brain | Adaptations |
Theories that invoke local cultural norms cannot satisfactorily explain a universal human pattern. - Amazon
Actual homicides are statistically rare and thus difficult to study. For every homicide that is actually committed, however, there may be dozens or hundreds of thoughts or fantasies that individuals entertain about killing. Consider this homicidal fantasy reported by a male undergraduate:
I wanted to kill my old girlfriend. She lives in another city and I was just wondering if I could get away with it. I thought about the price of airfare and how I might set up an alibi. I also thought about how I would kill her in order to make it look like a robbery. I actually thought about it for about a week and never did come up with anything. (Kenrick, D. T., & Sheets, V. (1993). Homicidal fantasies. Ethology and Sociobiology, 14, 231–246)
This man did not kill his girlfriend. But the recurrence of thoughts about homicide opens up a window for investigation into the psychology of homicide.
Evolutionary psychologists Doug Kenrick and Virgil Sheets have capitalized on this opportunity, conducting two studies on a total of 760 undergraduates. Their methods were simple: They asked subjects to provide demographic information, including their age and sex, and then describe the last time they had thoughts about killing someone. They inquired about the circumstances that triggered the violent thoughts as well as the content of those thoughts: “who you wanted to kill, how you imagined doing it, etc.” (Kenrick & Sheets, 1993, p. 6). They queried subjects about the frequency of fantasies, the specific relationship with the person they thought of killing, and whether the fantasy had been triggered by a physical attack, a public humiliation, or any on a list of other provocations.
First, more men (79 percent) than women (58 percent) reported experiencing at least one homicidal fantasy. Second, 38 percent of the men but only 18 percent of the women reported having had several homicidal fantasies. Third, men’s fantasies tended to last longer than women’s fantasies. Most women (61 percent) reported that their homicidal thoughts typically lasted only a few seconds. Most men reported that their homicidal thoughts lasted a few minutes, with 18 percent reporting that their fantasies lasted a few hours or longer. These findings support the hypothesis that men are psychologically more disposed to homicide than women—a finding that is also supported by the actual homicide statistics.
Sex differences were also apparent in the triggers of homicidal thoughts. Men were more likely than women to have homicidal thoughts in response to a personal threat (71 percent versus 52 percent), the fact that someone stole something from them (57 percent versus 42 percent), a conflict over money (27 percent versus 10 percent), and public humiliation (59 percent versus 45 percent).
Inclusive fitness theory predicts greater conflicts between children and their stepparents than between children and their genetic parents, and the homicidal fantasy evidence bears this out. Of those who lived with a stepparent, fully 44 percent reported fantasies about killing them. Among those who lived for longer than 6 years with a stepparent, 59 percent reported such homicidal fantasies. In contrast, the figures for killing a mother or a father were lower: 31 and 25 percent, respectively.
How can these findings be explained from an evolutionary perspective? There
are two distinct possibilities. The one adopted by Kenrick and Sheets (1993)
and by Daly and Wilson (1988) may be called the “
males have evolved a psychological propensity for violence as a means of coercive control and eliminating sources of conflict. This propensity typically results in threats of violence or sublethal violence as a behavioral output. Occasionally, however, there is a “slip,” such that the violence accidentally bubbles over into a homicide: “There is brinkmanship in any such contest, and the homicides by spouses of either sex may be considered slips in this dangerous game” (Daly & Wilson, 1988). The same slips may occur in other forms of homicide, such as male–male homicide.
An alternative is “
humans have evolved specific psychological mechanisms that predispose them to kill others under certain predictable circumstances such as warfare, intrasexual rivalry, or spousal infidelity or defection.
Humans have homicidal fantasies as one component of these evolved homicide mechanisms. These fantasies allow a person to build and work through the homicidal thoughts. They allow a person to evaluate the costs and benefits of various courses of action. And they lead a person to kill when the perceived benefits outweigh the perceived costs and to inhibit killing when someone perceives that costs are too high (or when less costly solutions to the problem are available). In most circumstances, the costs are too great:
In all societies, the person risks the wrath of kin and punishment from other interested members of the group (Daly & Wilson, 1988). These perceived costs deter many from killing.
The proposal is not that men have a “killer instinct” whereby they are impelled to kill regardless of circumstances. Rather, it is that
acts of killing are one form of behavioral output of evolved homicide adaptations whose activation is triggered by particular forms of input, followed by evaluation of costs and benefits.
According to homicide adaptation theory,
a number of homicide adaptations have evolved as;
-context-sensitive solutions to an array of adaptive problems -
These include
- protecting oneself and kin from injury or death,
- gaining access to scarce resources needed to survive and reproduce,
- eliminating rivals,
- removing key competitors of one’s own children, and
- depriving rivals of access to valuable mates (Duntley & Buss, 2011).
Because getting killed inflicts dramatic costs on victims, however, selection has fashioned co-evolved anti-homicide defenses that function to prevent getting killed and to inflict costs on those who attempt to kill. The co-evolution of homicide adaptations and anti-homicide defenses results in offenses, defenses, tactics to counter the defenses, and tactics to counter the counters to the defenses, producing a perpetual coevolutionary arms race.
Many lines of evidence support the plausibility of homicide adaptation theory. First, the comparative evidence strongly suggests adaptations exist for killing conspecifics in many species, including chimpanzees, our closest primate relative (Wrangham, 2004). Second, the paleontological evidence—ancient bones and stones—reveals a long history of human homicide going back tens of thousands of years (Larsen, 1997). Third, the cross-cultural evidence reveals that intrasexual rivalry homicides, infanticides, and warfare are universal phenomena, even in cultures previously believed to be peaceful such as the !Kung San of Africa (Ghiglieri, 1999; Keeley, 1996). Fourth, the archeological record reveals weapons such as maces, lances, tomahawks, and swords; ancient art depicting murders; and defensive structures such as moats filled with water lined with spikes on the bottom, fortresses, palisades, and other structures designed to ward off homicidal attackers. Fifth, a compilation of 11 anthropological studies reveals that roughly 30 percent of all adult deaths were caused by violence, with the majority of victims being male (Walker & Bailey, 2013). Sixth, the murder of genetic relatives is extremely rare, as predicted by inclusive fitness theory, except when those genetic relatives interfere with more successful avenues for achieving reproductive success (McCullough, Heath, & Fields, 2006). And seventh, psychological evidence reveals specialized cognitive and emotional circuits that seem well designed for killing in particular circumstances (Duntley & Buss, 2011).
Figure 10.4 Likelihood of Killing the Rival If the Crime Were Not
Discovered
Source: Buss, D. M., & Duntley, J. (1998). Evolved homicide modules.
Paper presented to the Annual Meeting of the Human Behavior and Evolution
Society, Davis, California, July 10.
Consider as one example the circumstances that trigger homicidal thoughts, the possible targets of killing, and sex differences in how close people say they have come to killing (see Figure 10.4). Intrasexual rivals compose the largest category of homicidal ideation. Among intrasexual rivals, the most powerful triggers for men occur when a rival has sex with their mate, humiliates them in public, beats them up, or steals their money—costs that inflict some of the most severe adaptive problems on men. And men indicate a far greater likelihood than do women of coming close to killing in these circumstances, indicating a close correspondence between psychological design for murder and the circumstances in which men actually do murder.
These competing evolutionary hypotheses—the slip-up hypothesis and homicide adaptation theory—have not yet been pitted against each other directly in empirical tests. The high prevalence of homicidal fantasies, the predictability of the circumstances that trigger them, the evidence of sex differences, the large fitness consequences of killing and being killed, the high prevalence of homicide in traditional hunter-gatherer societies, and the premeditated quality of many homicides, however, do not accord well with the slip-up hypothesis. Within the next decade, we can expect a resolution to the scientific debate about whether humans have evolved specific homicide adaptations.
Summary (of the entire chapter the above section is within)
From the perspective of evolutionary psychology, aggression is not a singular or a unitary phenomenon. Rather, it represents a collection of strategies that are manifested under highly specific contextual conditions. The mechanisms underlying aggression have emerged, in this view, as solutions, albeit sometimes repugnant ones, to distinct adaptive problems such as resource procurement, intrasexual competition, hierarchy negotiation, and mate retention.
From this perspective, we expect variability in aggression—between the sexes, among individuals, over the life span, and across cultures. It illustrates the point that variability does not imply that our evolved biology is irrelevant. An evolutionary psychological perspective is truly interactionist: It specifies a set of causal conditions that our evolved psychology is designed to be sensitive and responsive to, such as particular features of the perpetrator, victim, social context, relative physical formidability, coalitional strength, and so on.
An evolutionary perspective suggests at least six classes of benefits that would have accrued to ancestors who used an aggressive strategy: co-opting the resources of others, defending oneself and one’s kin against attack, inflicting costs on intrasexual rivals, negotiating status and power hierarchies, deterring rivals from future aggression, and deterring long-term mates from infidelity or defection.
Sound evolutionary arguments predict that aggression is likely to emerge more strongly among men, with both aggressors and victims being men. Given a mating system of some degree of polygyny, sexual selection will favor risky tactics among men both to gain sexual access to more women and to avoid being excluded from mating entirely. Empirically, most physical aggression is perpetrated by men and most of the victims are men. This evidence includes same-sex homicides across cultures, the frequency of bullying in school, and ethnographic evidence of physical violence from Australian aboriginal communities.
Many contexts are linked with aggression occurring within each sex-of-perpetrator by sex-of-victim combination. Contexts triggering men’s aggression against other men include being unemployed and unmarried—circumstances that suggest that men are on a path to being excluded from mating, which may activate a risky aggressive strategy. Men also aggress against other men when their status and reputation are threatened and when they observe or suspect a rival of sexually “poaching” their mate.
Women aggress against other women primarily in the context of competition over attracting or retaining mates, over friendship violations, and sometimes over food. Women, however, are far less likely to use physical aggression, preferring instead to derogate their competitors verbally or to socially ostracize them. Two prominent derogation tactics are calling their rivals promiscuous and impugning their rival’s physical appearance—both of which attain their effectiveness because they violate men’s desires in a long-term mate.
Men aggress against women mainly to control their sexuality. Sexual jealousy is a key context triggering men’s aggression against their mates. Presumably aggression historically functioned to deter a mate from further infidelity or from leaving the relationship entirely. Younger women are more vulnerable to aggression from their partners, presumably because they have higher reproductive value, and hence ancestral men had a greater incentive to maintain exclusive sexual access to them.
Women kill men rarely, but when they do, it is typically in self-defense. The context usually involves a woman defending herself against a mate who is enraged about a real or suspected infidelity or when the woman is breaking up with the man.
Warfare, defined as aggression by a cooperative coalition against another cooperative coalition, is extraordinarily rare in the animal world. Only two mammalian species have been observed to engage in coalitional aggression: chimpanzees and humans. An evolutionary perspective predicts that warfare will be practiced primarily by men, with the primary reproductive benefit being increased sexual access to women. Empirical evidence supports this theory: Men have engaged in warfare throughout human recorded history; sexual access to women appears to be a recurrent benefit that flows to victors of warfare; men more than women spontaneously assess their fighting ability relative to others; and men more than women value coalition members who are strong, are brave in the face of danger, and have good fighting abilities. Men display other phenomena that suggest evolved warfare adaptations, such as unusually high mortality rates in traditional cultures; a greater proclivity to attack other countries in simulated war games; and a greater tendency to display strong ingroup/outgroup distinctions and to derogate outgroup members as being subhuman. Although more research is needed, the available evidence supports the evolutionary theory of warfare and suggests specific psychological mechanisms designed to wage war.
The final section of the chapter considered two contrasting hypotheses designed to explain the evolution of the killing of other human beings. The first hypothesis suggests that killings are “slip-ups” or by-products that result from the use of violence and the threat of violence as a means of coercively controlling others. The second hypothesis suggests that humans, especially men, have evolved specific homicide adaptations that are designed to motivate killing other humans under specific circumstances when the benefits outweigh the costs. The high prevalence of homicidal fantasies, the predictability of the circumstances that trigger them, the evidence of gender differences, and the premeditated quality of many homicides all seem to support the homicide adaptation theory, although further research is needed to compare predictions from the two theories directly.
Critical Thinking Questions
In every culture, men are more violently aggressive than women, yet women often use indirect or verbal aggression such as gossip against their rivals. Explain why women have evolved to be more reluctant to engage in a strategy of violent aggression.
More muscular men and more attractive women tend to be more prone to anger than less muscular men and less attractive women. Explain how these findings support the recalibration theory of anger.
In all of human recorded history, there is not a single instance of women banding together with other women to attack and kill another group of women. Yet history is filled with men forming war parties to attack other groups of men. Explain, from an evolutionary perspective, why men but not women would risk their lives to go to war.
Suggested Readings
Buss, D. M. (2005). The murderer next door: Why the mind is designed to kill. New York: Penguin.
Campbell, A. (1999). Staying alive: Evolution, culture, and women’s intrasexual aggression. Behavioral and Brain Sciences, 22, 203–252.
Chagnon, N. (1988). Life histories, blood revenge, and warfare in a tribal population. Science, 239, 985–992.
Daly, M., & Wilson, M. (1994). Evolutionary psychology of male violence. In J. Archer (Ed.), Male violence (pp. 253–288). London: Routledge.
Duntley, J. D., & Shackelford, T. K. (Eds.). (2008). Evolutionary forensic psychology. New York: Oxford University Press.
Gat, A. (2015). Proving communal warfare among hunter-gatherers: The quasi-Rousseauan error. Evolutionary Anthropology: Issues, News, and Reviews, 24 (3), 111–126.
Hill, K., Hurtado, K., & Walker, R. S. (2007). High adult mortality among Hiwi hunter-gatherers: Implications for human evolution. Journal of Human Evolution, 52, 443–454.
Johnson, D. D. P., McDermott, R., Barrett, E. S., Crowden, J., Wrangham, R., Mcintyre, M. H., & Rosen, S. P. (2006). Overconfidence in war games: Experimental evidence on expectations, aggression, gender, and testosterone. Proceedings of the Royal Society B, 273, 2513–2520.
Lindenfors, P., & Tullberg, B. S. (2011). Evolutionary aspects of aggression: The importance of sexual selection. In Advances in genetics (Vol. 75, pp. 7–22). New York: Academic Press.
Navarrete, C. D., Olsson, A., Ho, A. K., Mendes, W. B., Thomsen, L., & Sidanius, J. (2009). Fear extinction to an out-group face. Psychological Science, 20, 155–158.
Raffield, B., Price, N., & Collard, M. (2017). Male-biased operational sex ratios and the Viking phenomenon: an evolutionary anthropological perspective on Late Iron Age Scandinavian raiding. Evolution and Human Behavior, 38 (3), 315–324.
Rucas, S. L., Gurven, M., Winking, J., & Kaplan, H. (2012). Social aggression and resource conflict across the female life-course in the Bolivian Amazon. Aggressive Behavior, 38 (3), 194–207.
Sell, A., Sznycer, D., Cosmides, L., Tooby, J., Krauss, A., Nisu, S.,… & Petersen, M. B. (2017). Physically strong men are more militant: A test across four countries. Evolution and Human Behavior, 38 (3), 334–340.
Shackelford, T. K., & Weekes-Shackelford, V. A. (Eds.). (2012). The Oxford handbook of evolutionary perspectives on violence, homicide, and war. New York: Oxford University Press.
Sugiyama, M. S. (2014). Fitness costs of warfare for women. Human Nature, 25 (4), 476–495.
Van Vugt, M. (2009). Sex differences in intergroup aggression and violence: The male warrior hypothesis. Annals of the New York Academy of Sciences, 1167, 124–134.
Walker, P. L. (2001). A bioarchaeological perspective on the history of violence. Annual Review of Anthropology, 30, 573–596.
Evolutionary Psychology: The New Science of the Mind 6th Ed. by David Buss
https://www.amazon.com/Evolutionary-Psychology-New-Science-Mind/dp/1138088617/
The Murderer Next Door: Why the Mind Is Designed to Kill
-by
David M. Buss
David Buss's pioneering work has made major national news in the past, and this provocative book is sure to generate a storm of attention. The Murderer Next Door is a riveting look into the dark underworld of the human psyche—an astonishing exploration of when and why we kill and what might push any one of us over the edge. A leader in the innovative field of evolutionary psychology, Buss conducted an unprecedented set of studies investigating the underlying motives and circumstances of murders, from the bizarre outlier cases of serial killers to those of the friendly next-door neighbor who one day kills his wife.
Reporting on findings that are often startling and counterintuitive—the younger woman involved in a love triangle is at a high risk of being killed—he puts forth a bold new general theory of homicide, arguing that the human psyche has evolved specialized adaptations whose function is to kill. Taking readers through the surprising twists and turns of the evolutionary logic of murder, he explains exactly when each of us is most at risk, both of being murdered and of becoming a murderer. His findings about the high-risk situations alone will be news making.
Featuring gripping storytelling about specific murder cases—including a never used FBI file of more than 400,000 murders and a highly detailed study of 400 murders conducted by Buss in collaboration with a forensic psychiatrist, and a pioneering investigation of homicidal fantasies in which Buss found that 91 percent of men and 84 percent of women have had at least one such vivid fantasy—The Murderer Next Door will be necessary reading for those who have been fascinated by books on profiling, lovers of true crime and murder mysteries, as well as readers intrigued by the inner workings of the human mind.
https://www.amazon.com/gp/product/0143037056/
Ideas about the parts of the brain required for murder from the 1970s
Homicide Adaptations
Joshua D. Duntley, David M. Buss
Richard Stockton College, University of Texas, Austin, United States.
We propose Homicide Adaptation Theory as a new explanation for why people kill. Multiple homicide mechanisms have evolved as effective context-sensitive solutions to distinct adaptive problems. Killing historically conferred large fitness benefits: preventing premature death, removing cost-inflicting rivals, gaining resources, aborting rivals' prenatal offspring, eliminating stepchildren, and winnowing future competitors of one's children. Homicidal ideation is part of evolved psychological design for killing, functioning to mobilize attention, rehearse scenarios, calculate consequences, and motivate behavior. Because being killed inflicts temporally cascading costs on victims, selection has forged death-prevention strategies, producing co-evolutionary arms races between homicidal strategies and anti-homicide defenses.
© 2011 Elsevier Ltd. All rights reserved.
The murder of an individual or his close kin are among the greatest costs that can be inflicted on any individual. The dead cease to contribute to their own affairs and cannot actively influence the affairs of their families, friends, or enemies. Wherever written laws exist, killing is always singled out as a crime. No other infraction comes attached with greater punishment. Where written laws are absent, killing typically constitutes a major cause of death, sometimes accounting for the mortality of a third of all males (Keeley, 1996). Although cultures with written laws, hired police forces, and the prospect of imprisonment have substantially lower homicide rates than cultures lacking them the lifetime odds of dying by the hand of another in modern societies run as high as one in twenty-six for certain sub-groups, such as inner-city males (Ghiglieri, 1999).
In this paper, we review data on patterns of homicide in the United States and around the world. We introduce our evolutionary theory of homicide and discuss how adaptationist logic can both explain existing findings on homicide and lead to novel predictions. We explore the costs of being a victim of lethal aggression and explain how adaptations that produce homicide and adaptations that defend against being killed are locked in an antagonistic coevolutionary arms race. Finally, we explore evidence supporting Homicide Adaptation Theory...
3. Homicide Adaptation Theory
By advancing Homicide Adaptation Theory, we propose that there have been highly specific and recurrent contexts over human evolutionary history in which the fitness benefits of killing out-weighed the fitness costs. These contexts are defined by distinct adaptive problems for which murder was one effective solution among several potential other, non-lethal solutions. Examples of these adaptive problems include self-defense, kin protection, curtailing the costs of investing in genetically unrelated individuals, curtailing the costs of investing in a genetically related individual with poor survival and reproductive prospects, acquisition of reproductively relevant resources, acquisition of new mates, and the elimination of a cost-inflicting rival. We propose that humans have evolved distinct, context-sensitive psychological mechanisms that determine whether homicide or a non-lethal adaptive solution will be implemented. We propose that these mechanisms are activated by a delimited set of circumstances, and that they are designed to produce the death of conspecifics...
https://labs.la.utexas.edu/buss/
https://labs.la.utexas.edu/buss/files/2015/09/Homicide-Adaptations-Final-Published-Version.pdf
Human nature, mating motives may lead to murder, book theorizes
Killing is fundamentally in our nature, having evolved over thousands of years from intense competition for reproductive success, according to a new theory by Dr. David Buss, an evolutionary psychologist at The University of Texas at Austin.
https://news.utexas.edu/2005/05/23/human-nature-mating-motives-may-lead-to-murder-book-theorizes/
