Computed across a lifespan of 75 years, there is a 1 in 200 chance that an individual in the United States will be murdered. The frequency of homicide and this startlingly high statistic warrant more concerted efforts to research the psychological underpinnings motivating homicide. The history of the study of the psychology of homicide is replete with theoretical shifts—some of which have led to empirical dead ends and others to tremendous advances. Explaining the motivations of a murderer historically has been a difficult task for psychologists because of the wide array of individual, situational, and cultural variables influencing the development of homicidal behavior. Recent psychological research includes both theoretical and methodological advances that have allowed for new, unprecedented insights into the psychology of homicide.
Theoretical Perspectives on Homicide
Several theories have been developed over the brief history of psychology seeking explanations of the patterns of homicide. These theories have followed larger movements within psychology. Movements have proceeded from individualistic explanations of homicide in the late 19th and early 20th centuries to more environmental explanations throughout much of the past century. Modern theories seek to address the limitations of previous theories by accounting for a broader range of causes of human behavior. Rather than discussing all the theories, this entry expands on those that are particularly influential and provides an organizational framework to anchor and interpret the changes in these theories.
George Vold organized various theories of the mid 20th century into spiritistic and naturalistic explanations. To focus on scientific explanations of human behavior, we will not discuss spiritistic accounts of homicide. Naturalistic explanations include those that lend themselves to empirical scrutiny and include hereditary and defectiveness theories, mental deficiency theories, and mental illness theories. Hereditary and defectiveness theories view homicide as the product of biological and genetic causes. Mental deficiency theories argue that homicide is the product of low intelligence. Mental illness theories, espoused first by Sigmund Freud, have been better received than mental deficiency theories. Although Freud’s psychoanalytic theory was a starting point for explaining the psychology behind homicide, psychoanalytic theory is now recognized as empirically barren. Freud’s influence was lasting, however, with many later contributions revealing Freudian pedigree. Evidence of views of homicide as the product of psychopathology is revealed by the first study on homicide, published in 1898 in the psychology journal American Journal of Insanity by Charles Bancroft. Continuing to the present day is the perspective of understanding homicide as the result of pathological psychological manifestations. The theories mentioned so far focus primarily on characteristics internal to an individual that may influence homicidal behavior. There was a focus on more environmental explanations of homicide in the early to mid 20th century, largely in reaction to the previous focus on intra-individual explanations of homicidal behavior.
Environmental Theories of Homicide
Environmental theories can be described generally as focusing on sources or causes of homicidal behavior outside the individual. Examples of such theories include socialization theories, symbolic interactionism, social structural theories, control theory, and social ecology theory. Socialization theories of homicide and aggression have historically been among the most popular and influential accounts of the motivations for homicide. The sex difference in the commission of violent crimes— including homicide—was one of the first and most obvious observations demanding explanation. Men are more often than women both the offenders and the victims of homicides. Socialization theories argue that men, more than women, have been socialized to view aggression as a permissible means to achieve certain ends. This differential socialization for aggressive behavior in men and women, it is argued, can explain the greater homicide rates among men. While this theory has been well received within psychology, there is growing evidence that an exclusive reliance on this theoretical position to explain homicide patterns leads to incomplete conclusions. Socialization theories push back one step many of the most intriguing questions psychologists working to understand homicide have tried to answer. Why are men and women differentially socialized to behave aggressively? Why are boys and girls differentially receptive to certain aspects of environmental input? Socialization theories cannot provide answers to such questions. Despite the limitations of environmental theories, insight has been gained from the research conducted by social scientists focusing on social and cultural influences. One notable finding reflecting the cultural and demographic variables within cultures has resulted from research on homicide rates across the United States.
Social scientists have identified key sociocultural beliefs and attitudes that vary by region and have analyzed homicide rates as a function of these different beliefs and attitudes. The Southern states in the United States adhere more strongly to a “culture of honor” than other regions. In the Southern states, men act more aggressively than men in the Northern states to protect their honor and their reputation. This difference is arguably generated by exposure to a culture in which honor and reputation are very important in protecting resources. Of the state executions that have occurred since 1977, 82% have occurred in the Southern region of the United States. In addition to these social explanations of homicide, recent breakthroughs have been made in understanding the biological roots of homicide.
Biological Theories of Homicide
Advances in technology now provide researchers with an unprecedented window into the brain activity of murderers. These technological advancements include functional magnetic resonance imaging, electroencephalography, computed tomography, and positron emission tomography, all of which can be used to study neurological and neuroanatomical abnormalities in the brains of individuals who have perpetrated homicide. Research has shown distinct neurological activity in individuals who have homicidal thoughts or who exhibit violent behaviors.
One perspective explicit in the call for integration of biological (e.g., genetic predispositions), psychological (e.g., psychological disorders), and social (e.g., poverty) explanations of homicide has been aptly named the biopsychosocial perspective. There are limitations to this theory because many of the bidirectional relationships between these three metafactors have not yet been fully explored. Although this is a promising theoretical position, a wealth of new research is yet to be conducted exploring the links between these factors. Inherited predispositions for particular personality disorders may influence how an individual is perceived and treated by others. The way an individual is perceived and treated by others provides a feedback loop, altering cognitions about relationships with others that can influence personality. In sum, there are numerous potential pathways to homicide, and we will be better positioned to expand on these interrelationships with future research.
In many of the cases, links between abnormal cognition and brain activity have been documented. Murderers have been diagnosed with psychological disorders such as antisocial personality disorder or other personality disturbances, psychological stressors, various types of childhood trauma, and drug and alcohol abuse problems. Not all these psychological disorders, however, apply to all killers. Many known factors combine to result in individual differences in brain patterns and cognition and complicate our understanding of the psychology of homicide. We believe that insight gained from various areas of the psychological and other behavioral sciences will provide greater clarity into the motivations and development of homicidal thoughts and behavior. Various theories have recently shed light on homicidal psychology in ways that have previously escaped psychologists.
Evolutionary Perspectives on Homicide
One particularly powerful theoretical perspective that has yielded insight has been the application of evolutionary perspectives to the study of homicide. An evolutionary psychological approach to homicide is relatively new and allows for stronger anchoring of the psychological sciences with the biological sciences. Evolutionary psychologists argue for distinctions between various types of homicide. Inroads into the psychology of homicide have been made by an attempt to understand the relationships between the victim and the offender. There is a debate among evolutionary psychologists on whether there exist evolved psychological adaptations for homicide or whether homicide occurs as a by-product of adaptations selected for in response to other sets of social adaptive problems (e.g., sexual jealousy, same-sex competition, aggression). An evolutionary psychological approach informs us of many areas in the psychology of homicide that have not been fully explored. If homicides were a recurrent feature of our ancestral environment, for example, selection would have favored antihomicide psychological adaptations (e.g., avoid being killed, minimize the threats posed by others). Research on the existence of these possible evolved psychological adaptations is currently under way.
In many homicides, the offender and the victim are individuals with a history of previously close romantic or familial relationships. There are many known factors linked with homicide among romantic partners, including sexual jealousy and prolonged abuse of women by their partners. These variables demand a deeper understanding of interpersonal relationships that can add to the body of research informing the psychology of homicide. A particularly dangerous time for many women comes when they terminate a romantic relationship. From an evolutionary perspective, this termination prompts psychological adaptations in men that may have functioned in ancestral environments to retain a mate. These adaptations may prompt behavior such as vigilance over the partner’s whereabouts, reassessment of the relationship, or, more dangerously, stalking behavior and homicidal rage over the termination of the relationship and a newly established relationship with a rival male.
Among homicides occurring between parents and children, men are more likely than women to kill their children when the children are older, whereas women are more likely to kill their children when the children are younger. Many of the results of analyses of filicides follow from predictions made by evolutionary psychologists. Men, relative to women, may harbor psychological adaptations that monitor genetic relationships between themselves and their putative children (e.g., cues such as female infidelity and their own similarity to the child). The features of homicides by mothers perpetrated against children are very different from those of homicides perpetrated by fathers against children. Mothers more often than fathers kill their children because of factors related to current states (e.g., absence of investing father, resource demands from children) or future prospects (e.g., bias toward future children rather than current children). Prior to the work done by evolutionary psychologists, no research platform had identified the presence of stepparents as a risk factor for child homicide. Researchers have documented a risk factor of filicide that is 100 times greater when a stepparent resides in the household.
Siblicides account for only 1% of all homicides, but analysis of this type of homicide has given us glimpses into the psychology of sibships. Among siblicides, for example, older siblings are more often the perpetrators earlier in life. In contrast, younger siblings are more often the perpetrators later in life—perhaps as an attempt to secure larger portions of inheritance that might otherwise be channeled to older siblings. Additionally, features of the precipitating conflict within the relationship may be revealed by the method of murder. Among siblings, for example, full siblings use a less brutal method of homicide than stepsiblings or half-siblings.
Future Directions and Integration
In addition to the theoretical strides that need to be made in the area, there are many empirical obstacles to be overcome. Data found in national and city-level homicide databases often do not contain enough information relevant for more detailed analyses of homicides. These obstacles are correctable with greater collaboration between law enforcement and social scientists. Another problem with our collective understanding of homicide is media misrepresentations. Those murder cases that are relatively rare (e.g., homicide of women and children, serial murders) are often the cases covered the most by different media sources. Very little is known by the public of the actual risk factors and probabilities of homicide.
The prospect of future research on the psychology of homicide is bright, with the overarching goal of understanding the biological, psychological, and social triggers producing homicidal cognitions and behavior. More detailed pictures of the minds of murderers will be made through the collaborative efforts of criminologists, sociologists, anthropologists, forensic psychiatrists and psychologists, neuropsychologists, clinical/counseling psychologists, and evolutionary psychologists. With such collaborative efforts focusing on the interplay between the biological, psychological, and social correlates of homicide, further refinement of existing theories will lead to future discoveries in the psychology of homicide.
- Bancroft, C. (1898). Subconscious homicide and suicide; their physiological psychology. American Journal of Insanity, 55, 263-273.
- Buss, D. M., & Duntley, J. D. (2006). The evolution of aggression. In M. Schaller, J. A. Simpson, & D. T. Kenrick (Eds.), Evolution and social psychology (pp. 263-285). New York: Psychology Press.
- Daly, M., & Wilson, M. (1988). New York: Aldine de Gruyter.
- Daly, M., & Wilson, M. (1997). Crime and conflict: Homicide in evolutionary psychology perspective. Crime & Justice, 22, 51-100.
- Nisbett, R. E. (1993). Violence and U.S. regional culture. American Psychologist, 48, 441-149.
- Smith, M. D., & Zahn, M. (2004). Homicide: A sourcebook of social research. Thousand Oaks, CA: Sage.
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