Crime and Conflict: Homicide in Evolutionary Psychological Perspective

Criminological theories are usually framed in sociological terms but always entail psychological assumptions. Psychological accounts, in their turn, entail assumptions about the adaptive “design” of evolved mental mechanisms and processes. Thus, explicit attention to recent theory and research on psychology and evolution can sometimes help criminologists generate productive hypotheses and avoid blind alleys. Homicide research is illustrative. Interpersonal conflicts are engendered by interactions among individuals whose psyches were designed by natural and sexual selection to make them effective competitors and effective nepotists (kin-benefactors). These considerations suggest numerous testable hypotheses about such matters as who is likely to kill whom, and how the demography of homicide perpetration and victimization is likely to vary among victim-killer relationships. An evolutionary psychological perspective inspires us to criticize recent criminological discussions of sex differences and age patterns in criminal offending, theories that contrast rational choice with emotional or impulsive behavior, and the medicalization of antisocial behavior as a pathology. Criminological theory is overwhelmingly and appropriately framed in sociological terms, but it always entails assumptions or postulates about human desires, developmental susceptibilities, and social inferences. In other words, sociological concepts and theories rest on models of human psychology, models that are often implicit and unexamined (MonMartin Daly and Margo Wilson are professors of psychology at McMaster University in Hamilton, Ontario, Canada. We thank John Monahan and Michael Tonry for comments on a draft of this essay and the Social Sciences and Humanities Research Council of Canada, the Harry Frank Guggenheim Foundation, and the Natural Sciences and Engineering Research Council of Canada for financial support ©1997 by The University of Chicago. All rights reserved. 0192 -3234/97/0022-0002$02.00 Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 52 ahan and Splane 1980) and sometimes obsolete. Attending to what psychologists have discovered about how people process information and select their actions can be a great aid to criminologists, including even those primarily interested in macrosocial phenomena. Psychological explanations, in their turn, rest on models of the functional organization of the human animal, and these models of our evolved “human nature” also warrant scrutiny. Attending to what evolutionists have discovered about the process that designed the human mind can be a great aid to psychologists in their investigations of the mind's structure and operations (Barkow, Cosmides, and Tooby 1992). Our thesis, then, is that the conceptual framework of evolutionary psychologists can be a valuable aid to criminological theory and research if criminologists can forsake disciplinary parochialisms and reflex denunciations of “reductionism.” Evolutionary psychology’s brand of reductionism is not simplistic. Quite the contrary, in fact, for it treats social influence as more complex than do prevailing criminological models. Seeing people as active agents with intricately structured information-processing abilities and self-interests, evolutionary psychologists are critical of approaches that treat them instead as little more than putty shaped by the statistical sum of their experiences. Influential treatments of the “subculture of violence” (e.g., Wolfgang and Ferracutti 1967) and of mass media effects on “imitative” violence (e.g., Phillips 1983; Baron and Reiss 1985), for example, are flawed by virtue of their reliance on an unrealistic, implicit model of the human animal as a passive recipient of cultural influence rather than its active interpreter (Daly and Wilson 1989). In these and other discussions of the social patterning of criminal violence, social influence is often conceptualized as the mere elicitation of an arbitrary, thoughtless conformity when the actual processes involved are likely to be subtler. A sensible man will be quicker on the trigger in what he perceives to be a relatively violent setting than in an apparently peaceful one, for example, not because he has become acculturated or has internalized local norms about the legitimacy of violence but because of a shift in the perceived risk of lifethreatening action by antagonists. For this sort of reason, the positive feedback of violence on itself, which is often blithely attributed to imitation or contagion or the reinforcing of norms, may be mediated by processes quite different than these terms imply. A more satisfactory account of “subcultural” and “imitative” effects must incorporate a specific characterization of the psychological processes by which the Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 53 effective variables influence individual actors. Nisbett and Cohen (1996) provide an outstanding example of such an approach with respect to regional differences in the legitimacy and prevalence of violence in the United States. In this essay we outline an evolutionary psychological perspective on conflicts of interest and criminal violations of other people's interests, with principal reference to research on homicide. We argue that certain patterns in the incidence of conflict and crime are predictable consequences of psychological processes that have been designed by the evolutionary process of Darwinian selection to make individuals effective competitors and effective “nepotists” (kin-benefactors) in ancestral environments. We argue that this perspective sheds light on the roles of certain demographic and situational variables, some but not all of which criminologists already consider important as risk factors for crime perpetration and victimization. We discuss sex differences in crime in the light of evolutionary understandings of what the malefemale phenomenon is fundamentally about, and we discuss age patterns in the light of evolutionary understandings of life span development. The school of criminological thought that is perhaps most congenial to this perspective is the “rational choice/routine activities” approach, but we suggest some caveats about “rationality.” In conclusion, we offer some suggestions for research that will more explicitly acknowledge that emergent group-level phenomena are both the products of interactions of numerous actors and a crucial part of the social and material environment affecting those actors. I. Crime and Conflict “Crime” is a socially constructed category of variable-specific content: acts that are deemed crimes in one time or place may be legitimate in others. It does not follow, however, that the set of things called “crime” is arbitrarily constituted. There is considerable overlap in the content of criminal codes, both written and traditional, from around the world. The acts that are most consistently criminalized are concentrated in a few principal domains: certain acts of violence, certain sexual acts, certain acts of expropriation, and certain betrayals of the collectivity to rival collectivities. In sum, crime consists overwhelmingly of self-interested action conducted in violation (or reckless disregard) of the interests of others. If criminal activity derives from interpersonal conflicts of interest, then criminological understanding would surely benefit from a sound Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 54 theory of the fundamental nature of self-interests (Cohen and Machalek 1988; Daly and Wilson 1988a, 1988b; Vila 1994; Machalek 1995). Where do interests overlap and where do they conflict? What are the determinants of variable inclinations to challenge rivals or to expropriate material resources? What qualifies as a crucial resource anyway, and why are even immaterial social resources such as status perceived as limited and worth contesting? These are questions that are addressed at a fundamental level by the emerging synthesis of evolutionary psychology. Whereas “interests” and “conflict” are conceived as group-level phenomena by many criminologists, evolutionists see each person’s interests as distinct and consider theories that analogize collectivities to individual actors to be flawed (see Sec. IIC below). The evolutionary conception of conflict is largely but not entirely a matter of resource competition. “Competition” refers to any conflict of interests in which one party’s possession or use of a mutually desired resource precludes another party’s possession or use of the same. This category clearly encompasses most of the criminal acts that are likely to be called “instrumental” or “rational,” but it also includes crimes that might be deemed “expressive” or “irrational.” Violence motivated by sexual rivalry is an obvious example. More subtle examples are the “face” and “status” disputes that constitute a very large proportion (perhaps the majority) of all U.S. homicides; the social resources contested in these cases are limited means to the end of more tangible resources (Wilson and Daly 1985). But not all conflicts are competitive according to the above definition. If a woman rejects one suitor for another, for example, then she and the spurned man have a conflict of interest, but they are not competitors, whereas the male rivals are. In general, competition is predominantly a same-sex affair because samesex individuals are usually more similar in the resources they desire than opposite-sex individuals. There is a rich body of evolutionary theory, discussed below, concerning the ways in which sex, age, and other factors affect the intensity of competition, and this body of theory sheds light on the sulking demographic patterning of crime. Although we believe that an evolutionary psychological approach is of broad applicability to the study of crime, we focus here on homicide. Homicide is in several ways the best prototype of crime. It is a major crime in all codes, exemptions of various forms of justifiable homicide notwithstanding. It stands at or near the top of everyone’s list of “serious” crimes. It is generally believed to be the most reliably detected and reported of crimes, hence the crime most amenable to unbiased Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 55 analysis of its correlates and putative causes. Finally, homicides are drastic resolutions of interpersonal conflicts and thus afford a window on the variable incidence and intensity of such conflicts. It is this latter idea–that homicide can be treated as a sort of “conflict assay” for testing theoretical ideas about the factors exacerbating or mitigating interpersonal conflict in particular relationship categories, life stages, and circumstances–that has inspired most of our own research on homicide, some of which is reviewed below. But before we get to matters of criminological substance, a general introduction to evolutionary psychology is required. II. Evolutionary Psychology In criminology textbooks, the word “psychology” is used mainly with reference to personal attributes that differ among individuals, and especially those attributes that may be interpreted as abnormal deficits or pathologies. However, the study of stable individual differences, pathological or otherwise, constitutes only a small part of psychological science and not the part of greatest relevance for understanding crime as a social phenomenon. A. Psychological Mechanisms and Processes Are Biological Adaptations Psychological science is primarily a quest to discover the mechanisms and processes that produce behavior and to characterize them at a level of abstraction that applies to everyone (or at least to everyone of a given sex and life stage). Psychology is closely related to physiology and neuroscience, but it is distinguished by its focus on an informational level of description: its constructs include memory encoding and retrieval, attention processes, recognition and categorization, attitudes, values, self concepts, motives, and emotions. When postulating such constructs, psychologists aim for a level of abstraction at which historical, cultural, and ecological variability can be explained as the contingent products of consistent panhuman psychological processes responding to variable circumstances and experiences. “Anger,” for example, is a motivational/emotional state that can be elicited in anyone, and that plays a role both in mobilizing physiological resources for violent action and in advertising one’s likelihood of engaging in such action. More controversially, perhaps, we propose that “male sexual proprietariness” is a sexually differentiated motivational/cognitive subsystem of the human mind, with behavioral manifestations that are culturally and historically variable but are nevertheless predictably related Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 56 to various aspects of the status and circumstances of the focal man, his partner, and his rivals. (This argument is developed in Sec. VIII below.) Basic psychological constructs like “color vision” and “self esteem” and “anger” and “sexual proprietariness” are putative components of human nature. Insofar as they are complexly organized, they are almost certainly biological adaptations: attributes that are effectively organized, as a result of a long history of natural selection, to achieve some useful function such as respiration or image analysis or the vanquishing of rivals. The proposition that some attribute is an adaptation is a hypothesis about special-purpose “design,” suggesting avenues of further inquiry (Williams 1966). Generating hypotheses about what such enigmatic lumps of tissue as the heart or lungs or liver are designed to accomplish were essential first steps for investigating their physiology and pathologies (Mayr 1983). The same goes for the successful investigation of mental “organs”: psychological mechanisms are designed to solve particular adaptive problems, and hypotheses about these adaptive functions give direction to the research enterprise in both obvious and more subtle ways (Daly and Wilson 1994a, 1995). A psychologist who assumes, for example, that the principal function of the psychophysiology of anger is to mobilize the organism for effective physical assaults will look for a somewhat different set of manifestations and social controls than another who instead assumes that anger functions primarily to threaten and deter so as to limit the costs of violent confrontations. The unwitting “designer” of adaptations–the “blind watchmaker” in Dawkins's (1986) memorable phrase–is Darwinian selection, the process that created existing adaptations in each living species as solutions to recurring problems confronted by many generations of its ancestors. These evolved solutions necessarily entail contingent response to environmental features that were statistical predictors, on average, of the fitness consequences of alternative courses of action in the past. (Darwinian “fitness” refers to reproductive posterity, or, somewhat more precisely, to the average success of a given phenotypic design in promoting its proportionate prevalence by promoting the relative replicative success of its bearer’s genes in competition with their alleles in the environments of natural selection.) It follows that evolutionary psychologists see no distinction in kind between “psychological” and “biological” phenomena. Influences and processes, which are best characterized at a psychological level (e.g., in Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 57 cognitive, interpretative, or experiential terms), are in incessant reciprocal interaction with the sorts of physiological states and processes commonly referred to as “biological” influences on behavior. Circulating blood levels of the male gonadal hormone testosterone, for example, have a variety of subtle effects on information processing and behavior, both by virtue of action in the central nervous system itself and by virtue of other peripheral effects, but testosterone levels are themselves affected by social experience and these effects are themselves affected by culturally specific considerations. A man’s perception that he has won in some sort of competition can lead to rapid elevations of circulating testosterone, even if the “competitions” are as arbitrary as a coin toss (McCaul, Gladue, and Joppa 1992) or as cerebral as a chess game (Mazur, Booth, and Dabbs 1992). Moreover, in one experimental study, an insult that engendered a surge of testosterone in men raised in the “honor” culture of the south in the United States, in which retaliatory aggression is admired, had no such influence on men raised in the north, where it is not (Nisbett and Cohen 1996). Thus psychophysiological adaptations often entail contingent response not just to immediate circumstances but also to the cumulative consequences of experience, including the assimilation and internalization of local cultural norms. Discussions of criminal violence are frequently couched in the language of pathology. This is an appropriate framework insofar as violence is associated with alcohol-induced psychoses, delusions, and organic defects, as may often be the case (e.g., Raine 1993; Giancola and Zeichner 1995; Aarsland et al. 1996), but the language of pathology can mislead. Violent behavior is abhorrent, but that does not mean that violence is a pathology (Monahan and Splane 1980; Cohen and Machalek 1994). Pathologies are failures of anatomical, physiological, and psychological adaptations as a result of mishap, senescent decline, or subversion by biotic agents with antagonistic interests, failures that reduce the adaptations’ effectiveness in achieving the functions for which they evolved (Williams and Nesse 1991). Violence cannot in general be explained as a maladaptive byproduct of such failures since people and other animals possess complex psychophysiological machinery that is clearly designed for the production and regulation of violence. The evidence of functional design in the psychophysiology of violence is diverse. In the first place, its elicitors are typically threats to survival and reproduction, and its effects are typically to counter those threats. Animals (including people) react violently to usurpation of esMartin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 58 sential resources by rivals, and they direct their violence against those rivals (Huntingford and Turner 1987; Archer 1988). Behavioral ecologists have analyzed the cost-benefit structure of confrontational violence in terms of the conditional determinants of the expected consequences of fight versus flight and of escalation (e.g., Andersson 1980; Enquist and Leimar 1990; Colegrave 1994), and they have assessed whether animals actually behave in ways that are contingent on available cues of the probable costs and benefits of alternative actions (e.g., Chase, Bartolomeo, and Dugatkin 1994; Pruett-Jones and PruettJones 1994; Turner 1994; Kvarnemo, Forsgren, and Magnhagen 1995). These analyses leave little doubt that violent interactions are regulated with sensitivity to probable consequences. In addition to contextual appropriateness, the motivational states of angry arousal entail postures appropriate for attack and defense and complex psychophysiological mobilization for effective violent action and for the temporary suppression of potential interference from other adaptations such as pain sensitivity. Animals exhibit diverse morphological structures that function solely or primarily as intraspecific weapons, and these are often sexually differentiated and characteristic of delimited life stages. There is neural machinery dedicated to aggression and this too is often sexually differentiated. Moreover, the sexual differentiation of physical aggression is itself variable across species, and the magnitude of sex differences in both overt weaponry and intrasexual aggressive behavior is systematically related to other variable aspects of social ecology (Daly and Wilson 1983). All of these facts testify to the potency of Darwinian selection in shaping the anatomy and psychology of intraspecific violence. The misconception that human violence is merely pathological has perhaps been reinforced by studies linking it to disadvantaged backgrounds and environments. But these associations are by no means universal. In nonstate societies, like those in which the human psyche evolved, skilled violence was a prominent attribute of high-status men and a contributor to their success (Betzig 1986; Chagnon 1988, 1996). In modern state societies, the welfare of most people no longer depends on their own or their allies’ violent capabilities, so violence is relatively rare and relatively likely to reflect psychological pathology. Nevertheless, disproportionate numbers of violent offenders are drawn from groups who lack access to the opportunities and protective state services available to more fortunate citizens, and who therefore find themselves in “self-help” circumstances much like those experienced Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 59 by most of our human ancestors. It is not at all clear that violence in such circumstances is usefully deemed pathological. Moreover, even in other circumstances, and even where violence is associated with an organic defect, there remains a functional organization to its contingent controls. B. Evolutionary Psychology Is Not a Monolithic Falsifiable Theory but a Framework for Generating Theories Science is a self-correcting, cumulative enterprise whose practitioners routinely and appropriately try to formulate mutually exclusive alternative hypotheses and revise their models to accommodate unexpected findings. Ironically, however, when evolutionists engage in these ordinary scientific practices, they are apt to encounter accusations of engaging in untestable pseudoscience. A common misunderstanding, even among self-styled “evolutionary psychologists,” is that “the evolutionary hypothesis” about sex differences or the age-crime relationship or whatever can and should be tested against “nonevolutionary” alternatives. But there is no single, privileged “evolutionary hypothesis” about any of these phenomena, and the only currently available alternative to the theory of evolution by selection is creationism, which is pseudoscience (see, e.g., Futuyma 1983). Evolution is “just a theory” in exactly the same sense as the atomic theory is just a theory. The proposition that the human animal and its psyche evolved under the influence of selection is a “fact” in the same sense (and as well established) as other scientific propositions at some remove from direct observation, such as the fact that brains process information or the fact that molecules are comprised of atoms. The alternatives to a particular evolutionary hypothesis are other evolutionary hypotheses. Like other animals, human beings can be analyzed into subsystems that perform distinct tasks: respiration, learning, digestion, visual scene analysis, and so forth. These separate tasks are carried out by their separate bits of anatomical, biochemical, and psychological machinery, in the service of a functionally integrated, higher-order, organismic agenda. And what is that agenda? To manufacture additional, similar animals. This is the single superordinate “purpose” that natural selection, the process responsible for the fact that we possess complex adaptive attributes, designed them to achieve. We have placed the word “purpose” in quotation marks because it is important to stress that fitness is not literally an objective. The goals that animals (including Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 60 people) have evolved to monitor and pursue are more immediate things like full bellies and sexual satisfaction. Evolutionists often say that functionally integrated systems with many parts and actions constitute a “strategy.” Elements in a particular flowering plant’s “reproductive strategy,” for example, might include sprouting in response to a threshold soil temperature, flowering at a certain day length, and maturing of the female parts of its hermaphroditic flowers before its male parts. The metaphorical nature of the language of strategy is obvious here; no one imagines that the plant has intentionality. Where this metaphor can be misleading is in the case of animals’ evolved strategies since one may slip unwittingly from claims about what the organism is “designed” to achieve into claims about what it is “trying” to achieve. This is especially problematic in the case of the human animal. In other words, the purpose-like functionality of adaptations invites an uncritical equation between intentions, goals, and ambitions, on the one hand, and adaptive functions, on the other. Consider the idea that sexual motivation has evolved “to” promote reproduction. Several writers have erroneously taken this to imply that people must have evolved to pursue reproductive ends with strategic flexibility, and that evolutionists should therefore expect contraception to be eschewed unless it can be used as a means of allocating reproductive efforts to increase the numbers or improve the circumstances of one’s young. By similar logic, voluntary childlessness and vasectomy have been cited as evidence against “the evolutionary hypothesis.” But it should be obvious that evolved adaptations can be expected to be reproductively effective only in environments that are not crucially different from those in which the relevant history of natural selection took place (Symons 1990; Tooby and Cosmides 1990b). Thus, even a convincing demonstration that the innovation of modern contraception has left people blithely pursuing reproductively ineffectual objectives would in no way challenge the proposition that humann sexuality is a complex psychological adaptation for the promotion of fitness. The point here is that fitness plays a different role in evolutionary theory from the role that homeostasis or self-esteem or other monitored target states play in physiological and psychological theories. When the fitness consequences of behavior are invoked to explain it, they are properly invoked not as wants or goals but as explanations of why particular proximal objectives and motivators have evolved to play their particular roles in the causal control of behavior, and why they Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 61 are calibrated as they are. When male birds continuously follow their mates closely during the breeding season, for example, ornithologists interpret the behavior as mate-guarding and its fitness-promoting function as paternity assurance. These interpretations have inspired many testable hypotheses about the contingent causal control of behavior: mate-guarding has been found to vary in relation to several cues of the onset of female fertility, and to vary in relation to the proximity, abundance, and attractiveness of male rivals, for example, while the male’s success in keeping his mate under guard has been found to be predictive of his subsequent level of participation in the care of his putative offspring (Davies 1992; Møller 1994). These facts were discovered as a direct result of theorizing that the adaptive function of the mate-guarding psychology of male birds resides in paternity assurance, and yet the bird neither knows nor cares about paternity per se. Genetic posterity or fitness can be deemed the superordinate “purpose” of evolved psychologies, then, so long as the implication of functionality without intentionality is understood. But what use is it to identify superordinate purpose in this way? The very generality of the idea that reproductive posterity is the distal function of all adaptations may make it seem uselessly vague. Commanded by Darwinian gods to go forth and multiply, a dutiful Eve might sensibly ask, “But how, exactly?” So lets analyze Eve’s task, from the top down rather than from respiration, et cetera, up. People are manufactured out of other substances, so Eve's task immediately resolves itself into two major subtasks: garner the resources necessary for reproduction and convert those resources into more people. Moreover, making “more people” doesn't mean just any people. The specific adaptive attributes favored by selection are necessarily those that have somehow effectuated their own proliferation relative to alternative attributes within the same population. Thus, the people whose survival and reproduction our minds and bodies have evolved to promote are our descendants and other blood relatives. Although people often find common cause and cooperate with nonrelatives, and although there is a body of evolutionary theorizing concerned with such “reciprocal altruism” (Trivers 1971; Alexander 1987), shared interests and solidarity are most readily attained and maintained among blood kin. Moreover, all the males in a population have always been engaged in a sort of zero-sum game for the paternal half of the ancestry of future generations, while the females were playing a parallel game for the maternal half. Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 62 These considerations put a different gloss on the “two major subtasks” mentioned earlier. What people and other creatures must have evolved to do is to be effective competitors in intrasexual competition for essential reproductive resources in the social and material environments of selection, and to be effective “nepotists” in those environments (Hamilton 1964). And what they have certainly not evolved to do is to promote “the reproduction of their species,” as a prominent misunderstanding of natural selection would have it. C. Groups Are Not Individuals Social scientists have repeatedly promulgated theories in which various characteristics of individuals–intentions and preferences, ambivalences, health and pathology, homeostatic regulation, and so forth– are attributed to collectivities. An evolutionary perspective suggests that such theories constitutes a weak metaphor, at best. Evolutionary psychology and behavioral ecology began to flower only after a common fallacy, dubbed “greater goodism” by Cronin (1991), was dispelled. For 100 years after Darwin, most biologists had uncritically assumed that natural selection equips animals with the shared purpose of “the reproduction of the species.” This assumption was wrong (Williams 1966). Natural selection is a matter of differential reproductive success, and it has consistently favored those individual attributes most effective in out-reproducing alternative attributes within the same population. The attributes that succeed by this criterion are not necessarily those that will best promote the population's welfare or persistence. Decades of theoretical and empirical work on “levels of selection” in biology (see, e.g., Dawkins 1982, 1986; Cronin 1991) have confirmed and clarified why the individual organism is the primary locus of complex integrated selfinterest in the hierarchy of life. (The reason why the main locus of integrated self-interest does not reside at a level below that of the individual is that the expected fitnesses of an individual’s organs or cells or genes are for the most part isomorphic with the whole organism’s expected fitness, so selection favors those suborganismic elements that maximize this quantity at the organismic level. There are, however, important exceptions at the genetic level [see, e.g., Cosmides and Tooby 1981; Dawkins 1982; Haig 1993].) Attempts to understand the behavior of societies, classes, cohorts, and other collectivities confront a special problem. The human mind is marvelously adept at constructing mental models of the agendas and Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 63 likely actions of intentional agents like ourselves. We apparently owe this talent to an evolved psychological mechanism, our so-called theory-of-mind module (e.g., Leslie 1992; Premack and Premack 1995). This extremely sophisticated cognitive device infers the idiosyncratic details and interconnections of the beliefs, plans, and intentions of each person we have to deal with, on the basis of that person’s known history of actions and on the default assumption that his or her mind is like our own in its elements and rules but not in its detailed contents. The theory-of-mind module is essential for normal social functioning, and insight into its workings has been gained partly from study of the severe disability of those in whom it is defective or lacking, namely, autistics (Baron-Cohen 1995). It is obviously enormously useful to be able to anticipate the actions of other people by consulting a model of how what they know and don't know, what they want, and what they believe will interact and affect their actions. An apparent byproduct of this useful talent, however, is a (usually harmless) tendency to misapply the same sort of thinking to entities that are not intentional agents, such as computers or cars or “society.” In Canada, we are treated to an example of this sort of fallacious thinking whenever there is a multiparty election in which no party wins a majority of the parliamentary seats. Pundits can be counted on to explain that a disgruntled or skeptical public, trusting none of the contending parties to govern fairly or effectively, has expressed its preference for a minority government instead. We hope that the spuriousness and obfuscation produced by reifying the “body politic” is transparent in this case. The mere fact of a split vote provides no evidence about disgruntlement, skepticism, or trust on the part of anyone nor does the election of a minority government necessarily correspond to anyone’s preferred result. Social scientists are not immune to this sort of fallacious thinking. Treating “the patriarchy” as a cohesive, intentional agent, for example, clarifies nothing about conflict and power relations between the sexes while obscuring the relevance of men’s conflicts with one another to their inclinations to control their wives coercively (see Sec. VIII below). Other cases are subtler. Discussions of “social disorganization,” for example, may invoke the capacity of large amorphous segments of society, such as classes or subcultures, to “regulate themselves,” piling one weak metaphor on another. Genuine “regulation” of perturbations is an attribute only of systems with a unity of purpose, an attribute “designed into” the system either by natural selection or by an intenMartin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 64 tional agent. “Social pathology” is similarly metaphorical, for as noted above, a genuine pathology is something that compromises a functionally united entity’s capacity to do what it evolved to do. Individual organisms and their constituent parts have evolved to do many specific things, but collectivities above the level of the individual organism are not, in general, specifically organized to accomplish anything in particular (Williams 1966). Clubs, political parties, and other human organizations formed for common goals are conspicuous exceptions to this generalization. But classes, subcultures, and societies are not. Applying individual-level concepts like desire or preference or pathology to group-level entities whose unity of purpose does not approach that of individual organisms virtually guarantees that their causal dynamics will be misrepresented. When one speaks of what “society” encourages or what “the patriarchy” schemes to achieve, for example, one obscures the complexity of social processes and the ubiquity of conflicts of interest. This is not to say that groups qua groups have no properties worth talking about. But group-level properties are emergent and distinct from those of their constituent individuals. A society or polity or occupational group or class does not have preferences or intentions or pathologies. It has institutions, balances of power, a greater or lesser degree of consensus on each issue, and a certain distribution of wealth, among other things. D. Evolutionary Psychology Is Not Behavior Genetics As we noted earlier, psychological science is primarily concerned with the mechanism and processes that all normal individuals share, and this is equally true of evolutionary psychology. It is a fact that individuals respond differently to identical environmental inputs from the earliest developmental stages, and that some of that diversity is due to genetic differences. However, the notion that such genetic diversity is of central interest to evolutionists is a misconception. Behavior genetics is the scientific discipline concerned with analyzing the degree to which behavioral differences between individuals within populations can be traced to genetic differences. This field has been largely isolated from evolutionary psychology (and behavioral ecology and sociobiology), whose main concerns are mental mechanisms and processes that are shared by all normal individuals, generating behavioral variation as contingent response, both immediate and enduring (developmental), to social and other environmental variation (Crawford and Anderson 1989; Daly 1996). Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 65 Confusion on this point derives largely from a mistaken belief that evolutionary psychological hypotheses imply that one should be able to discover genes “for” generating the proposed adaptations. Geneticists are able to identify genes that code “for” an attribute when some individuals have the gene and the condition while others do not, that is, when the attribute is “heritable.” An example is the rare MOA1 gene associated with impulsive violence, discovered by Brunner et al. (1993). However, the adaptations of interest to evolutionary psychologists are typically universal, and there is no reason to expect that there will be detectable heritable variation in their expression. Thus, although it is often asserted that hypotheses about evolved adaptations imply that heritability should be appreciable and demonstrable (e.g., Sussman, Cheverud, and Bartlett 1995), just the opposite is true. A substantial amount of heritable variation is prima facie evidence that the attribute under consideration is selectively neutral and hence not an adaptation at all (Falconer 1960). It is no accident, for example, that the variable attribute of our eyes that is most highly heritable, namely the color of the iris, plays no part in vision. Perhaps evolutionary adaptationist hypotheses are so often misconstrued as hypotheses about behavior genetics because they invoke hypothetical genes “for” behavioral and psychological attributes in their theories. The point of such theories is not, however, to trace observed behavioral variation to genetic differences. Rather, population genetical models are used to address how selection would be expected to shape a given trait if minor, rare heritable variants were to arise (as they evidently do with respect to almost any quantifiable trait), and to predict what forms and magnitudes of the selected traits would be expected to become species-typical over evolutionary time. But since selection is constantly removing suboptimal variants (such as the deficient MOA1 gene that Brunner et al. [1993] found in a single human lineage), the residual heritable variation of any trait with important fitness effects is likely to be negligible. Thus notwithstanding the genetical language, both theory and research in evolutionary psychology and behavioral ecology are directed toward the discovery of species-typical adaptations, and these are often expressed as contingent decision rules. For example, “mate-guarding” behavior varies among the mated males of a given bird species (and, no doubt, among human males as well), and this variation is intelligible as the product of a common psychology with contingent decision rules: the males respond to “bachelor pressure” as cued by one’s encounter Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 66 rate with lone males and to various other “risk”’ factors (e.g., Møller 1994). For this reason, environmental rather than genetic sources of behavioral variation provide the crucial tests of evolutionary psychological hypotheses (Crawford and Anderson 1989). III Who Victimizes Whom? The preceding introductory overview is all the evolutionary psychology one needs to approach some criminological issues in a fresh way. An exemplary topic is family violence (Daly and Wilson 1988a). According to current understandings of the evolution of social motives and behavior, the basic appetites, aversions, motives, emotions, and cognitive processes characteristic of any species, including Homo Sapiens, have been shaped by natural selection to produce social action that is effectively “nepotistic”: action that promotes the persistence of the actor’s genetic elements in future generations by contributing to the survival and reproduction of the actor’s genetic relatives. It follows that the basic psychological processes underlying solidarity and conflict in any social species should include processes that typically function to engender discriminative behavior in relation to genetic relatedness, and such processes indeed abound. Theory and research are in accord: other things being equal, cues that are ordinarily indicative of genetic relationship may be expected to mitigate animal conflict, and there is abundant evidence that they do (see, e.g., Hepper 1991). In light of the ubiquity of nepotistic solidarity in the animal kingdom, some prevailing notions about intrafamilial conflict and violence in the human animal seem more than a little odd. Freudians would have us believe that the urge to kill one's father is a universal element of the human male psyche, and the claims of some family violence researchers are scarcely less astonishing. According to Gelles and Straus (1985, p. 88): “With the exception of the police and the military, the family is perhaps the most violent social group, and the home the most violent social setting, in our society. A person is more likely to be hit or killed in his or her home by another family member than anywhere else or by anyone else.” To an evolutionary psychologist, these assertions are too surprising to escape critical scrutiny. The first concept needing scrutiny is “family.” Following Marvin Wolfgang (1958), homicide researchers have typically partitioned the victim-killer relationship into three categories: stranger, acquaintance, and relative. However, the third of these is far too general, encomMartin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 67 passing relationships whose qualitative distinctions greatly surpass those distinguishing “strangers” from “acquaintances.” The evolutionary psychological basis of the parent-child relationship, for example, is different from that characterizing the marital relationship since parent and child are genetic relatives with an indissoluble overlap in their fitness prospects whereas a comparable overlap in the expected fitness of marriage partners is predicated on reproduction and sexual fidelity. It follows that the specific potential sources of conflict in these two “family” relationships are utterly different, and the risk that conflict will become violent is vastly different, too (Daly and Wilson 1988a, 1988b). In addition to calling prevailing taxonomies of relationship into question, these considerations raise the issue of “opportunities” for violence as a result of routine activity patterns. In the report of a U.S. presidential commission on “causes and prevention of violence,” Goode (1969, P. 941) posed the question, "Why do intimates commit violence against one another?” and replied, “Perhaps the most powerful if crude answer is that they are there.” This appeal to differential opportunity is true as far as it goes, but it begs the question of whether relationships are differentially risky when opportunity is controlled. Goode implies that they are not, especially if the concept of opportunity is extended to encompass the intensity of interaction as well as its frequency: “Moreover, again crudely but reasonably, we are violent toward our intimates–friends, lovers, spouses–because few others can anger us so much. As they are a main source of our pleasure, they are equally a main source of frustration and hurt.” Is such an analysis adequate? Or do the distinct sorts of “intimate” relationships differ in ways that are not simply a matter of differential opportunity, as an evolutionary theoretical analysis of relationships would lead us to expect? (Suspicion should be aroused by the omission of “children” from Goode's list of “intimates.” Its words surely apply to them at least as much as to “friends,” but perhaps the distinctive quality of parentchild intimacy is too obvious to ignore.) One way to try to control for opportunity is to assess the incidence of violence between members of the same household, using information on the living arrangements of the population-at-large to specify the universe of potential victim-offender pairs. Daly and Wilson (1982) performed such an analysis of homicides in Detroit, with the results portrayed in figure 1. Clearly, Goode’s analysis was not adequate. Coresiding persons who were not genetic relatives experienced a hoMartin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 68 micide rate more than eleven times greater than coresiding kin. Moreover, although so-called family homicide is seen to be mainly marital homicide, the risk incurred by other sorts of unrelated coresidents (roommates and boarders) was just as extreme and greatly exceeded the risk in more “intimate” family relationships, in apparent contradiction to Goode’s invocation of intimates’ special ability to evoke anger. The more general points that figure 1 illustrates have been upheld in a variety of analyses of data from a variety of societies: kinship softens conflict, and the qualitative distinctions among relationships cannot be captured in simple dimensions like opportunity or intimacy (Daly and Wilson 1988b). The substance and intensity of conflicts are relationship-specific because particular social relationships–parent and child, spouses, unrelated friends, sexual rivals, and so forth–differ in their particular sources of potential and actual concordances and discrepancies in desired states of affairs. Failures of reciprocation are common sources of conflict in virtually Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 69 all relationships, for example, but not in the parent-child relationship, which is uniquely characterized by an unbegrudged one-way flow of resources. Instead, parent-offspring conflicts tend to revolve around an issue peculiar to that relationship, namely the allocation of parental resources among offspring (Trivers 1974); this insight predicts and explains much about the peculiar epidemiology of infanticide and other kinds of parentally perpetrated violence (Daly and Wilson 1988a, 1995). Other relationships have their characteristic conflicts, too. When men kill their brothers, the usual issue of contention is the partitioning of familial resources, whereas when they kill their brothersin-law, other issues, especially the mistreatment of the person’s sister by her husband, predominate (Daly and Wilson 1988b). And in violent marital conflict, the bones of contention, and hence the demographic risk markers, are different again (see Sec. VIII below). IV. Differences in Competition and Violence Most lethal violence occurs not within the family but between unrelated acquaintances and strangers, and much of this violence arises in the context of competition for material goods and more intangible resources like face and status. Competition is predominantly a same-sex affair, and variations in rates of homicide involving unrelated same-sex persons can be considered a sort of assay of competition’s local intensity (Daly and Wilson 1988b). Thus inequitable resource distribution obviously affects the local level of competition, and as we would expect, it is also a predictor of homicide rates (Krahn, Hartnagel, and Gartrell 1986; Hsieh and Pugh 1993), with same-sex nonrelative cases constituting the component of the homicide rate that varies most between times and places (Daly and Wilson 1988b). But whereas prevailing intensities of competition and gross rates of homicide are hugely variable in time and space, one difference is apparently universal: men kill unrelated men at vastly higher rates than women kill unrelated women, everywhere (see table 1). Criminologists and other social scientists have offered a wide range of hypotheses to explain sex differences in the use of lethal violence. Unfortunately, most presuppose the psychic identity of the sexes and are clearly unsatisfactory. Many writers have attributed men’s greater use of violence to some local aspect of one or another particular society, providing no candidate explanation for the phenomenon’s crosscultural generality (see Daly and Wilson 1988b, pp. 149-61). Others have invoked men’s greater size and strength, but while this asymmetry Martin Daly & Margo Wilson (1997). Crime and Conflict: Homicide in Evolutionary Psychological Perspective. Crime & Justice, 22, 51-100. 70 TABLE 1 Numbers of Same-Sex Homicides in Which Victim and Killer Were Unrelated: Various Studies Location/Society Periods of Study Male Female Chicago Detroit Miami Canada England and Wales Scotland Iceland A Mayan Village (Mexico) Bison-Horn Maria (India) Munda (India) Oraon (India) Bhil (India) Tiv (Nigeria) BaSoga (Uganda) Gisu (Uganda) BaLuyia (Kenya) Banyoro (Uganda) JoLuo (Kenya) Alur (Uganda) !Kung San (Botswana) 1965-81 1972 198