Conflict and Aggression

Cris Campbell. 21st Century Anthropology: A Reference Handbook. Editor: H James Birx. Volume 2. Thousand Oaks, CA: Sage Reference, 2010.

Humans, it often seems, are creatures of conflict. Without doubt, the annals of history bear stark witness to the reality of human aggression. By most measures, human conflict and aggression have directly or indirectly resulted in hundreds of millions of deaths over time. If mute statistics had explanatory power, then the inevitable conclusion would be that humans are by their natures irredeemably aggressive. This aggression, in turn, is at the heart of perpetual conflict. Certainly, this view has long been dominant in the West, where the biblical story of human corruption in the Garden of Eden has been a powerful and enduring influence.

Anthropology’s particular approach to the related topics of conflict and aggression is biological and cultural, or biocultural. Humans are, first and foremost, animals that have evolved over many millions of years. This evolutionary history has present consequences, not the least of which is that humans are in many ways determined and constrained by their biology. But that is not all. As humans evolved, they developed tools, technologies, language, and knowledge which, taken together, are called culture. These processes were not, of course, separate. Physical change led to cultural change and cultural change promoted physical change. This synthetic process of coevolution has produced the most cultural and potentially aggressive of all animals.


During the millennia dominated by Christian and scholastic thought, no one contemplated prehistory. Indeed, there was no such thing because it was believed that everything began with Genesis. Human nature was a settled issue. Over time, however, an increasing awareness of antiquity caused some to question the received biblical account. These thinkers began wondering about human life and society before the appearance of the first civilizations in Mesopotamia, Egypt, and Greece. One such person was Thomas Hobbes, and another was Jean-Jacques Rousseau. Between them, Hobbes and Rousseau established two sharply conflicting—and long-persisting—views of what human life had been like in the prehistoric past. Contained within each view is an assessment of essential human nature.

In 1651, Hobbes published Leviathan, a foundational work of political philosophy in which he argued that strong and centralized governments are essential to human well-being. Hobbes’s entire argument hinged on his belief that humans are aggressive and forever in conflict. Projecting this belief back in time, he envisioned a dark and misty prehistoric past in which humans were perpetually at war. Hobbes called this imaginary time and place the “state of nature.” For Hobbes, life in a state of nature was bleak, brutal, and brief. Humans without government were in constant conflict. The operative assumption for Hobbes is that humans are by nature aggressive, and in the absence of governing authorities, will engage in conflict.

In 1762, Rousseau published The Social Contract, another foundational work of political philosophy. While advocating for certain forms of government, Rousseau outlined his own vision of humans in a prehistoric state of nature. As Rousseau imagines things, resources are plentiful and humans peaceful. It is society itself—a movement away from a state of nature—that corrupts and causes conflict. From this, later writers conjured the idea of the “noble savage,” people who lived harmoniously in a time before society and government. For Rousseau, humans are not by nature aggressive and are drawn into conflict only by dysfunctional societies.

Although these competing visions were purely speculative, they proved exceptionally influential and remain so today. Most modern forms of government are founded, in theory if not in practice, on an allegiance to one of these two visions. Rousseau’s ideas continue to inspire all manner of utopian idealists, while Hobbes’s thinking continues to legitimate all forms of centralized authority. This continuing influence is remarkable, considering that neither Hobbes nor Rousseau knew anything about the prehistoric past or peoples. It was not until science began its slow assault on the unfettered imagination that others began to question these two visions of the past.

Evolutionary Foundations

In 1859, the publication of Charles Darwin’s On the Origin of Species forever changed the way humans viewed themselves. Besides discrediting the notion of a special creation, Darwin also undermined purely speculative assessments of human nature. Although the Origin and Darwin’s later work, The Descent of Man (1871), firmly placed humans in the animal kingdom, this placement was not without its own set of ideas about the humans living in a state of nature. Darwin came of age in a time of great intellectual ferment, and the classical economic works of Adam Smith and David Ricardo shaped many of the debates. Unsurprisingly, the topics of competition and conflict were prominently featured.

Despite being couched in the language of economy and markets, Victorian ideas about nature ultimately remained rooted in Hobbes, whose bleak assessment of prehistory was based on his belief that all resources were scarce in a state of nature. In the absence of governments, this scarcity results in “war of all against all.” Thomas Malthus, an English demographer and political economist, shared Hobbes’s assumption that prehistoric societies suffered from scarcity. Consequently, population sizes were limited. Over time, advances in technology increased production of foodstuffs, which in turn caused population growth. This growth created additional subsistence demands, in effect creating a positive-feedback loop involving improved technology, increased population, and intensified production. It was this process that caused Adam Smith to theorize that competition was the driver of all progress.

Darwin was familiar with these ideas and it was upon reading Malthus that the theory of evolution through the process of natural selection crystallized in his mind. All organisms are driven to reproduce, and this imperative causes a constant increase in numbers. Because resources are limited, competition ensues. Only the most fit survive and reproduce. This competition and struggle occurs not only within species, but also across species. Those traits that enable an organism to survive are favored and passed along through reproduction. Natural selection described a harsh nature “red in tooth and claw.” Although Darwin might have found a certain grandeur in this view of life, others were less sanguine. On close examination, the “new” Darwinian perspective did not really seem all that different from older biblical or Hobbesian ones—humans were condemned to a life of struggle, filled with both conflict and aggression.

Early Anthropological Views

After centuries of speculation about prehistoric humanity, Darwin finally had provided a theoretical framework within which this issue could be considered scientifically. In the decades following publication of the Origin, anthropology was founded as a discipline. In Britain, Edward Tylor applied evolutionary principles to culture and began assessing archaeological evidence of the past. In America, Lewis Henry Morgan studied native cultures and became a pioneer in ethnographic methods. Not surprisingly, neither Tylor nor Morgan was able to shake free of past prejudices, including those holding that prehistoric humans lived in near perpetual conflict. Both used words like primitive, savage, and barbaric to describe such early humans. The aggressive connotations were unmistakable.

During the first half of the 20th century, anthropologists largely busied themselves traveling the globe in search of little-known or unknown societies. The societies they studied were variously characterized as native, primitive, indigenous, and almost without fail warlike. That early 20th-century ethnographers should find aggression and conflict in the peoples they studied is hardly surprising. These anthropologists, after all, came from state-level societies in which aggression was considered natural and conflict inevitable. These anthropologists may have been looking in a refracted mirror, with the horrors of two world wars serving as background. Though with some notable exceptions (such as Margaret Mead’s pacific account of Samoan society), early ethnographies emphasized the aggressive natures of traditional peoples and highlighted their conflicts.

On the human evolutionary front, things were not much different. Although enigmatic Neanderthal fossils had been turning up in Europe since the late 1800s, no one at that time understood how they related to human evolution. In 1924, Raymond Dart’s description of the Taung child (Australopithecus africanus) was the first of many hominid fossil finds in Africa. As these fossils accumulated, a basic understanding of human evolution began to emerge. With the exposure of “Piltdown Man” as a forgery or hoax in 1953, anthropologists began to accept the fact that australopithecines were ancestral to Homo. Dart, who had earlier come to this view, had by this time developed his own detailed and speculative vision of australopithecine life.

Dart initially had hypothesized that australopithecines were savanna scavengers; however, his subsequent examination of all the fossils associated with australopithecines caused him to conclude they must have been hunters. But these were not ordinary hunters—they were bloodthirsty killers. Dart noted that not only were many of the australopithecine skulls dented and crushed, but also that surrounding fossil bones were broken and damaged. For him, these were certain signs of hunting and butchery. Australopithecines thus became, at least in Dart’s mind, vicious predators who used bones as weapons and tools. He even coined a name for this behavior and activity, calling it osteodontokeratic culture. It apparently never crossed Dart’s mind, as it did later examiners of the same fossils, that the bones had been gathered and processed by two of Africa’s most common predators— leopards and hyenas.

Although Dart’s hypothesis failed to make headway in the scientific community, it captured the imagination of Robert Ardrey, a popular playwright and unlikely figure in the history of anthropology. After spending some time with Dart, Ardrey became a believer. Not only did he accept Dart’s ideas; he also decided that the story needed to be told. Human ancestors as killer apes certainly made for good copy, and was entirely in keeping with a long line of thinking regarding human nature and prehistory. In 1961, Ardrey published African Genesis: A Personal Investigation Into the Animal Origins and Nature of Man, a best-selling book that shaped both public and scientific opinions regarding human nature. Ardrey argued that human ancestors could be distinguished from other primates primarily by the increased amount of aggression that is required for predation and hunting, which he identified as the key characteristic and defining feature of hominids.

Dart and Ardrey’s shared vision of human ancestors as killer apes corresponded well with a biblically rooted tradition that became secular with Hobbes and scientific with Darwin. This traditional view received further support from the influential papers and ideas emanating from the 1966 symposium titled Man the Hunter. The anthropologists and primatologists who attended were nearly unanimous in concluding that hunting—with its attendant aggressive impulses and territorial conflicts—was the key to prehumanity and prehistory. Because anthropologists had phylogenetically linked humans to other primates and considered humans to be apes, it was only natural to begin looking for clues to human behavior in other species, including nonprimates.

Coincident with the Man the Hunter conference in 1966, Konrad Lorenz published his famous book On Aggression. Although Lorenz was a zoologist and a founder of ethology (the study of animal behavior), his observations and conclusions substantially influenced scientists of all stripes, including anthropologists, primatologists, and psychologists. Over several decades, Lorenz had recorded animal behaviors across many species. He interpreted his observations through a distinctly evolutionary lens, one which construed animal behaviors as contributing to the twin imperatives of survival and reproduction. Of the several instinctive behaviors Lorenz identified, aggression was paramount. The more familiar form of aggression occurred across species, interspecific, and was nearly always associated with predation. Aggression within species, intraspecific, was less familiar but nearly always associated with access to essential evolutionary resources—food and mates. The latter was a particularly important source of aggression in males, who often had to fight for access to females. Animal territoriality implicated both types of aggression; space was taken and defended because it provided access to food (survival) and mates (reproduction).

Whether as a result of religious belief or philosophical dualism, humans have long been kept separate from animals. After Darwin, this separation became difficult to maintain, and as our knowledge of other species increased over time, the lines between human and animal became blurred, if not obliterated. As a result of Lorenz’s pioneering work, human conflict and aggression could be viewed more dispassionately, and without the distorting cultural fog that afflicts the study of so many things human. With empirical observation at the forefront, behavior could now be assessed within a Darwinian framework relatively free from metaphysical, moral, or cultural biases.

Biological Aggression

Aggression is a biological behavior exhibited, in several forms and with differing degrees of intensity, by all animal species. Any animal entirely lacking the ability to become aggressive would neither survive nor reproduce. In a broad study of aggression across animal taxa, Moyer (1976) has identified seven types of aggression: (1) predatory, (2) intermale, (3) fear-induced, (4) irritable, (5) territorial, (6) maternal, and (7) instrumental. Although this typology is useful for identifying the circumstances under which aggression often occurs, it should not be interpreted exclusively or categorically. Any given display of aggression, in other words, is a synthetic behavior that may combine several of these types into coordinated action. Predatory aggression is required for animals that prey on other animals. Intermale aggression is an essential aspect of competition for resources, including food, mates, and territory. Fear-induced aggression is required for defense against attack. Irritable aggression frequently is used to reinforce dominance and rank. Territorial aggression is displayed by both males and females and is directly linked to resource acquisition and defense. Maternal aggression is required for defense of offspring. Finally, instrumental aggression is goal oriented and forward looking—it has a future objective. Although several species display instrumental aggression, it is especially well developed in primates.

Great Ape Aggression

Because culture plays such a prominent role in human conflict and aggression, it can be difficult to ascertain the extent to which biological factors account for these behaviors. The confounding effects of human culture can, however, be controlled to a limited extent by examining conflict and aggression in nonhuman primates, and especially among the “great apes” who are most closely related to humans. Although the analogies are imperfect, the aggressive behaviors of our nearest phylogenetic relatives can provide important insights into the core of human conflict. Over the last few decades, primatological field studies have greatly increased our understanding of great ape behavior. A general conclusion arising from such research is that conflict and aggression among nonhuman primates is highly variable between species and heavily dependent on ecologies. Because human behavioral plasticity exceeds that of any other primate, it is reasonable to infer that intraspecific conflict and aggression is, for Homo sapiens, similarly variable and dependent.

Chimpanzees (Pan troglogdytes and Pan paniscus)

Of all the great apes, chimpanzees and humans are most closely related and last shared a common ancestor approximately 5 million years ago. Because chimpanzees are our nearest evolutionary relatives, scientific interest in their behavior has been intense, and chimpanzees have been intensively studied in both captive and natural environments. Although early studies of “common” chimpanzees (Pan troglodytes) failed to reveal exceptionally violent behavior, more recent research shows that chimpanzees are quite aggressive toward one another and engage in behaviors that, at least among humans, would be labeled “warlike.” Given their closeness to humans, violence among chimpanzees surprised no one, and it was commonly accepted that these two species were genetically and behaviorally alike. In recent years, however, primatologists have discovered that another species of chimpanzee, the bonobo (Pan paniscus), has remarkably different behavioral patterns, and that these differences are most pronounced in terms of conflict and aggression. Unlike common chimpanzees, bonobos are rarely aggressive toward one another and mortal conflict between them has yet to be observed.

Pan troglodytes, or common chimpanzees, are scrupulously territorial animals that live in male-dominated troops. As females reach maturity, they transfer from their natal group into neighboring ones. Males, who typically remain in the same troop their entire lives, continuously form coalitions as they strive for alpha status. This coveted status confers upon males various evolutionary benefits, including access to prime feeding grounds and females. High rank, however, is often tenuous and temporary. Males jockeying for dominance continuously form new coalitions, and dominance hierarchies are fluid. The formation and dissolution of these coalitions is the focus of Frans de Waal’s (2000) book Chimpanzee Politics: Power and Sex Among Apes. Despite the nearly constant tension between them, males within a single troop readily set aside their differences to defend—and even extend—their troop’s territory. With surprising regularity, males form “raiding” parties to patrol territorial boundaries. During such patrols, males will sometimes cross boundaries to attack and kill chimpanzees from neighboring troops. This aggressive behavior has drawn inevitable comparisons with humans, and it is the subject of Richard Wrangham and Dale Peterson’s (1996) book, Demonic Males: Apes and the Origins of Human Violence. Regardless of how one characterizes these behaviors, it is difficult not to conclude that chimpanzee and human aggression are similar in kind and intensity.

Not all chimpanzees, however, act in such distressingly familiar ways. Conflict between bonobos (Pan paniscus) is relatively rare, and aggression limited. Unlike common chimpanzees, bonobos live in a society that is female dominated, and newly mature males transfer to neighboring troops. Dominance is established by relatively stable matrilines. Males do not form coalitions for purposes of rank. Instead, males attempt to ingratiate themselves with high-status females. Male competition is minimal due to the fact that sex among bonobos is constant, open, and prolific. Bonobos routinely greet one another sexually, and use sex to defuse tension and maintain cohesion. Sex is not limited to male-female copulation (though this is certainly common), but also includes frequent female-female genital stimulation. When neighboring bonobo troops meet at territorial borders, there may be unease but there is little to no fighting. Indeed, the groups will occasionally and temporarily mix. Though conflict certainly exists among bonobos, it is modulated and rarely results in physical confrontations.

Although much research remains to be done regarding the extraordinary behavioral differences between common chimpanzees and bonobos, two factors appear to account for them: resource availability and mating opportunities. Common chimpanzees live in a much broader range of habitats than bonobos, and many of these ranges are limited or seasonal in resources. Bonobos, for their part, are geographically isolated and live in a small range of rainforest that is rich and regular in food resources. These differences in resource availability seem to be driving two remarkably divergent types of behavior. When resources are limited, conflict inevitably ensues. When resources are abundant, conflict is minimal. Resource availability thus sets the stage for differences in mating behaviors that impact the evolutionary imperative of reproduction.

Because territory is critically important in resource-constrained settings, male common chimpanzees advance their interests by forming strong coalitions that are able to defend and extend home ranges. This, in turn, provides males with access to females and their young, who are dependent on an adequate resource base for survival. But when resources are abundant, the dynamic is considerably altered. With adequate resources, the importance of territories—and males—diminishes. Females become free to pursue their evolutionary interests, which do not generally include high levels of conflict and aggression. Under the relatively rare circumstance of resource abundance, males become essential only for sexual reproduction. The result, as we see with bonobos, is a female-dominated, tranquil society characterized by frequent and open sexual behavior.

Gorillas (Gorilla) and Orangutans (Pongo)

After chimpanzees, gorillas are the nearest evolutionary relatives to humans, having separated from the hominid lineage around 8 million years ago. Unlike humans, but like our ancestors the australopithecines, gorillas exhibit a high degree of sexual dimorphism, a trait associated with dominance by a single alpha male and haremlike social structures. Gorilla troops typically number between 5 and 30 members. A single dominant male, known as a silverback, leads the troop and is the only reproductive male. Conflict within the troop is rare, and aggression is kept to a minimum by the silverback. Many field researchers have been struck by the apparent peacefulness of gorillas. As young males within a troop near maturity, the dominant silverback will force them to leave. After dispersing, young males roam alone or in small groups for a period of 2 to 5 years. When they have reached full size and maturity, these males begin seeking troops of their own. The primary source of conflict among gorillas occurs when silverbacks challenge one another for troop supremacy. Although the rewards are great, in terms of reproductive opportunities, the risks are significant for participants and others. Aside from the grievous injuries males may inflict on one another during such contests, victorious challengers may promptly kill any infants sired by the deposed silverback. Such killings cause mature females to resume estrus, and allow the new male to begin propagating his own genetic lineage in relatively short order.

Of all the great apes, orangutans—who last shared a common ancestor with humans approximately 14 million years ago—are the least social, a fact probably linked to habitat and feeding ecology. Though orangutans live in verdant rainforests on the islands of Borneo and Sumatra, food resources are often scarce. Orangutans are dietary specialists largely dependent on ripe fruits. Because such fruits are both sparse and seasonal, orangutan density is limited and sociality constrained. This fact alone may account for reduced conflict between them. Female orangutans and immature males do not establish territories, and they usually avoid one another as they forage across the territories of mature males. Mature males, for their part, are highly aggressive toward one another, and their territorial conflicts can be intense, even if infrequent. In a remarkable display of phenotypic plasticity, reproductively mature males who lack territories do not develop the large fatty deposits, or flanges, and long hair characteristic of territorial males. Because flanged males apparently fail to perceive nonflanged males as competitors, territorial males generally ignore them. This, in turn, allows ostensibly non-mature males to avoid conflict and roam across territorial boundaries in search of food and females. When nonflanged males encounter females, they are known to force copulation. This aggressive behavior finds its parallel in human rape. By nearly all accounts, female orangutans prefer copulation with flanged, territorial males who mate by invitation rather than force.

Although this brief survey of aggressive behavior and conflict among the great apes cannot possibly capture the full and subtle array of such behaviors, it provides basic insights into the wellsprings of that behavior. Evolutionary fitness ultimately is determined by differential survival and reproduction. Successful organisms are those that survive long enough to reproduce. Dominance and rank usually determine which individuals have access to the resources necessary for survival and the mates required for reproduction. Given these biological facts, it should come as no surprise that animals— humans prominently included—aggressively pursue these goals, and conflict is often the result.

Group Aggression

Like other animals, all humans are born with the behavioral capacity to be aggressive. This capacity, however, varies considerably depending on contexts and cultures. There also is variation in aggressive propensities between individuals. Certain people are more aggressive than others, and these differences may provide those individuals with a fitness advantage in some situations. In social settings, however, excess aggression can be costly, in terms of both energy and reciprocity. As is true of all adaptations, costs are weighted against benefits. Among highly intelligent social animals, this calculus is not as simple as it might seem. The biggest, strongest, and most aggressive—those most prone to conflict with others—do not always prevail. Studies of chimpanzees and baboons—both of whom live in troops similar in size to those of most known hunter-gatherer groups—consistently show that high rank is the balanced result of many factors, including inheritance, cooperation, intelligence, and aggression. Within-group aggression is limited—though never absent—by this combination of factors. Without-group aggression, however, implicates a different kind of calculus.

Out-group aggression can be either interspecific (across species) or intraspecific (within species), and sometimes both. Interspecific group aggression is frequently observed between species that occupy similar ecological niches, with the most prominent example being that of lions and hyenas. These sympatric and social species routinely attack one another in coordinated groups, and the results are often fatal. Because lions and hyenas directly compete for the same limited resources, conflict between them is nearly constant. Although postagricultural humans do not have many direct competitors, a few species have been perceived as such, with wolves being a primary example. Throughout history, humans have waged war on wolves, with the result being the near extinction of that species in many areas. Nonetheless, interspecific aggression involving humans and other species is relatively rare. The same cannot be said of intraspecific aggression involving humans. Human-on-human aggression is most intense and prevalent when it involves opposing groups.

On a general level, group living is a behavioral adaptation that confers significant benefits on social species. Among these benefits are cooperative foraging, predator avoidance, collective defense, offspring assistance, food sharing, and reproductive opportunities. Given these advantages, maintaining group cohesion becomes an important and perhaps even paramount goal. When groups splinter or individuals are expelled, the costs may be high. Smaller groups are less able to compete with larger ones, and social solitaires often do not survive. These costs intrinsically limit the amount of competition and conflict within a social group. Because group solidarity is critical to survival, cohesive behaviors have been favored by natural selection. Essential to these behaviors is the ability to distinguish group members from nongroup members and to treat them differentially. Primates, in particular, have well-developed abilities for recognizing outsiders. When survival depends on group solidarity, the differential treatment of in- and out-group members is adaptive. But when survival no longer depends on strict maintenance of boundaries between groups, such behaviors may become maladaptive.

Cultural Conflict and Aggression

Although it is difficult to reconstruct the precise social structures of early humans, it seems probable that Homo erectus lived in groups similar in size and nature to those of common chimpanzees. Whether characterized as a troop or a band, this type of social unit persisted for nearly 2 million years and played a key role in human evolution. At some point, these groups would become recognizable to us as band-sized hunter-gatherers. Despite this more modern characterization, these foraging bands continued to resemble common chimpanzee troops in overall size and structure.

While many bands were affiliated with one another through kinship or marriage and occasionally aggregated into something like tribes, these units eventually enlarged into chiefdoms, cities, and states. In all cases, this process involved a movement to centralized authority and social stratification. To consolidate power and govern, ruling elites began controlling cultural institutions and generating cultural products. These institutions and products were both material (public works, temples, palaces, art) and immaterial (knowledge, religion, ideology, nationalism). Regardless of form, many of these cultural forces played directly into the strong evolutionary behaviors associated with in- and out-groups. The creation of separate and distinct identities—setting one group apart from another— has long been the occupation of elites, who manipulate these identities to channel aggression and direct conflict. In the setting of cities, states, and empires, our ancestral hostility toward group outsiders—or the “other”—has proven costly, and it is in most modern contexts maladaptive. This emphasis on groups, however, does not imply that individuals are unimportant or that they passively imbibe something called “culture.”

Individual Acculturation and Aggression

At its core, culture is learning passed from generation to generation through social behaviors. By this definition, humans are not alone in having culture—many species teach their offspring behaviors essential for survival and reproduction. Despite this fact, human culture is qualitatively and quantitatively different from that of all other species. It has been said, with good reason, that the primary evolutionary adaptation for humans is culture. Culture does not, however, operate on a blank slate. In the absence of some defect, humans are born with certain capacities and limitations. These capacities and limitations are biological in nature and are sometimes explained by anthropologists using the biogram concept. The biogram represents a human at birth— an individual who has not yet been imprinted with learning or culture of any kind. Immediately after birth, cultural patterning begins and continues for the remainder of one’s life. This biocultural model is depicted in Figure 79.1.

Starting with an infant, the heuristic in Figure 79.1 tracks different phases of development and acculturation. Each outer circle represents a layer of social learning imprinted on the individual biogram. These acculturating layers are not rigidly fixed, neatly separated, or always applicable. The innermost rings are, however, fairly consistent across space and time: The first things infants learn are socialization and language. From the moment of birth, a child is embedded in social and linguistic settings. By the time children are able to interact and speak in social settings, the patterning process is already far advanced.

This process is both formal and informal, active and passive. It occurs by instruction, example, observation, and interaction. In nearly all cultures, this formative period also includes teaching and, in most societies, prominently features religion. A bit later, children begin absorbing cultural knowledge regarding society, history, vocation, and health. As children continue the long process of maturation, most receive additional instruction, with varying degrees of emphasis and intensity, in the following cultural topics: politics, economy, reproduction, sports, military, science, technology, literature, music, arts, dance, games, hobbies, and fashion. In developed countries, media play a key role in acculturation.

It is important to note that every individual participates differently and unevenly in culture and that the acculturating layers represented by this model are permeable, multidirectional, and variable. Layers can be added or deleted, depending on what is omitted, accepted, or rejected through the lifelong process of social learning. It is equally important to note that this process is never disinterested— someone or some group is always producing cultural knowledge and materials.

With these concepts in mind, it becomes easy to see that culture strongly patterns both aggression and conflict. Much of this patterning is a mere happenstance of birth at a particular time and in a particular place. Although these acculturating forces do not precisely determine how any given individual will act, they are powerful predictors of such action. When families, religions, societies, and governments take a keen interest in patterning individuals in a particular way, people usually think and act in accord with that acculturation. Through this process, essential evolutionary behaviors such as aggression and conflict can be either amplified or modulated. A good example of amplification is the militarist acculturation of children in ancient Sparta. A converse example of modulation is the pacifist acculturation of Semai children in Malaysia. In each case, interested adults and societies raise children in environments that place great emphasis on aggression (Sparta) or nonaggression (Semai), with fairly predictable results in terms of propensity for aggression and penchant for conflict. Most people are not, however, raised in cultural milieus so dedicated to these antipodal positions. For them, acculturating influences on aggression and conflict are less obvious, though no less influential.

Power, Population, and Resources

Though the drive for power is often obscured by the workings of culture, it is a fundamental, evolutionary impulse nearly always directed toward the acquisition of resources. In the late 1800s, Friedrich Nietzsche was the first to recognize this relationship and link power to evolutionary ideas regarding dominance. Nietzsche noted that all interactions between humans implicate power because, as social animals, we habitually order ourselves according to rank. This ordering creates hierarchies, and those on top have access to more resources than those on the bottom. As Michel Foucault later recognized, these relationships and imbalances do not involve only those of high and low rank—they envelop everyone in the social and cultural system. And as these systems become ever larger and more complex, power relationships become more subtle and pervasive.

This is a process that materialist thinkers have long understood, even if their analysis begins with economy rather than biology. For Karl Marx, all things cultural arise from and are tied to underlying material factors. Economic modes of production determine cultural forms, whether political, religious, legal, or moral. Historical progressions are an important aspect of this understanding. By materialist reasoning, hunter-gatherers have a mode of economy that structures their cultural forms. Similarly, feudalism produces one type of culture, and capitalism another. Cultural forms may vary, but only within the constraints of economy. By making economy foundational to culture, materialists simply recognize that all economies are constrained by resources, and ultimately by populations.

For nearly 2 million years, humans foraged for a living. Because naturally occurring plants and animals are everywhere and always limited, population sizes remained relatively small. Hunter-gatherer groups that became too large eventually depleted their resources and were faced with a stark decision—leave or starve. As long as there were unoccupied territories with untapped resources, migration could occur without conflict. However, migration into already occupied areas most often came at the price of conflict. Groups living in those areas would not have welcomed outsiders and usually resisted incursions by groups not closely related by kinship. It is not surprising, therefore, that archaeologists have discovered evidence of conflict among most preagricultural societies, and that among historical hunter-gatherer groups, conflict was a fairly regular occurrence. In most instances, this conflict revolved around resources.

Approximately 12,000 years ago, humans began domesticating plants and animals. Other than evolution itself, no other event has so profoundly influenced human history and culture. The shift from food gathering to food production led to permanent settlements and population growth. When the process of domestication began around 10,000 BCE, there were perhaps no more than five million people worldwide. Ten thousand years later (1 CE) and as a direct result of agriculture, global population had increased to 300 million. This explosive growth had many consequences, not the least of which is that hunter-gatherers were pressed on all sides by expanding agricultural communities. In some cases, this expansion would have occurred through assimilation. In others, it would have been violent. Though foragers had a long history of fighting one another over fertile lands, the conflicts they now faced were different. With their ability to produce food surpluses, agricultural communities were populous and specialized. Some of these specialists devoted themselves solely to the arts of war. Foraging warriors were no match for agricultural armies. This inexorable accretion ultimately resulted in the formation of chiefdoms, cities, states, and empires.

Although this sequential description is overly simplified and there were important variations, it roughly describes the transition from band-size groups to empire-size states. In a mere 10,000 years, humans had gone from living in groups numbering not more than 150 to groups numbering in the hundreds of thousands and even millions. Marvin Harris (1977) describes this process as one of constant intensification; once it started, it could not be stopped. Intensification has a logic and inertia of its own, and social groupings can only become larger and larger. Growing populations demand more resources. To meet these demands, production is improved and territories are expanded. Improvements in production and expansion of territories generate more resources, which are in turn consumed by growing populations. At this point, the cycle begins anew. Admittedly, this is a rather dry and mechanical description of postagricultural human history. It has the virtue, however, of identifying the resource-based cause of much conflict and aggression over the past 10,000 years.

None of this is to deny that aggression can be highly individualized, and that in isolated cases, those in power have pathological tendencies which may result in larger scale conflict. Only infrequently, however, do individual pathologies translate into war. When it comes to mass conflict, it is the people—those who produce and fight—who must be persuaded. Blatant appeals to conquest and spoils have not, except in rare cases (i.e., the Vikings and Mongols), proven effective in mobilizing entire populations for war. The material costs and mortal risks of conflict simply are too great. Knowing this, rulers and elites persuade and delude the masses with politics, ideology, religion, ethnicity, and nationalism. With depressing regularity, these identity-forging cultural forces have proven effective at tapping into ancestral and primatelike behaviors that favor, at all costs, one’s own group over another. Maintaining group separation and solidarity is key to this persuasion. So long as others remain strange and outside the group, aggression toward them is encouraged and justified. It is only when others are familiar and inside the group that aggression is discouraged and prohibited.

Future Directions

Aggression is an essential animal behavior that has evolved through natural selection over millions of years. In evolutionary terms, success (or fitness) is a matter of survival and reproduction. An animal entirely lacking in the capacity for aggression would not long survive and almost certainly would not reproduce. Certain animals are naturally more aggressive than others, and these differences usually relate to feeding ecology. Predators are sensibly more aggressive than browsers. Like other primates, humans are born with the capacity for aggression. At a biological level, this capacity does not differ in degree, kind, or intensity from that of other primates. Any primate— including humans—can become aggressive under various conditions or circumstances. Limited resources of all kinds (food, water, territory, mates) guarantee competition, and where there is competition, there will be aggression.

Where humans differ from other primates, and indeed from all other species, is in their capacity for extreme aggression and continuous conflict. Humans also differ from other primates and species in the extreme development of their cultural adaptations. It is this variable—culture— that accounts for hypertrophied human aggression and conflict. Culture can operate either to dampen aggressive impulses or to amplify them. For the better part of human history, culture has unfortunately been used to amplify those impulses, primarily through the promotion of distinct identities and separate groups. When culture co-opts naturally adaptive behaviors such as aggression, the results can be disastrous. Culture has the capacity to detach aggression from the pursuit of food, protection of offspring, and defense of territory. It also has the capacity to engender and redirect aggression toward others, with an intensity and scale unique in the animal kingdom. No other species cultivates aggression and encourages conflict with the same dedication or intensity as humans.

Because the capacity for aggression is neither mysterious nor deviant, and because conflict can nearly always be explained in terms of power and resources, there is not much to be gained from additional studies explaining what is already known. Although the proximate causes of conflict—such as people involved, issues invoked, and reasons provided—will continuously change with the progression of time, the ultimate evolutionary causes remain the same. So long as these causes are obscured and distorted by acculturating forces—whether in the form of nationalism, religion, ethnicity, or ideology—prospects for change are minimal. As is true of any behavior or description of behavior, aggression and conflict have their opposites. To understand aggression and what provokes it, future research should be directed at converse behaviors such as cooperation. The same is true for conflict. Without a thorough understanding of the conditions and circumstances under which aggression is minimal and conflict absent, our understanding of these subjects will remain incomplete.