What Our Primate Relatives Say About War

Chimps fight viciously, but bonobos make love, not war. Why are we more like one than the other?

This leads us to the second qualification. A key reason why humans, bonobos and chimpanzees differ at all is the environment in which they evolved, and that environment’s selective pressures shaping the evolution of their social behavior. Here again, bonobos are the odd man out. Humans and chimpanzees have occupied diverse habitats across a very large range in the last several million years, stretching across the breadth of Africa and often comprising of patchy food resources that give rise to competition. In contrast, the ecology of the bonobos has been very different. Confined to a range below the Congo river in central Africa, bonobos occupied a more stable and benign habitat with dense, lowland forest and more evenly distributed and high-quality foliage, and the absence of competition from gorillas, all of which reduced between-species and within-species competition, especially among males. Accordingly, ecology makes bonobos a less representative model than chimpanzees for understanding human behavior.

Third, human behavior must be understood as a consequence of evolutionary history both long before and long after any common ancestor with primates. Let’s consider those older roots first. Humans share many traits that are common not just to primates, but to all mammals and even all vertebrates extending tens or hundreds of million of years into the past. For example, evolutionary older parts of the human brain elicit responses such as fear, aggression and the fight or flight response, which are shared among all mammals. Forget chimps or bonobos—much of human behavior can be understood as mammal-typical. But by the same logic many human traits are primate- or great ape-typical as well, making gorilla and orangutan behavior also important contexts for a full understanding of human behavior.

Now let us consider human evolution since our great ape common ancestor. Although, as argued above, much of human behavior carries the baggage of our distant evolutionary heritage, it has been fine tuned as the result of adaptations to the unique physical and social environment in which we—our species—evolved over the last 2 million years or so. Over and above whatever chimps or bonobos do, therefore, humans display adaptations to deal with problems that were uniquely ours. While there are many things unique to humans, perhaps the most significant has been collective action in large groups of non-kin, and defense and offense against rival groups. Inter-group conflict may be important among chimpanzees, but Homo sapiens turned it into an art. Although the details remain highly controversial, a series of new studies in archaeology and anthropology have debunked Rousseau’s myth of the peaceful savage. Death rates (as the percentage of adult males killed in intergroup conflict) among indigenous and prehistoric societies make the wars of the 20th century seem like skirmishes. Although humans were not always at war, human societies were always organized around its ever-present threat.

A sensitivity to human evolution and the behavior of chimpanzees and bonobos forces students of modern students of conflict to face two hard truths. First, we evolved in conditions of resource competition where fear of others, aggression and violence offered adaptive solutions to protect and provide for ourselves and our kin. We therefore need to amend Clausewitz. Humans do indeed wage war for political purposes, but long before war for raison d’etat there was war for resources. International politics is therefore not the root of war but merely an example of it—the continuation of seeking access to valuable resources by other means. Accordingly, when we consider “Why war?,” we have an answer: war is one of Mother Nature’s solutions to compete successfully for resources.

Second, the human traits of egoism, dominance, and in-group/out-group bias are at least partly adaptations to the ecological conditions prevalent in human evolution. It is not assumed that we simply inherited these wholesale from a common ancestor, or the common ancestor we share with the chimpanzee. Clearly, we have undergone many physiological and behavioral changes since then and ecology has been as or more important. But although humans and chimpanzees appear to have travelled much of the road to war together, we have gone far further. The particular socioecological setting in which humans evolved meant that aggression and war were significant behavioral adaptations. These same settings led to remarkable levels of cooperation as well, but note that this cooperation is selectively directed towards in-group members, the better to avoid exploitation by rival groups and organize for war. These adaptations, lamentably, remain with us today and influence our behavior, politics and society.

The true source of the tragedy of the human condition is that we evolved in conditions of intense resource competition. Like Russell Crowe organizing the outnumbered combatants in Gladiator, natural selection favored individuals who cooperated to avoid being killed—and, if necessary, to kill. Regrettably, Einstein's concise question, “Why war?”, is answered by nature equally succinctly: because we are human.

Dominic Johnson is Professor in the Department of Politics and International Relations, University of Oxford. Bradley A. Thayer is Professor and Head of the Department of Political Science, Utah State University.

Image: Wikimedia Commons.

Editor's Note: This piece was originally posted on January 29, 2013. We are recircualting it due to audience interest.