“We know that we are apes, but we cannot be classified simplistically as ‘naked apes’ or ‘killer apes’ or ‘moral apes.’…Our past is complicated; so is our present, and so will be our future.” – Paul Ehrlich (2000: 331)
“When we are bad, we are worse than any primate that I know. And when we are good, we are actually better and more altruistic than any primate that I know. ” – Frans de Waal
The Eagles headed back to their cabin feeling dejected after losing a tug-of-war contest to their rivals, the Rattlers. Along the way, one of the boys noticed the Rattlers had forgotten their flag on the baseball field, leaving it unprotected. Craig and Mason soon seized it, but struggled to tear it to pieces. McGraw then presented some matches and suggested they burn it instead. The group then hung the flag’s charred remains from the top of the backstop fence. Mason said, “You can tell those guys I did it. If they say anything I’ll fight ‘em.”
The above scene is from the psychologist Muzafer Sherif’s classic social psychology experiment at Robbers Cave, Oklahoma during the summer of 1954. Sherif divided twenty-two 11-year-old boys with comparable backgrounds into two even groups at nearby cabin sites, with the boys kept unaware of the other group’s existence.
After giving them a week to bond among themselves, Sherif introduced the groups to each other and announced that they would be competing for prizes in team sports and other events. Eventually the rivalry grew heated, and the boys turned to name-calling, flag-burning, and vandalizing each other’s cabins. The competition nearly escalated into serious violence, with sticks and rocks as potential weapons, before adults intervened.
Sherif’s experiment is sometimes cited as a depressing warning of how easily people can slide into “us versus them” hostilities, even if the groups are formed rather arbitrarily, and even if we’re only talking about preadolescent boys with little at stake except ego and trivial prizes. There is truth to that warning. People can cling tightly to group identities, sometimes resulting in serious animosity toward outsiders.
Rivalries that fall along national, ethnic, ideological, or religious divides have the potential to escalate into more severe vitriol, violence, and even war: Sunni–Shia, Muslim Seleka–Christian anti-Balaka, Israelis–Palestinians, Kyrgyz–Uzbeks, Hutu–Tutsi, Russians–Ukrainians, Americans–Afghans, etc. Certainly, rivalries are not the entire story of human group interactions, but they occur often enough that many have wondered whether group conflict is an inevitable part of human existence. Others have asked if the roots of intergroup conflict stem from the base of our evolutionary lineage as a species, or possibly even earlier.
These are difficult questions, partly because our past is often mythologized, where it is tempting to make sweeping generalizations that venture beyond the facts. One famous example includes Barack Obama’s Nobel Peace Prize acceptance speech when he said that: “War, in one form or another, appeared with the first man.” Winston Churchill thought similarly.
However, such claims are often based on an imagined past, not evidence, and reconstructing an accurate picture of our species’ prehistory is a notoriously difficult task. To do so, researchers usually round up some of the usual anthropological suspects by studying: (1) our primate cousins, to ascertain possible shared characteristics we may have inherited from a common ancestor; (2) living hunter-gatherer populations as an (imperfect) model of our more recent evolutionary past; (3) cross-cultural variation, to assess the full range of human behavior; and (4) most directly, the archaeological record.
By now, it is fairly well-known that chimpanzees, one of our genetically closest relatives (the other being the peaceable bonobo) engage in lethal violence within and between neighboring groups. In a paper published last September in Nature, Michael L. Wilson and twenty-nine fellow primatologists reported that across eighteen chimpanzee communities in east and west Africa, there had been 152 killings over 426 total years of field observations (Wilson et al 2014). Furthermore, killings were observed in fifteen of eighteen of the communities, including those with minimal human interference. Most victims (63%) were from different communities than the attackers, and the authors concluded that killing among chimpanzees was adaptive and a means of removing unrelated rivals when one group had superior numbers and the potential risks from engaging in an attack were low.
What to make of this? On one hand, we can see tantalizing parallels between chimpanzee and human intergroup violent behavior. For one, chimpanzee killings are overwhelmingly a male activity, as they comprise 92% of participants in attacks. Killings also occurred over a wide geographic range, from Senegal to Tanzania, and were therefore not merely an aberrational phenomenon specific to one community or the result of human impact.
On the other hand, lethal violence was rather infrequent, as the majority of communities had rates of less than 0.2 killings per year. In some communities lethal violence had never been observed. These rates are not easily translatable to human societies today simply because we live in much bigger groups, and a single chimpanzee victim will be much more impactful. Still, if lethal violence among chimpanzees is adaptive, it appears to be only sporadically so, not a regular feature of daily life. Lethal violence is also more likely to occur under specific circumstances. For example, Wilson et al. found that chimpanzees were more likely to kill when there were more males around, and when population densities were higher. As is the case in humans, chimpanzee behavior is flexible and responsive to social and ecological variables. They are no more automatons than we are.
Elsewhere, Wilson wrote that he was agnostic about what chimpanzee lethal violence means for us, adding that “definitive claims about human behavior need to be based on data from humans.” But the human data are also tricky. The historians Will and Ariel Durant once suggested that: “War is one of the constants of history…In the last 3,421 years of recorded history only 268 have seen no war” (1968: 81). That seems rather conclusive: war is a part of who we are. However, the Durants’ calculation does not mean that war was present everywhere on the planet simultaneously, and if we cast our net wide enough it makes sense that we would find conflict somewhere. Nor does it necessarily mean that war was common in pre-history.
Contemporary hunter-gatherer societies are often viewed as stand-ins for our prehistory. While anthropologists emphasize that all societies change over time, the rationale is that prior to agriculture, humans acquired food in this manner for the vast majority (>90%) of our species’ history. When the anthropologists Douglas Fry and Patrik Söderberg (2013) looked at violence in twenty-one contemporary and historical mobile hunter-gatherer groups, they found 148 lethal incidents in the ethnographic record dating back to the early 1800s, with a median of 4 incidents per group.
Their findings were not very consistent with the idea that war and intergroup aggression were a consistent feature of mobile hunter-gatherer groups. Only a minority of lethal incidents occurred between different societies. Instead, 36.3% of lethal incidents were within the same local group (relatives, spouses, other group members), 48.7% were within the same society but not the same local group, and 15.0% were between different societies (neighboring cultures, missionaries).
Additionally, most killings were dyadic, consisting of one aggressor and one victim (that is, homicide). These often had personal motives such as sexual jealousy or revenge, rather than stemming from impersonal intergroup hostilities. Only 22% of the incidents involved coalitionary violence, where more than one person participated in killing more than one person. Roughly half of the groups (10 of 21) had no coalitionary violence events, while three had no lethal events at all.
However, the most obvious and direct way to understand violence in our prehistoric past is through the archaeological record. There are clear examples of skeletal trauma indicating that interpersonal and group-level violence appeared in prehistory well before modern nation-states. Our ancestors were not complete peaceniks. Like us, they were complex.
But this is a far cry from saying that war has been unending since the beginning of humanity. In fact, violence seems to have been relatively rare before the increasing population densities and fixed settlements that accompanied agriculture. In a thorough review of prehistoric violence, the archaeologists Jonathan Haas and Matthew Piscatelli wrote, with emphasis, that:
“globally, at least 2,930 skeletal remains of Homo sapiens have been recovered at over 400 archaeological sites dating prior to 8000 BC/10000 BP… the small number of skeletal finds mentioned above showing ambiguous signs of conflict come from a comparatively small number of sites. Rather than demonstrating the commonness of ancient warfare among humans, consideration of the entire archaeological data set shows the opposite… The archaeological record is not silent on the presence of warfare in early human history. Indeed, this record shows that warfare was the rare exception prior to the Neolithic pressures of population densities and insufficient resources for growing populations” (2013: 182-3).
Prior to agriculture, there were several reasons that mobile hunter-gatherers would have little incentive to engage in warfare. These include small group sizes, an egalitarian social structure, kin and social ties to neighboring groups who were a source of mates and trade, low population densities that allowed easy mobility to new territory should tensions arise, and the relative lack of accumulated wealth that could be an incentive to attack one’s neighbors (see Fry and Söderberg 2013’s appendix for a fuller list).
So, were our ancestors naturally violent or peaceful? It doesn’t appear that war was ubiquitous in our hunter-gatherer ancestors. But perhaps a better answer to that question is “it depends.” As with chimpanzees, intergroup violence in humans likely ebbed and flowed situationally rather than being an inevitable outcome of human nature. Context matters, and any attempt to extrapolate clear trends of violence over human pre-history risks sacrificing nuance and understanding local variation. Along these lines, in a recent paper in the Yearbook of Physical Anthropology, the bioarchaeologists Debra Martin and Ryan Harrod write that patterns of violence via skeletal trauma “suggest variability, nuance and unevenness in the type, use, and meaning of violence across time and space and therefore defy generalizations or easy quantification” (in press).
Another reason the question is so difficult to answer is that humans are so behaviorally flexible, with a capacity not just for hate and conflict, but also for cooperation and love, even for non-kin and members outside of our group. Aggression and violence are part of our species’ behavioral repertoire, but at what frequency, and in what form, are more complex questions. We have the capacity to give someone the shirt off our back, and the kidney underneath it, but we can also pick up an automatic weapon and aim it at an ‘enemy’ or even participate in genocide. The challenge is not to figure out whether our species is inherently violent or altruistic, but why both extreme capacities are found within a single species, and what circumstances and social structures facilitate or impede those behaviors.
Finally, to return to the boys at Robbers Cave, the last stage of the experiment is at times forgotten. Sherif created situations that required the Rattlers and Eagles to put aside their differences in order to achieve “superordinate goals” that neither group could accomplish alone – pooling their money to pay for a movie (“Treasure Island”), fixing a damaged water tank that supplied both cabins, etc. By the end of camp, both groups agreed that they would travel home to Oklahoma City on the same bus. Sherif noted that the boys chose to sit intermingled, rather than strictly along group lines. On the trip home, they sang together (Oklahoma!), exchanged addresses, and at a refreshment stop the Rattlers volunteered to pay for malt drinks for both groups.
The lesson of Robbers Cave is not that the boys were biologically inclined to be vicious or virtuous. Rather, they were capable of moving in either direction. Same boys. Different circumstances. This makes sense. From an evolutionary point of view, flexibility is the very essence of behavior, as it allows organisms to respond to external conditions. After all, we can find violence in ‘peaceful’ bonobos, fruit-eating in alligators, and meat-eating in herbivorous orangutans. And perhaps one of our species greatest assets is our adaptability, to be flexible enough to live in a range of physical environments, consume a variety of diets, and respond to the other highly intelligent, behaviorally complex, humans around us. Sometimes we compete, sometimes we cooperate; we come equipped for both.
Durant W and Durant A. 1968. The Lessons of History. New York: Simon & Schuster.
Ehrlich PR. 2000. Human Natures: Genes, Cultures, and the Human Prospect. Shearwater Books.
Fry D, Söderberg P. 2013. Lethal aggression in mobile forager bands and implications for the origins of war. Science 341(6143): 270-273.
Haas J and Piscatelli M. 2013. The prehistory of warfare, In War, Peace, and Human Nature. Pp. 168-90 in: D Fry (ed.) Oxford University Press.
Martin DL, Harrod RP. In Press. Bioarchaeological Contributions to the Study of Violence. Yearbook of Physical Anthropology.
Wilson ML, Boesch C, Fruth B, Furuichi T, Gilby IC, Hashimoto C et al. 2014. Lethal aggression in Pan is better explained by adaptive strategies than human impacts. Nature 513(7518): 414-7.
[I originally wrote this essay for the website This View of Life in January.]