The Primate Diaries

The Primate Diaries

Notes on science, politics, and history from a primate in the human zoo.

Freedom to Riot: On the Evolution of Collective Violence


From London to the Middle East riots have shaken political stability. Are the answers to be found in human nature?

"Anarchy" by Nathaniel Gold

     "Anarchy" by Nathaniel Gold

Police cars were overturned and shops looted as the mob descended on the city's central square. Rioters tore the police station’s outer door off its hinges and “used it as a battering ram" to break inside. Others smashed their way into the city building where they assaulted government workers, shattered windows, and destroyed furniture.

The portrait of a powerful leader was pulled from the wall and sent dangling from a balcony as angry voices below cursed him and the other "fascists" believed responsible for their condition. One man, a lathe operator who had gone on strike, ran onto the balcony holding up two plates loaded with cheese and sausage. “Look and see what they eat," he shouted to the crowd below, "yet we cannot get such food!”

The Novocherkassk riot on June 2, 1962, was Soviet Russia’s largest public uprising to date. More than two thousand took to the streets in response to the Communist Party’s decision to increase food prices by 30 percent at the same time that wages were being reduced. Workers walked out on the job, students left their classrooms, and men and women of all ages joined the chorus of protest. The crowd marched peacefully through lines of soldiers backed by armored vehicles that had been hastily assembled and went to voice their grievances directly with a communist government that claimed to be on the side of the worker.

But when authorities inadvertently fired on unarmed civilians the “noisy, aggressive, and far less reasonable members determined its focus and direction,” wrote historian Vladimir Kozlov in his book Mass Uprisings in the USSR (M.E. Sharpe Inc, 2002). Drunken fights and petty theft occurred alongside the anger over poverty and police brutality. From a crowd made up of individuals, each possessing the ability to make a free choice, something more powerful had been unleashed in which normal rules of conduct seemed not to apply.

"For some reason some kind of force filled me," testified one of the rioters during his trial. "Until this day, I do not understand how I got into this. What kind of devil was it that asked me to go and forced me to enter into the police department?"

Collective violence, extending from riots to warfare, presents a challenge to our ordinary understanding of free will. Actions that would rarely be taken by an individual on their own seem to be embraced when supported by a larger group. This can occur in societies ranging from the communist regime of Soviet Russia to the capitalist free market of modern day England. Given this commonality, perhaps the collective violence of a riot can be best understood as a biological event in which evolved cognitive responses encounter a unique environmental threat. And if that is the case, do individuals caught up in such incidents have any choice in the matter?

The Evolution of Mob Mentality

“Imagine you’re on a bus,” explains Vaughan Bell, clinical research psychologist at King’s College London. “It’s full of people and you have to jam into an uncomfortable seat at the back.” Very little connects you with any of the other passengers and it is unlikely you would even give them a second thought.

Suddenly, multiple windows are smashed open and you discover that the bus is under attack by a group of thugs who are trying to steal people’s bags through the broken windows. You very quickly feel a common bond with the other passengers and willingly cooperate with them to help fend off the thieves. Extreme circumstances have pushed you into identifying with the group against a common enemy.

“You didn’t lose your identity,” says Bell, “you gained a new one in reaction to a threat.” As Bell points out in the case of riots, that threat is often excessive force from the police that turns a disgruntled crowd into an angry mob.

This scenario is what psychologists refer to as the Elaborated Social Identity Model of crowd behaviour. Each individual remains a rational actor, but has been primed by natural selection to identify with the group during a period of crisis. This well developed ingroup/outgroup bias is what has allowed our species to be the most cooperative of the primates, but certain conditions have the potential to turn us against our own community. While the psychology of collective behavior may explain why individuals join together once a riot is under way, it doesn’t explain why the riot would begin in the first place. As it turns out, our primate cousins offer a unique insight into this question. Nonhuman primates offer a window into the range of behaviors available to our evolutionary ancestors and the legacy that they have passed down to us.

"Collective violence," wrote Harvard primatologist Richard Wrangham in the Annals of the New York Academy of Sciences, shows "a common human pattern evident in societies lacking effective central authority, manifested in ethnic riots, blood feuds, lethal raiding, and warfare." Such aggression, he says, is directly related to that of nonhuman primates and demonstrates a common evolutionary history. As Wrangham earlier wrote in his book Demonic Males: Apes and the Origins of Human Violence, our primate origins "preceded and paved the way for human war, making modern humans the dazed survivors of a continuous, 5-million-year habit of lethal aggression."

Wrangham is but the latest in a long history of evolutionary scientists to argue that collective violence is an adaptive feature of the human species. However, one of the earliest case studies to reach this same conclusion is actually, in the light of hindsight, a prime example arguing against this contention. By doing so, it offers a unique perspective into the factors that motivate collective violence in human societies and may even offer some clues about how to prevent it.

Anatomy of a Massacre

On October 27, 1930 a brief report in Time magazine described an attack that took place among a captive colony of 140 “Abyssinian” baboons that had been newly installed at Monkey Hill in the London Zoo. This was merely the latest outbreak in what would eventually be described as a massacre of more than two-thirds of the population.

According to the article, the attacks occurred when a young social outcast had “stolen a female belonging to the king." He fled with his captive behind a hastily built barricade where an indignant crowd gathered and trapped the two inside. After “two days of siege” he attempted to escape from his sanctuary only to be brutally attacked and killed by the waiting mob. Each attack led to a counterattack by a rival alliance. After several years the death toll amounted to ninety-four individuals in all--two-thirds of them male. Among the deceased were fourteen infants, most of them strangled either by male attackers or by their own mothers.

What transpired on that barren landscape was carefully documented at the time by Solly Zuckerman (later Lord Zuckerman), a recent émigré who had just completed his doctorate in anatomy at the University of Cape Town in South Africa. Faced with such senseless brutality inflicted by one group member against another, Zuckerman speculated on what could have stirred the hostilities and then kept them going for so long. He eventually concluded that the cause was “social discord.” The death of one individual upset the political hierarchy, and violence ensued until stability was regained.

The massacre of Monkey Hill has since become a classic zoological case study revealing the danger of embracing a faulty assumption about “natural” behavior [see my interview with primatologist Frans de Waal for more on this topic]. Zuckerman assumed he was observing evolution in action and that natural laws had shaped these beasts to engage in lethal aggression. Like most biologists of the time, he accepted the view that primate social behavior followed a one-size-fits-all model that was unaffected by environmental factors. While human beings learn to rise above their bestial nature, animals are, well, simply animals. Or so the argument went.

“Behaviour is uniform,” wrote Zuckerman in The Social Life of Monkeys and Apes, published in 1932. “The common belief that the new environment [of captivity] grossly distorts the expression of these relationships has no foundation in fact. The pattern of socio-sexual adjustments in captive colonies is identical with that observed among wild animals.”

He couldn’t have been more wrong. A few decades later ethologist Hans Kummer confirmed this by comparing the behavior of captive baboons in Zurich with wild populations in Ethiopia. What Kummer found was that captive baboons showed many more aggressive acts than their free-ranging counterparts (nine times more for females and seventeen and a half times more for males). The massacre of Monkey Hill therefore represents a kind of controlled experiment on the potential dangers of social engineering, one that demonstrates the lethal consequences of flawed assumptions.

It is true that Abyssinian baboons, now more commonly referred to as Hamadryas after their scientific designation Papio hamadryas, are notorious for their aggressive behavior. But the levels of aggression that Zuckerman described have never been observed in the wild, not then or since. Zuckerman assumed that captive conditions had no effect on baboon society and so didn’t think it was relevant that more than one hundred individuals were enclosed in a facility that measured only 100 feet long by 60 feet wide. It never occurred to him that the social discord he observed had been manufactured, and that he was the cause. The inhumane treatment that left nearly 100 baboons dead was the ultimate, and tragic, result.

From Colony to Metropolis

Since the events of Monkey Hill, hundreds of studies with captive primates have shown that impoverished environments result in heightened aggression and antisocial behavior. Such behavior has been shown to significantly increase under conditions of overcrowding, when there’s a lack of novelty in food, entertainment, or social opportunities, when the population increases and the number of strangers in a colony grows, or, most crucially, when food is limited and/or fluctuates dramatically (see Honess and Marin, 2006 for a review of the literature). Any of these factors can greatly increase the level of stress that individuals experience and promote social discord.

As neuroscientist Robert Sapolsky has documented in multiple studies, social stress and aggressive responses are highly correlated. When these stressors are too great it can cause what would be an otherwise adaptive response to become exaggerated [see my post Stressing Motherhood: How Biology and Social Inequality Foster Maternal Infanticide for a detailed discussion of this process]. Often all it takes is the right conditions to trigger a violent response. But if multiple factors are present and persist it can result in sustained aggression or even colony collapse. In this way, stress-induced aggressive behavior is both adaptive and the result of environmental conditions; a response that can be exaggerated or distorted when living in captivity.

It should come as no surprise that one of the most important environmental factors involved in stress-induced aggression is food. Another classic, if somewhat cruel, study by Charles Southwick in 1967 found that increasing the amount of food in a captive colony of rhesus macaques by 25 percent decreased the amount of aggression by 50 percent. However, when a normal amount of food was restricted (by placing it in a single basket where it could be monopolized by a few high-ranking individuals) the level of overall aggression tripled and the number of violent attacks per hour was five times greater.

"The animals are especially quarrelsome and competitive when the food supply is restricted," Southwick concluded dryly. But he added that "the increased tension and aggressivity of captive animals exaggerates certain types of phenomena, and hence the results must be interpreted in proper perspective with reference to natural situations."

What was clear was that when all colony members had enough to eat aggression was cut in half. But when inequalities were introduced, so that only a few individuals enjoyed an excess while the majority went without, it was met with a violent response. These findings were subsequently confirmed and now form the basis for food policy in captive primate facilities around the world. Captive conditions are now understood to significantly alter animal behavior unless precautions are taken to both understand species-typical behavior under natural conditions and provide an environment that allows its expression. Can the same be said about human societies?

Food Riots in England

Figure 1. Major outbreaks of rioting in England (red lines) correlate with average price of wheat between 1780 and 1822. Figure by author using data from Archer (2000). Click image to enlarge.

In our own species, historical and sociological studies of factors contributing to collective violence have found some striking parallels with studies of captive nonhuman primates. For example, John Archer in his book Social Unrest and Popular Protest in England showed that major outbreaks of rioting between 1780 and 1822 correlated with high wheat prices (see Figure 1 above). In nearly all cases the riots were preceded by a sharp rise in price and once the price fell the incidence of riots fell with it. This isn't to suggest that wheat price alone was the cause, or that a rise in price always resulted in a riot. But it does suggest that the two were correlated and that a rise in food price promoted the same kind of social discord that lay behind incidents of collective violence.

Identical findings were reported in a study by Marco Lagi, Karla Z. Bertrand and Yaneer Bar-Yam of the New England Complex Systems Institute in Cambridge, Mass. In their report, published August 11, the authors detail the close correlation between global food prices and the incidence of riots in North Africa and the Middle East (see Figure 2 below). In 2008 more than 60 riots occurred worldwide in 30 different countries during a peak in food prices. After declining temporarily in 2009, even higher prices at the end of 2010 and the beginning of 2011 coincided with additional food riots as well as the larger protests and revolts that have become popularly known as the Arab Spring. In contrast, there were relatively few incidents of collective violence when food prices were low.

Food Price Index and Riots

Figure 2. FAO Food Price Index from January 2004 to May 2011 and the beginning dates of "food riots" and protests (red lines). Reproduced from Lagi et al. (2011). Click image to enlarge.

"The timing of peaks in global food prices and social unrest implies that the 2011 unrest was precipitated by a food crisis that is threatening the security of vulnerable populations," conclude the authors. "Deterioration in food security led to conditions in which random events trigger widespread violence."

These findings may also help to explain the timing of riots in England the week before this paper was published. As Bar-Yam and colleagues point out, while the uprisings in their study were associated with dictatorial regimes, rising food prices are likely to affect impoverished communities in otherwise wealthy nations as well.

"The price of bread has more than doubled in the past five years in England," Bar-Yam explained via e-mail. "As in other parts of the world, London has a population of poor individuals vulnerable to food prices who are likely to engage in protests and participate in social disorder under these conditions."

Ironically, it may have been the very policies promoted by England and other Western governments that lay behind these conditions. One of the main causes of the spikes in global food price, according to Bar-Yam and colleagues, was investor speculation that resulted in an economic bubble like the one that hit the housing market in 2008. Beginning in 2001, financial institutions like Goldman Sachs and Morgan Stanley in the United States as well as Barclays Capital in the UK successfully lobbied their respective governments to deregulate the commodities market. This allowed them to invent new financial products, known as derivatives, that caused an explosion of speculation and volatility in agricultural prices. According to data from the United Nations, this investment rose from $13 billion in 2003 to $317 billion by 2008. The price of food rose along with the value of these investments, creating a financial bubble that put increasing strain on those communities already on the edge.

England's Conservative government also implemented austerity measures at the same time as the peak in food prices that rolled back many social programs that poor communities relied on. On November 10, 2010, for example, student protesters rioted when cuts to education caused tuition fees to nearly triple. Likewise, additional cuts targeted youth and community centers, medical coverage, unemployment and disability payments, child benefits, as well as housing and fuel subsidies for pensioners. England already had one of the most unequal societies in Europe based on the divide between rich and poor. Such austerity measures may have pushed this division to its breaking point.

An interactive map created by the Centre for Advanced Spatial Analysis at University College London makes clear that the riot outbreaks were clustered in the most economically deprived regions of the city. It was these regions that would have been most aversely affected by the austerity measures and, with a peak in both food and energy prices occurring at the same time, the environmental conditions were ideal for a triggering event that would push an already stressed population over into social discord.

This conclusion is further supported by an analysis of similar austerity measures throughout Europe during the 20th century conducted by economists Jacopo Ponticelli and Hans-Joachim Voth of the Centre for Economic Policy Research in London. According to their report Austerity and Anarchy: Budget Cuts and Social Unrest in Europe published in August, there was a "clear link between the magnitude of expenditure cutbacks and increases in social unrest."

As Ponticelli and Voth point out, when expenditure cuts reached 1 percent or more of the nation's Gross Domestic Product, the total number of demonstrations, riots, assassinations, and general strikes in a single year would increase by one-third compared to periods of budget expansion. When budget cuts reached 5 percent of GDP the number of incidents doubled (see Figure 3 below). According to London's Financial Times, England's current budget cuts are 4.5 percent of GDP.

Expenditure cuts in Europe

Total amount of social discord (CHAOS) in Europe between 1919 and 2009 correlates with the value of budget cuts relative to GDP. Reproduced from Ponticelli and Voth (2011). Click image to enlarge.

It was in the midst of these environmental conditions that police fatally shot Mark Duggan on August 4th and allegedly beat a 16-year-old girl during what was reportedly an otherwise peaceful protest in response to the shooting.

"This was the triggering event," says Bar-Yam, "that led to spontaneous wider violence." After five days of rage the damage was estimated to be £200 million ($326 million) and resulted in the arrest of more than 3,000 people. "It makes sense that in the beginning, the people involved were people in need. The violence then cascaded to others, who took advantage of the social disorder for other reasons. Social disorder is contagious."

As in London, the Novocherkassk riot forty years ago died down as those involved eventually dispersed, sobered up, or found themselves in jail. As the riot population declined, the shared social identity declined with it. But the rioters left behind a physical scar on the urban landscape, evidence of the rage shared by thousands of people during a time of acute environmental stress. However, while the collective violence may have waned, the political meaning of the events remained hotly contested. Soviet Premier Nikita Khrushchev announced that the Soviet rioters in 1962 were nothing more than “antisocial elements who spoil our lives” and condemned them all as “grabbers, loafers, and criminals.” British Prime Minister David Cameron would offer nearly identical words. Others, such as The Daily Telegraph's former editor-in-chief Sir Max Hastings, would portray the rioters as little different than Zuckerman's baboons from Monkey Hill, “wild beasts" who "respond only to the instinctive animal impulses.”

But what is to blame for such cases of collective violence--nature, or the unnatural conditions of modern life? While there may well be evolved responses that promote collective violence, research in captive primates suggest that these behaviors are heavily influenced by environmental stress. During the past year environmental conditions were just right for the triggering of social discord in our own society and, in the contagion that followed, violence quickly spread among a population predisposed to a shared identity.

For London and the cities throughout North Africa and the Middle East, it appears there was a free choice to riot after all. But the choice didn't come from the rioters alone, it rose from leaders and policymakers and the larger society as a whole. Riots reveal a colony in discord. Many of us have acknowledged the widening inequality and economic decline of our most impoverished citizens--but we chose to ignore it.

Aleksandr Solzhenitsyn, after experiencing firsthand the inequality and injustice that emerged from the Soviet command economy, wrote that the Novocherkassk riot was the first indication that the Iron Curtain was beginning to unravel.

"We can say without exaggeration," he wrote in The Gulag Archipelago, "that this was a turning point in the modern history of Russia." Free markets are theoretically designed to be flexible so that they rapidly respond to the needs of individuals and society. If this assumption is flawed we will need an alternative. Human nature is not destined for social discord so long as we have the freedom to choose conditions that can reduce the potential for collective violence. But the question remains if we will do so.

Selected References:

Marco Lagi, Karla Z. Bertrand, & Yaneer Bar-Yam (2011). The Food Crises and Political Instability in North Africa and the Middle East. New England Complex Systems Institute. arXiv: 1108.2455v1

Jacopo Ponticelli and Hans-Joachim Voth (2011). Austerity and Anarchy: Budget Cuts and Social Unrest in Europe, 1919-2009. Centre for Economic Policy Research Discussion Paper. VoxEU:

John Archer (2000). Social Unrest and Popular Protest in England, Cambridge University Press, p. 30.

Paul E. Honess and Carolina M. Marin (2006). Enrichment and aggression in primates. Neuroscience & Biobehavioral Reviews 30(3): 413-436. DOI: 10.1016/j.neubiorev.2005.05.002

Richard Wrangham and Michael Wilson (2004). Collective Violence: Comparisons between Youths and Chimpanzees. Annals of the New York Academy of Sciences 1036: 233–256. DOI: 10.1196/annals.1330.015

The views expressed are those of the author and are not necessarily those of Scientific American.

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