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What was once the largest known group of chimpanzees has descended into factional violence over the past decade, and primatologists think that humanity could learn something from their observations.
Nearly two dozen authors contributed to the paper, published last week in Science. The researchers tracked the Ngogo chimpanzee group over the course of 30 years in Kibale National Park, Uganda. During that time, they witnessed the group’s “fission,” an event they estimate to be a once-in-500-year occurrence.
Primates rely in part on mutual grooming to reinforce social bonds. There are observed limits to the size of a grooming network, depending on the particular species. However, larger groups of apes can cohabitate peacefully as long as there is some interchange between the component clusters.
What the researchers learned from watching the Ngogo group is that a breakdown in that interchange can quickly lead to polarization and geographical separation. Disturbingly, violence seems to be the endpoint of that process.
The researchers conclude by challenging the notion that human conflicts are really about political or religious ideology, as they often appear to be. Apes lack such abstract differences of opinion. And yet, the fate of the Ngogo group qualitatively resembles human phenomena like segregation, civil war, and even genocide.
“This study encourages a reevaluation of current models of human collective violence,” the researchers write. “If chimpanzee groups can polarize, split, and engage in lethal aggression without human-type cultural markers, then relational dynamics may play a larger causal role in human conflict than often assumed. Cultural traits remain essential for large-scale cooperation, but many conflicts may originate in the breakdown of interpersonal relationships rather than in entrenched ethnic or ideological divisions.”
The Tragic Unraveling of the Ngogo Group
The timeline of the Ngogo group’s fragmentation is well-detailed in the paper. However, the root causes remain more speculative.
When observations of the group first began, it consisted of about 118 individuals, growing to just over 200 before fragmentation. Throughout that time, there were either two or three identifiable grooming networks within the larger group. However, these networks were fluid. Roughly 29% of chimpanzees switched from one sub-group to another within any given year, and 44% of infants had parents belonging to different networks.
It appears that the cohesion of the larger group depended in part on that intermixing and in part on certain key individuals in the dominance hierarchy.
The researchers speculate that the death due to natural causes of some of those key individuals precipitated the split. There isn’t much evidence for that beyond timing, but shortly after the death of those six adults came the first clear sign that something was wrong.
In 2015, members of the Central and Western Ngogo groups came together. Ordinarily, this would lead to some mixing. Instead, the Central chimpanzees chased away the Western sub-group. Over the ensuing weeks, the groups began to distance themselves geographically from each other.
Almost immediately, reproductive patterns changed. Babies born after 2015 all had two parents from the same group. Each group began organizing patrols to keep the other out of its territory.
Two years later came the first instance of violence, in which Western chimpanzees severely injured a Central alpha. Interestingly, the victim had been a member of the Western grooming network as recently as 2014.
The violence escalated from there. By 2021, the Western chimpanzees were conducting a campaign of infanticide against the Central group, killing at least 14 babies in three years, and likely more.
Are Social ‘Technologies’ the Solution to Mass Violence?
This isn’t the first time scientists have suggested looking at ape behavior to understand human dynamics. Chimpanzees are, after all, our closest relatives.
Anthropologist Robin Dunbar published an influential and controversial paper in 1992, correlating the maximum size of observed grooming networks with primates’ brain size. There’s a certain cognitive load associated with keeping track of everyone who’s in a social network and how each of those individuals relates to all the others.
The idea is that hanging out with another ape and resolving conflicts over any extended period of time requires understanding how they fit into the group. And bigger brains allow apes to track more relationships and larger groups to remain stable.
For chimpanzees, Dunbar’s number — that is, the hypothetical maximum group size — is around 60, which coincides with the size of the Ngogo subgroups when observation began. By the time of fragmentation, there were more like 100 apes in each group.
The ‘Monkeysphere Hypothesis’
Applying Dunbar’s findings to the human brain leads to a number of around 150. That’s the controversial part of his findings: the implication that a person isn’t capable of having full empathy for more than about 150 others, beyond which everyone is a more abstract stranger. The author Jason Pargin — then going by the pseudonym David Wong — popularized this notion in 2007 as the editor of Cracked, coining the term “monkeysphere” to describe our personal social orbits.
Obviously, humans live in groups much larger than 150, with some modern cities now containing tens of millions of us. That’s not the only way in which humans have surpassed our natural limitations, however. The ability to develop technology is our superpower, permitting us to do all sorts of things that are otherwise impossible for an ape.
Typically, we associate the word “technology” with physical devices, yet advanced social structures are also a form of technology. Laws, written language, the justice system, democracy, and social media are all human inventions that allow functioning on larger scales. And yet, they’re all more abstract than our biological tracking of individual relationships.
So, what happens when those systems break down? Probably the same thing that happened to the Ngogo group when its lynchpin members died, but on a much larger scale.
That means those social innovations are perhaps our most important technologies of all. And yet, compared to our physical technologies, they’ve been developed in a fairly ad hoc fashion. Perhaps a deeper understanding of the biological limitations that technology is helping us overcome would help us design future social technologies in a more deliberate and robust way.
