Chimpanzee Civil War: Ngogo Group's Fatal Split Documented in New Study
In a groundbreaking discovery, wild chimpanzees in Uganda have been recorded engaging in what scientists describe as a civil war, with coordinated attacks between two factions that were once a unified community. This rare phenomenon, documented in a new study published in the journal Science, offers profound insights into primate behavior and its parallels to human conflicts.
The First Signs of Conflict
On a June day in 2015, primatologist Aaron Sandel was observing the Ngogo chimpanzee group in Uganda's Kibale National Park when he noticed unusual behavior. As other members of the wider group approached, the chimpanzees he was watching displayed nervousness, grimacing and touching each other for reassurance, as if anticipating strangers rather than companions. In hindsight, Sandel identified this moment as the initial indicator of a years-long bloody conflict that would erupt within the once close-knit group.
The study, led by Sandel and his colleagues, draws on over three decades of behavioral observations to detail the permanent split of the largest known wild chimpanzee group in the world. From at least 1995 until 2015, the chimps had maintained social cohesion, but a shift in group dynamics led to the emergence of two distinct factions by 2018: the western chimps and the central chimps.
Coordinated Attacks and Fatalities
Following the split, members of the western group launched 24 sustained and coordinated attacks on the central group over seven years. These assaults resulted in the deaths of at least seven adult males and 17 infants, marking a stark escalation in violence. While chimpanzees have long been known to exhibit lethal aggression toward outsiders, this case of a unified group turning on itself is unprecedented in wild observations.
Sandel emphasized the human-like nature of this conflict, stating, "Cases where neighbours are killing neighbours is more troubling and, in a way, it gets closer to the human condition. How do we have this seeming contradiction within us where we are able to cooperate, but then also very quickly turn on one another?" He added that such shifting group identities and dynamics, common in human civil wars, now have a parallel in chimpanzees.
Underlying Causes of the Split
Researchers attribute the group's fracture to changes in social hierarchies and key individual losses. On the day Sandel observed the strange behavior in 2015, the group's alpha male had grunted in submission to another chimpanzee earlier that morning. Additionally, the deaths of several older individuals in the years preceding the division likely weakened social connections among neighborhoods, making the group vulnerable to polarization.
Sandel explained, "Their abrupt death likely weakened connections among the neighbourhoods, which then made the group vulnerable to this polarisation that happened when the alpha change occurred. Then there was also a disease outbreak in 2017 that probably made the split inevitable, or expedited it slightly."
Historical Context and Conservation Implications
Scientists speculate that a similar rupture may have occurred in the 1970s within the chimpanzee group in Gombe, Tanzania, observed by primatologist Jane Goodall. However, limited understanding of chimpanzee behavior at the time prevented full appreciation of the rarity of in-group violence. The Ngogo study provides the first thoroughly reported case of civil warfare in the species, highlighting how social ties and network connectivity serve as the cement of group cohesion.
Sylvain Lemoine, a professor in biological anthropology at the University of Cambridge, noted, "It shows that, even in absence of cultural group markers, social ties and network connectivity are the cement of group cohesion, and that these ties can be fragilised in specific circumstances, especially when they rely on few key individuals."
From a conservation perspective, this civil war raises concerns for ape populations, as chimpanzees are threatened with extinction. The study estimates that such conflicts among chimpanzees likely occur only every 500 years based on genetic evidence. However, human activities that disrupt social cohesion—such as deforestation, the climate crisis, or disease outbreaks—could increase the frequency of inter-group conflicts, according to Sandel.
Evolutionary Insights and Future Research
Brian Wood, an evolutionary anthropologist at the University of California Los Angeles, who has studied the Ngogo chimpanzees but was not involved in the new research, discussed the Darwinian fitness implications. He stated, "In the theory of Darwinian fitness—a measure of how successful an animal is in passing on its genes—you can increase your Darwinian fitness by increasing your own survival, increasing your reproduction or by decreasing the survival and reproduction of your competitors. And this is what the western chimps have done. The central chimps, after facing the onslaught of the westerners, now have the lowest survivorship that has ever been documented in a wild chimpanzee community."
This study not only sheds light on the complex social behaviors of chimpanzees but also prompts further exploration into the factors that drive such violent divisions. As researchers continue to monitor these groups, the findings may inform broader understandings of animal behavior and conservation strategies in the face of environmental pressures.
