In the world of primatology, a fascinating and somewhat unsettling discovery has been made, shedding light on the complex social dynamics of our closest living relatives, the chimpanzees. This story, which reads like a tragic drama, unfolds in the lush forests of Uganda's Kibale National Park, where a once-harmonious chimpanzee community descended into a bloody civil war.
The narrative begins with primatologist Aaron Sandel, who, in 2015, witnessed a small group of Ngogo chimpanzees displaying nervous behavior, a stark contrast to their usual camaraderie. This moment, in hindsight, marked the beginning of a years-long conflict that would divide a once-unified group.
Published in the journal Science, Sandel and his colleagues' study documents what is believed to be the first observed civil war among wild chimpanzees. While chimpanzees are known for their aggressive behavior towards outsiders, the idea of a unified group turning against itself is a disturbing parallel to human behavior.
"Cases where neighbors kill neighbors are more troubling," Sandel observes, "as they get closer to the human condition. How can we reconcile our ability to cooperate with our propensity for turning on each other?"
The researchers' extensive observations, spanning over three decades, revealed a permanent split in the largest known group of wild chimpanzees. From 1995 to 2015, the group remained socially cohesive, but a shift in dynamics led to the emergence of two distinct groups by 2018: the western chimps and the central chimps.
The consequences of this division were dire. Over the following seven years, the western group launched 24 coordinated attacks on the central group, resulting in the deaths of at least seven adult males and 17 infants.
This rupture and civil war may not be unique. Scientists speculate that a similar event occurred in the 1970s within the chimpanzee group in Gombe, Tanzania, observed by the renowned primatologist Jane Goodall. However, our limited understanding of chimpanzee behavior at the time prevented a full appreciation of the rarity of such in-group violence.
In the case of the Ngogo chimps, researchers suggest that a change in social hierarchies, coupled with the deaths of several key older individuals and a disease outbreak, contributed to the group's fracture.
"Their abrupt deaths likely weakened connections among the neighborhoods, making the group vulnerable to polarization when the alpha change occurred," Sandel explains.
This study has important implications for ape conservation, as chimpanzees face the threat of extinction. Based on genetic evidence, these civil wars are believed to occur only once every 500 years. However, human activities that disrupt social cohesion, such as deforestation, the climate crisis, and disease outbreaks, could make such inter-group conflicts more frequent, Sandel warns.
Brian Wood, an evolutionary anthropologist, highlights the strategic gains of the western chimps in attacking their former community members, increasing their Darwinian fitness by decreasing the survival and reproduction of their competitors.
Sylvain Lemoine, a professor of biological anthropology, emphasizes the importance of social ties and network connectivity as the cement of group cohesion, noting that these ties can be fragile in specific circumstances, especially when they rely on a few key individuals.
This story serves as a powerful reminder of the complex social dynamics and potential for conflict within chimpanzee communities, offering a unique perspective on the human condition and the fragility of social cohesion.
