Wild chimpanzees recorded waging ‘civil war’ with coordinated attacks between two groups | Primatology

In June 2015, primatologist Aaron Sandel was quietly observing a small cluster of the Ngogo chimpanzee group in Uganda’s Kibale national park when he noticed something odd. As other members of the chimpanzee group approached the forest, the chimpanzees in front of him began to exhibit nervous behavior. They grimaced and touched each other reassuringly, acting as if they were meeting strangers rather than close friends.

Looking back, Sandel said that moment was the first sign of what would become a years-long bloody conflict between what was once a close-knit group of chimpanzees.

a new to work In a study published this week in the journal Science, Sandel and colleagues document what may be the first “civil war” observed in wild chimpanzees. While chimpanzees have long been known to engage in deadly attack campaigns against strangers, witnessing a once-united group turn against itself is something new and very human.

“Situations where neighbors kill neighbors are more disturbing and in a way approach the human condition. How do we create this contradiction within ourselves where we can cooperate but at the same time very quickly become enemies of each other?” said Sandel.

“These changing group identities and dynamics that we see in human civil war are rarely paralleled in other animals, but there are parallels in chimpanzees.”

Researchers used more than three decades of behavioral observations of a well-studied group of chimpanzees to identify a permanent split in the world’s largest known group of wild chimpanzees. Although chimpanzees were socially cohesive from at least 1995 to 2015, something in the group’s dynamics changed, and by 2018 two distinct groups had emerged: western chimpanzees and central chimpanzees.

With the two groups consolidated, members of the western group launched 24 sustained and coordinated attacks on the central group over the next seven years, killing at least seven adult males and 17 infants.

Scientists think that a similar rupture and civil war may have occurred in the chimpanzee group in Gombe, Tanzania, in the 1970s, as observed by the famous primatologist Jane Goodall. But our basic understanding of chimpanzee behavior at the time was too limited to fully appreciate the rarity of intragroup violence.

in case Ngogo chimpanzeesA change in social hierarchies could explain group fracturing, leading to organized aggression and violence, the researchers said. The day Sandel observed the chimpanzees behaving strangely in 2015, early that morning, the alpha male of the group had grunted in obedience to another chimpanzee. However, the social structure of the group was also affected by the deaths of several important elderly individuals in the years before the split.

“Their sudden deaths probably weakened the connections between neighborhoods, making the group vulnerable to this polarization that happens when alpha shifting occurs,” Sandel said. “Then there was also a disease outbreak in 2017 that probably made the split inevitable or slightly accelerated it.”

This should cause some concern for the protection of monkeys, as Chimpanzees are in danger of extinction. Based on genetic evidence, these “civil wars” among chimpanzees likely only occur every 500 years, the study notes. But any human activity that disrupts social harmony — deforestation, climate crisis or disease outbreaks — could make such intergroup conflicts more common, Sandel said.

Brian Wood, an evolutionary anthropologist at the University of California Los Angeles who has also studied Ngogo chimpanzees but was not involved in the new research, said it is important to consider what a group might gain by attacking former community members.

In Darwinian fitness theory, which is a measure of how successful an animal is at passing on its genes, “you can increase your Darwinian fitness by increasing your own survival, increasing your reproduction, or increasing your reproduction.” By reducing the survival and proliferation of your competitors,” Wood said.

“And that’s what western chimpanzees do. After facing the onslaught of western chimpanzees, the central chimpanzees no longer lowest survival rate “This has never been documented in a wild chimpanzee community.”

Sylvain Lemoine, professor of biological anthropology at the University of Cambridge, said: “Here we have the first reported case in detail of what might qualify as civil war in the species… This shows that even in the absence of cultural group markers, social bonds and network connectivity are the cement of group cohesion, and that these bonds can become fragile in certain situations, especially when they rely on a few key individuals.”

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