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On a June day in 2015, primatologist Aaron Sandel was quietly observing a small cluster of the Ngogo chimpanzee group in Uganda\u2019s Kibale national park when he noticed something strange. As other members of the chimpanzees\u2019 wider group moved closer through the forest, the chimpanzees in front of him began to display nervous behaviour. They grimaced and touched each other for reassurance, acting more like they were about to meet strangers than close companions.<\/p>\n
In hindsight, Sandel said, that moment was the first sign of what would become a years-long bloody conflict between a once close-knit group of chimps.<\/p>\n
In a new study<\/a> published this week in the journal Science, Sandel and his colleagues document what may be the first observed \u201ccivil war\u201d in wild chimpanzees. While chimpanzees have long been known to wage campaigns of lethal aggression on outsiders, witnessing a once unified group turn on itself is something new \u2013 and very human.<\/p>\n \u201cCases 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?\u201d Sandel said.<\/p>\n \u201cThese shifting group identities and dynamics that we see in human civil war rarely have a parallel in other animals, but they do have a parallel in the case of chimpanzees.\u201d<\/p>\n The researchers drew on more than three decades of behavioural observations of the well-studied group of chimpanzees to determine the permanent split in the largest known group of wild chimpanzees in the world. While the chimps had been socially cohesive from at least 1995 until 2015, something shifted in the group\u2019s dynamics, and by 2018 two distinct groups had emerged \u2013 the western chimps and the central chimps.<\/p>\n With the two groups solidified, members of the western group made 24 sustained and coordinated attacks on the central one in the seven years that followed, killing at least seven adult males and 17 infants.<\/p>\n Scientists think that a similar rupture and civil war may have occurred in the 1970s within the chimpanzee group in Gombe, Tanzania, observed by the renowned primatologist Jane Goodall<\/a>. But, at the time, our basic understanding of chimpanzee behaviour was too limited to fully appreciate the rarity of in-group violence.<\/p>\n