According to researchers, chimpanzees in Uganda are engaged in a bloody "civil war."

 

This shows adult male chimpanzees of one group attacking a male chimpanzee of another group in 2019(Image:Reuters)

The world's largest known group of wild chimpanzees has split and been locked in a vicious "civil war" for the last eight years, according to researchers.

 It is not clear exactly why the once close-knit community of Ngogo chimpanzees at Uganda's Kibale National Park are at loggerheads, but since 2018 the scientists have recorded 24 killings, including 17 infants.

 Aaron Sandel, the lead author, stated, "These were chimps that would hold hands." "Now they're trying to kill each other."

 The study, published in the journal Science, says the intensity and duration of the violence may inform how early human conflict developed.

READ MORE: Chimp rescued as a baby from circus abuse turns 30

Sandel, an anthropologist from the University of Texas in the US, and co-director of the Ngogo Chimpanzee Project, says chimpanzees are "very territorial", and have "hostile interactions with those from other groups".

 "[It's] like a fear of strangers," he told the Science podcast. However, Sandel claimed that the nearly 200 Ngogo chimpanzees had coexisted peacefully for several decades.

There were divided into two sets - known to researchers as Western and Central - but they had existed overall as a cohesive group.

 Sandel said he first noticed them polarising in June 2015, when the Western chimpanzees ran away and were chased by the Central group.

 He explained, "Chimpanzees are sort of melodramatic," that after arguments, there would typically be "screaming and chasing," followed by grooming and cooperation. However, following the disagreement in 2015, the researchers observed that the two sets avoided each other for six weeks, with interactions becoming less frequent. Sandel described them as "a little more intense, a little more aggressive" when they did occur. Members of the Western group began attacking the Central chimpanzees in 2018 after the two groups split up. In 24 targeted attacks since the split, at least seven adult males and 17 infants from the Central chimps have been killed, the study found, although the researchers believe the actual number of deaths are higher.

 The researchers believe many factors such as the group size and subsequent competition of resources, and "male-male competition" for reproducing may be to blame.

However, they point to three possible triggers: The first was the 2014 death of five adult males and one adult female for unknown reasons, which may have weakened social ties between subgroups and disrupted social networks. The following year, there was a change in the alpha male, which the study says coincided with the first period of separation between the Western and Central groups.  It explained, "Chimpanzees' aggression and avoidance can increase as a result of changes in the dominance hierarchy." The third factor was the deaths of 25 chimpanzees, including four adult males and 10 adult females, as a result of a respiratory epidemic, in 2017, a year before the final separation.  One of the adult males who died was "among the last individuals to connect the groups", the research paper said.

 According to Sandel and his colleagues, their findings inspire people to reconsider their prior understanding of human conflict and warfare. "In the case of the Ngogo fission, individuals who lived, fed, groomed and patrolled together for years became targets of lethal attacks on the basis of their new group membership," they wrote in the paper.

 They went on to say that "relational dynamics may play a larger causal role in human conflict than often assumed" if chimpanzees, one of the species that are genetically closest to humans, were able to do so without human constructs such as religion, ethnicity, and political beliefs. It was a "reminder of the danger that group divisions can present to human societies," according to German primate center researcher James Brooks. Commenting on the study in Science, he wrote: "Humans must learn from studying the group-based behaviour of other species, both in war and at peace, while remembering that their evolutionary past does not determine their future."

Source: BBC