Chimpanzees in Uganda's Kibale National Park wage lethal 'civil war', research reveals
A new report documents a lethal schism in a chimpanzee community in Uganda's Kibale National Park, where researchers have been continuously monitoring the group since 1995. The conflict, marked by 'collective attacks' and 'territorial patrols,' has led to infanticide and hardened group identities, suggesting the roots of human social behavior are embedded in our shared evolutionary history.
ABC News — Uganda's Kibale National Park is home to the largest-known group of wild chimpanzees in the world. Amid the lush greenery, hundreds of the endangered primates groom, play, forage and interact.
Their contact with human beings is minimal. There are no cities bordering their forest habitat. Even so, their remote home became the scene of a primitive "civil war" — one that dramatically changed their group. It quickly turned lethal.
The schism in their community has been documented for the first time in a new report published by a team of researchers based out of the University of Texas. The peer-reviewed report, published in the journal Science this week, reviewed decades of shifting social ties among the chimpanzee community. Researchers had been continuously monitoring the group since 1995, according to Aaron Sandel, an anthropologist at the University of Texas and co-director of the Ngogo Chimpanzee Project. "I started studying them in 2012 when I began my PhD," he told the ABC. "Initially I was studying social bonds and how relationships develop during adolescence and young adulthood. "I spent 15 months in the forest for my dissertation research from 2014 to 2015. " That was when everything changed.
'Cliques' give way to first signs of trouble According to the report, the group had been part of a single large community in Ngogo for the first two decades of research. Between 1998 and 2014 — the "pre-fission" era, before things went sour — the group existed in overlapping "clusters" throughout the year.
The chimpanzees moved between what researchers called the "Western cluster" and the "Central cluster", with many switching groups from one year to the next. "We developed a method to test whether individuals formed cliques in which they occurred in the same cluster more than expected by chance," the report said. "One of these cliques comprised of three adult males who later became the core of the post-fission Western group. "These males were consistently together, even as they joined clusters who would later belong to the [rival] Central group."
The first sign of trouble, the report said, came on June 24, 2015. On that day, members of the western and Central clusters approached each other near the centre of the group's territory. "Rather than reuniting … the Western chimpanzees ran away, and the Central chimpanzees chased them," the report said. Members of the two groups avoided each other for six weeks afterwards — something the report noted had not been seen before. From then on, the group's separation or modularity increased "sharply", with 2015 marking the beginning shift from one fluid group to two rival groups. By 2018, a permanent fission was "evident based on social, special, and reproductive data". "What was once the centre of a shared territory had become a border," the report said.
Findings match Jane Goodall's Tanzania research The idea of chimps showing lethal aggression to outsiders wasn't new, but turning violent towards their former friends was, according to Rebecca Hendershott. Dr Hendershott, a primatology lecturer at the Australian National University, said the report broke down "what we know about human superiority".
"There's an assumption that everything humans do is underwritten by complex social and cultural dynamics, and that may or may not be true," she said. "The common assumption is that … [animals] couldn't possibly have the complexity that we have because we're so special. "And I feel like a lot of primatologists are very aware that we are not that special, and that everything that we think is special about us exists on a continuum."
One set of images included in the report, she added, stood out to her. "[The picture] had four males doing reassurance with each other," she said. "And then a couple years later, three of those males killing the other. "And that was particularly emotional or surprising to me because to see them fear grimacing and embracing as a form of reassurance, you do that with people you trust, right? " You don't just seek reassurance from anybody. And so to me, that really highlighted that these were friends. "
Maria Sykes, the chief executive of The Jane Goodall Institute Australia, said the findings were "entirely consistent" with Dr Goodall's initial research in Tanzania. "Generically, human share around 98-99 per cent of our DNA with chimpanzees, making them closer to us than any other living animal, including gorillas," Dr Sykes said. "This biological proximity is reflected in behaviour. "Chimpanzees demonstrate complex social relationships, cooperation empathy and grief — but also organised aggression and lethal conflict."
Jane Goodall's legacy In the chimp world, there was the time before Jane Goodall and the time after. The evidence of sustained lethal conflict between the animals in this study was particularly notable, she added. "This provides strong evidence that the capacity for intra-group conflict does not depend on human-specific cultural constructs such as ideology or religion," she said. "[It can] can arise from shifts in social relationships and group dynamics alone. "Studies like this reinforce the extent to which the roots of human social behaviour — including both cooperation and conflict — are deeply embedded in our shared evolutionary history."
'Collective attacks', 'territorial patrols' and chimpanzee infanticide Things turned violent following the schism, according to the report. Western chimpanzees killed many from the Central group in what researchers called a series of "collective attacks". Members of the Western group made "territorial patrols" into Central territory, sparking at least six lethal attacks on adult males. "Beginning in 2021, lethal aggression expanded to infants," the report said. "We observed 144 infanticides … and inferred three additional infanticides by Western males against Central infants."
The report suggested several things might have contributed to the split, including the sheer size of the group, which at one point was made up of nearly 200 chimpanzees and more than 30 adult males. That may have led to "heightened feeding competition", "reproductive competition" and weakened social ties following the deaths of several chimps in early 2014.
The group is still being observed, according to Dr Sandel. "And the conflict is ongoing," he said. "This paper just provides our first synthesis of what happened — the group splitting and dividing the territory in two. "But it's just the beginning. Our ongoing work is focused on the cause and consequences. "A key aspect of this event is that group identities are shifting — chimpanzees are killing their former community members."
Asked whether the group could ever resolve their conflict, he said: "At this point I think it's too late for the Ngogo chimps to reconnect. "Maybe in the first year or so [they could have]. Now, however, I think the new group identities have hardened."