A team of scientists has documented how a community of wild primates that once lived, ate, groomed and patrolled together gradually turned against each other until they became lethal rivals.
In the heart of Uganda’s rainforests, scientists have observed the largest known group of wild chimpanzees (Pan troglodytes) turn against yourselfin a process that resembles a “civil war”.
This deadly conflict, presented in a published this Thursday in the magazine Scienceis the first clear example of a violent split in a community of wild chimpanzees, which ended up fragmenting into two warring groups.
Over many years, scientists have tracked how wild primates that once lived, ate, groomed, and patrolled together were now gradually turning against each otheruntil they become lethal rivals.
As one of humanity’s closest living relatives, these chimpanzees and their social interactions can help us better understand their evolutionary roots. of “war” and “peace” in our own societies, says the .
“It is tempting to attribute polarization and war that occur today among humans ethnic, religious or political divisions”, write the authors of the study, led by evolutionary anthropologist Aaron Sandel, da University of Texas at Austin.
But These primates don’t have the same motives for internal conflicts. Instead, everything indicates that the change in social relations it can also open fractures between primates of the same culture. “This study encourages a reassessment of current models of collective violence humana”, Sandel and colleagues conclude.
The evidence gathered, based on more than 30 years of observations, feeds a decades-old debate. In the 1970s, , who died last year, observed in Tanzania a community of chimpanzees split into two rival factionstriggering a deadly battle that lasted four years.
These stories became famous around the world as a shocking example of non-human “war”but details were limited, and some critics have since argued that the clashes only occurred over food sources provided during Goodall’s investigation.
The chimpanzees can be brutal killers and, in the wild, they are known to attack other neighboring groups, possibly to defend and expand your territory or to seize resources. But the question of whether chimpanzees from the same cultural group enter into “civil war” has been less clear.
Chimpanzee genes, for example, suggest that permanent splits within groups are extremely rarewith an event of this type occurring only once every 500 years or so.
This recent case not Uganda could be one of those rarities. In 1995, the Ngogo chimpanzees in Kibale National Park in western Uganda were part of a single large group.
Then, in 2015, shortly after a new alpha male ascended to leadership, primatologists detected an inexplicable change. Two groups of chimpanzees began to form within the same community, and mating began to occur occurs only between males and females of the same nucleus or “clan”.
“Our first behavioral observations Suggestions of a split occurred on June 24, 2015, when members of the Western and Central nuclei approached each other near the center of their territory”, explains the research team.
“Instead of getting together, as would be usual in the fission-fusion pattern, western chimpanzees fled and the central chimpanzees chased them. A six-week period of avoidance followed. Never before had a such a prolonged period of avoidance”, they add.
What it used to be the center of the community of Ngogo chimpanzees became a border, patrolled by males on both sides. Then, in 2017, social tension reached breaking point.
O western group was much smaller than the central group, but it was he who started all the attacks. That year, western chimpanzees fought and seriously injured the alpha male of the largest central nucleus.
In 2018, the rupture between these two “clans” had become permanent in social terms, spatial and reproductive. The females and offspring even stopped feeding on the same fig tree.
A few years later, in 2021, aggression began to target the offspring. The researchers directly observed western chimpanzees kidnapping and killing 14 cubs from the central nucleus.
Between 2018 and 2024, western chimpanzees attacked and killed, on average, one adult male and two cubs per year.
According to the authors, these mortality rates far exceed existing estimates for aggression between chimpanzee groups, and there may have been even more cases. Over the years, more than a dozen chimpanzees from Ngogo’s central core died from unknown causes.
Often, these primates, apparently healthythey simply disappeared, and their bodies were never recovered by researchers. It is very possible that they too were killed by the Western “rebellion”.
“With almost 200 individuals, including more than 30 adult males, the Ngogo chimpanzee group exceeded the size of other groups of chimpanzees, which may have put pressure on their ability to maintain social relationships”, says the research team, as a hypothesis.
“Although the alpha male change alone does not explain why Ngogo’s group was split, it may have amplified tensions between the two groups,” say the study authors.
James Brooksfrom the German Primate Center, who was not involved in the research, considers that it is too early to draw firm conclusions about the reasons for this rupture in the chimpanzee group, or about what this could mean for other groups and species, including ours.
“Still,” he writes in a perspective piece accompanying the study, the work provides “crucial information for modeling socio-ecological processes that underlie these events.”
Humans may share 98.8% of their DNA with chimpanzees, but genes are not destiny. Our relationships with others can fuel deadly divisions, but they can also foster cooperation and compassion.
“Relational dynamics can play a causal role greater in human conflicts than is often assumed,” Sandel and colleagues suggest. “In some cases, it is in the small, everyday gestures of reconciliation and reunion between individuals that we can find opportunities for peace”.
