A civil war that has raged for almost a decade. A community torn into two factions: a large central group and a smaller western one. Neighbours who once held hands now launching raids, ambushing and stalking each other.
In months, a new alpha had begun to dominate the community. With no elders to broker reconciliation, a small western group drifted away, under a less-aggressive leader of their own. The two factions have faced off routinely ever since, in clashes centred on the region’s resources. This gang war has been on for so long, there’s even a movie about it. We’ll have more on this in a bit. Their findings were published in PNAS this February. A DIFFERENT TACK Could animals, including some of these species, evolve to live differently amid changing conditions? There is precedent for this. Among the langurs of South Asia, the stomach plays a role in keeping peace. “Langurs have compound stomachs that allow them to slowly extract nutrients from their food. Elsewhere, the primates known as northern muriquis, in Brazil’s Atlantic Forest, are even gentler and more peaceful. They avoid direct contest altogether. Their lack of hierarchy helps them share resources and partners without hostility. It also helps that males and females are remarkably similar in size and build. Males do not threaten or attack young muriquis at all. Where would homo sapiens sapiens have fallen, on the scale of peace-to-aggression, in the wild? “It is undeniable that human prehistory and primate societies show evidence of extreme violence and inequality. That’s a heartening thought: that we might, at our core, have more in common with the northern muriqui than with Jackson and Miles.
It likely started in 2014, researchers say, when a cluster of chimpanzee elders were wiped out by a respiratory illness. The docuseries Chimp Empire, now streaming on Netflix, follows the world’s largest-known community of wild chimpanzees (the original undivided group numbered about 200) in the Ngogo rainforest. “Egalitarianism, tolerance and cooperation are less showy, and therefore have tended to go under-reported and receive less attention.
“We were surprised by the dramatic change in behavior after ants had been exposed to ozone,” Markus Knaden, who led the study at Max Planck Institute for Chemical Ecology, said in a statement. This has allowed their societies to evolve to be less aggressive and less despotic,” says biological anthropologist Ekanayake-Weber. “If someone gets out of line, the others usually remind them of the ‘rules’ through gestures such as gentle embraces,” says Karen Strier, a primatologist at University of Wisconsin-Madison who has researched the species for over four decades. Aggression, here, isn’t a behaviour that the animal’s society tends to reward, Strier says. However, it is my view that this has been over-emphasised,” says Ekanayake-Weber.
But chimps, it turns out, are not alone in such behaviour. Capuchin monkeys, banded mongooses and even ants can see hierarchical societies devolve into chaos, with deadly consequences, amid threats to key areas such as territory, food and potential mates. This takes on increased significance amid the climate crisis, where we can realistically expect to see resources dwindle and habitats change more dramatically than before. Where are researchers looking, for clues on how such shifts in behaviour could evolve? THE KIBALE CIVIL WAR First, the chimpanzees. Coveted fruit trees lie at the heart of the conflict. The central group patrols a sort of border at the periphery of a dense swathe of these trees. They continue to patrol these, even as their numbers fall, and despite the death of their leader. There is speculation that another alpha has since taken over, though observations of the group have not been conclusive. The western faction, meanwhile, has been altering how it operates and becoming more aggressive. They still patrol a far smaller territory and remain more loosely controlled. There is no equivalent, for instance, of the late Jackson’s belligerent lieutenant, Miles, who used his massive size to keep troops in order, subdue rivals, and back his leader during dominance displays.
Chimp Empire was filmed through 2021, at Kibale National Park in Uganda. As of April, fighting continued and the known toll stood at seven adult males and 17 infants. That alpha chimp, whom the series makers named Jackson, died in 2022, following an attack by the western group.
As of December, its numbers have grown to 108, while numbers in the other faction have dropped to 76. A 33-year study on this behaviour was published this year, by researchers at University of California, Los Angeles (UCLA). Because this lets them claim territory from smaller groups, thus ensuring access to crucial resources such as water, food and shade, the white-faced capuchins here have occasionally opted to live in larger groups, despite the strain of having more mouths to feed,. Because they posed a threat, but because the gas altered their odour signature (in as little as 20 minutes of exposure), causing colleagues and neighbours to mistake them for hostile invaders, not.
But the western cluster is killing at a growing rate. It looks at the moment as if the central group could eventually be decimated. But this war has sprung too many surprises for anyone to be able to predict with certainty what will come next. COMPETING FOR COVER In Costa Rica, meanwhile, monkeys have shown a tendency to coalesce, also with the idea of cornering lush territory. Climate stress and resource scarcity are altering social networks and increasing competition and aggression, she adds, especially in highly social animals such as primates. A DEADLY DATING GAME In Uganda, dominant female banded mongooses engineer conflicts with rival groups to distract the males in their clan, so they can mate outside their tightly knit community. Meanwhile, in Germany, rising air pollution has been shown to cause a different kind of civil war, with ants attacking members of their own colonies. When ants from six different species were exposed to air with very high levels of ozone, they were attacked upon their return to the colony.
We can expect to see more of this, says Marcy Ekanayake-Weber, a biological anthropologist at University at Albany in New York. These intergroup fights can be deadly, with multiple casualties, “but if they succeed, the resulting pups will be genetically more diverse, bigger, and more likely to survive,” a 2020 study by Michael L Wilson of University of Minnesota stated, in the journal PNAS.
