Tag: primatology

  • The Ngogo Chimpanzee War: The First Documented Civil War in a Non-Human Species

    On the last full day of his life, a chimpanzee named Basie woke at dawn in a tree nest he’d built from branches and leaves, surrounded by other chimps dozing in their own nests, as he’d done nearly every day for 36 years in the Kibale National Park rainforest in Uganda. He spent an ordinary day swinging between trees and eating figs. As daylight faded, a patrol of about 13 adult chimpanzees from the opposing faction arrived. Three surrounded him. He jumped from a tree. Ten piled on him on the ground, biting him. Basie’s killers were chimpanzees he had grown up with — individuals he had groomed, traveled with, and defended territory alongside for decades. His death in 2019 was the second casualty in what researchers now call the Ngogo chimpanzee civil war, an eight-year conflict that has killed at least 28 chimpanzees, including 19 infants, and that a study published in Science on April 9, 2026, has documented in detail that primatologists say is unprecedented.

    What happened

    The Ngogo chimpanzee community was the largest known group of wild chimpanzees on earth — approximately 200 individuals living in relative cohesion in Kibale National Park for at least 20 years under continuous scientific observation since 1995. Chimpanzee communities typically number around 50. Ngogo was four times that. The group operated through a fission-fusion social structure — small parties formed and dissolved throughout the day as individuals moved around the territory foraging and socializing, but everyone belonged to the same community, shared the same territory, and collectively defended it against neighboring groups. Within the community, social relationships clustered around two primary neighborhoods that researchers named the Central and Western groups, but the boundary was porous. Chimps changed which cluster they associated with. Males groomed partners from both groups. Females mated across the divide. Key individuals — socially connected males who maintained relationships in both clusters — served as bridges holding the community together.

    Then those bridges collapsed. Several of the bridging males died from disease. A new alpha male rose to power, shifting the community’s political center of gravity. A respiratory disease outbreak further destabilized social networks. By approximately 2015, chimps in the Western and Central clusters began avoiding each other. The avoidance hardened into separation. By 2018, the division was permanent — two distinct communities with separate territories, separate social hierarchies, and no remaining social bonds between them.

    What followed was not a border skirmish between strangers. It was coordinated lethal violence between former companions. The Western faction — numerically smaller, starting at about 76 individuals — launched targeted raids into Central territory. Groups of adult males would patrol into enemy territory, locate isolated individuals, and attack with overwhelming numbers. The violence was graphic: sustained group assaults, biting, mutilation. From 2021, the Western raiders began targeting and killing infants — a pattern that primatologists associate with territorial expansion, as infanticide eliminates the offspring of rivals and can make females sexually receptive sooner.

    The Western faction’s campaign has been described as a “one-sided rout.” Their numbers grew from 76 to 108 over the course of the conflict. The Central faction suffered a stepwise decline. John Mitani, a professor emeritus at the University of Michigan who had been studying the Ngogo chimps for two decades when the violence started, told NBC News he is concerned the Central group is “doomed.” The war is ongoing. The 2026 Science paper covers data through 2024, but lead author Aaron Sandel of the University of Texas at Austin confirmed that further attacks have occurred in 2025 and 2026.

    Why it matters

    This is only the second documented case of a chimpanzee community splitting and going to war with itself. The first was the Gombe Chimpanzee War of the 1970s, observed by Jane Goodall in Tanzania, where a community called the Kasakela fissioned and the splinter group (the Kahama) was systematically hunted and destroyed over four years. The Gombe war was groundbreaking but limited by the observational methods available in the 1970s. The Ngogo study benefits from 30 years of continuous demographic data, 24 years of systematic behavioral observations, a decade of GPS tracking, and structured social network analysis — a dataset that Gombe never had. Genetic evidence suggests that permanent community fissions in chimpanzees are extraordinarily rare, occurring roughly once every 500 years. Researchers have now documented two in 50 years of field primatology, which either means the estimate is wrong or scientists have been spectacularly unlucky — or lucky, depending on your perspective.

    The social network data is what makes the Ngogo study new. The 2026 Science paper mapped the social ties between individuals across the entire community for years before, during, and after the split. What they found is that the division didn’t happen along genetic lines, or resource boundaries, or any clear ecological gradient. It happened along social network lines. When the bridging individuals who maintained connections between the two clusters died or were removed, the network fragmented — and fragmentation preceded violence by approximately three years. The chimps didn’t fight and then separate. They separated and then fought. Avoidance came first. Identity formation second. Lethal violence third.

    Aaron Sandel told BBC Science Focus that the study provides “a window into the chimpanzee mind that’s really rare” — the transition from friend to enemy, visible in behavioral data over a decade. The implication for understanding human conflict is the part that’s getting the most attention. In humans, collective violence is typically explained by cultural differences — ethnicity, religion, language, ideology — that bind groups together and generate hostility toward outsiders. But the Ngogo chimps had no cultural markers distinguishing the two factions. They spoke the same calls, ate the same food, lived in the same forest, and had mated with each other for years. The split wasn’t driven by what made them different. It was driven by the decay of what had kept them connected.

    Sandel’s conclusion is pointed: if chimpanzee civil wars emerge from the breakdown of interpersonal relationships rather than from intergroup differences, then human peace interventions that focus on cultural diplomacy — learning about the other side’s traditions, bridging ideological divides — may be missing the more fundamental mechanism. “What we have to do is maintain interpersonal relationships,” Sandel told Scientific American. “If we can reunite — even in the face of conflict — then I think that’s a recipe for maintaining peace.” Liran Samuni of the German Primate Center, who was not involved in the study, noted that even before the split, the Ngogo community was “one of the chimpanzee communities that was most violent in terms of encroaching on neighbors” — they had previously killed at least 21 chimpanzees from other groups and expanded into their territory. The civil war is new. The violence isn’t.

    The Gombe parallel

    Anne Pusey, who conducted fieldwork at Gombe until 1975 during the beginning of that war, told the Washington Post that the circumstances preceding both conflicts were “similar and shocking”: a shortage of mating-age females, the death of socially central older males, a change in alpha male, and disease. In both cases, social bonds that had been stable for years degraded rapidly once key connective individuals were removed from the network. Joseph Feldblum, an evolutionary anthropologist who has studied the Gombe data, said the Ngogo findings validate the earlier observations: “This sort of behavior, while rare, is part of the natural course of chimpanzee behavior.”

    The baboon politics research on coalition formation and dominance hierarchies, the chimpanzee tool use literature documenting cultural transmission across generations, and the dolphin signature whistle work demonstrating individual identity in non-human social systems all converge on the same insight the Ngogo war makes visceral: complex social cognition isn’t an abstract capacity. It’s the infrastructure that holds societies together — and when the infrastructure fails, the consequences in chimpanzee communities look disturbingly like the consequences in human ones. Former friends become lethal enemies not because something changed about who they are, but because the relationships that made them “us” instead of “them” stopped being maintained.

    We cover the Ngogo war alongside mirror neurons, corvid intelligence, animal deception, and 20 other investigations into what animal minds reveal about the architecture of social life across our Animal Culture & Knowledge course — where the question isn’t whether animals have societies but what happens when those societies break.

  • Chimpanzee Tool Traditions: Different Populations, Different Technologies

    In the Goualougo Triangle of the Republic of Congo, chimpanzees harvest termites using a two-tool system. First, they manufacture a thick, sturdy puncturing stick from a specific plant species and drive it into the soil to breach the outer wall of a subterranean termite nest. Then they switch to a separate fishing probe—thinner, more flexible, often with the tip deliberately frayed by pulling it through their teeth to create a brush-like end—and insert it through the access tunnel they’ve just made. Termites bite the frayed fibers, the chimpanzee withdraws the probe, and eats them off the bristled end. The whole operation requires selecting the right raw materials, manufacturing two distinct tools in the correct sequence, and knowing how to modify one of them to improve its efficiency. It is, by any reasonable definition, a technology.

    Nine hundred kilometers east, at Gombe in Tanzania, chimpanzees also fish for termites. But they use a single tool—a simple probe stripped of leaves, inserted directly into exposed holes in the mound—and they don’t puncture, don’t use tool sets, and don’t fringe the tips. Same species. Same resource. Same basic objective. Completely different technique. And when researchers compared these two populations in a study published in PNAS, they found that in Goualougo—where the task is more complex—mothers were significantly more likely to actively share tools with their offspring and facilitate learning, something that barely happens at Gombe, where the task is simple enough that young chimps figure it out by watching.

    That’s not instinct varying by region. That’s culture. And the chimpanzee evidence for culture is, at this point, about as close to settled as anything in behavioral ecology gets.

    The 1999 paper that changed the field

    The landmark study was Andrew Whiten’s 1999 paper in Nature, which synthesized data from the seven longest-running chimpanzee field sites across Africa—151 combined years of observation. The analysis identified 39 distinct behavioral patterns, including tool use, grooming styles, and courtship displays, that were customary or habitual in some communities but entirely absent in others, even when ecological and genetic explanations had been ruled out. The behavioral repertoire of each community was itself distinctive—not just a few isolated differences but a combinatorial profile of dozens of traditions that, taken together, made each population culturally unique.

    That’s worth sitting with. Before 1999, “culture” in the biological sciences was essentially reserved for humans. Other animals had “traditions” or “behavioral variation” or, if you were being generous, “proto-culture.” Whiten’s paper didn’t just add chimpanzees to the list of species with cultural variation—it showed that the scope and combinatorial complexity of that variation was without parallel in any non-human species. Not one tradition. Not three. Thirty-nine, distributed across communities in patterns that looked less like random variation and more like the kind of between-group differences you’d see comparing human societies.

    The paper used what’s called the “method of exclusion”—if a behavior is present in one community and absent in a neighboring community with access to the same raw materials, the same prey species, and similar genetic backgrounds, and if that behavior is transmitted socially rather than reinvented independently, then the most parsimonious explanation is cultural transmission. It’s not a perfect methodology—proving a negative (that ecology doesn’t explain the difference) is always harder than proving a positive—but it was rigorous enough to shift the consensus.

    The tool traditions themselves

    The catalog of chimpanzee tool behaviors now documented across Africa is staggeringly diverse, and the geographic specificity of individual techniques is what makes the cultural interpretation so compelling.

    Nut cracking with stone or wooden hammers is practiced by chimpanzee populations in West Africa—in Côte d’Ivoire, Guinea, Liberia, and Sierra Leone—but is completely absent in East and Central African populations, despite the availability of suitable nuts and hard surfaces. The Taï Forest chimpanzees in Côte d’Ivoire select stone hammers of appropriate weight for the hardness of the nut species being cracked, transport hammers to anvil sites they remember from previous visits (sometimes carrying them over a kilometer through the forest), and teach the technique to juveniles through years of observation and practice. Young chimps at Taï spend roughly four to five years learning to crack Coula nuts and seven years to crack the harder Panda nuts. That’s an apprenticeship, not a light-switch moment.

    Ant dipping—using a stick to harvest driver ants or safari ants from their nests—varies in technique across populations in ways that map onto geography rather than ecology. Some populations use short sticks and eat the ants directly off the tool with their lips. Others use long sticks, wait for a mass of ants to swarm up the tool, then sweep them off with a single hand motion into their mouth. The technique choice correlates with community membership, not with the ant species or the physical properties of the nest. When researchers at the Taï site compared neighboring communities separated by only a few kilometers, they found that the communities used different lengths of ant-dipping tools and different techniques—despite inhabiting functionally identical habitat with the same ant species available. The difference was social, not ecological.

    Spear hunting is one of the most striking recent discoveries. At Fongoli in southeastern Senegal, Jill Pruetz documented chimpanzees fashioning wooden spears from branches—stripping side branches, sharpening the tip with their teeth—and thrusting them into tree cavities to stab bushbabies, small nocturnal primates that shelter in hollow branches during the day. This has not been observed at any other site. It’s a behavior that involves tool manufacture, planning (they modify the spear before approaching the tree, not after), and lethal predatory intent. Female and juvenile chimps at Fongoli do this more frequently than adult males, which inverts the usual pattern of male-dominated hunting in chimpanzees and suggests the spear technique may be an equalizer—a technology that compensates for the strength advantage that adult males have in manual capture.

    Honey dipping—using sticks to extract honey from beehives—shows variation across the entire species range. Central African populations at some sites use complex multi-tool sets (a pounder to break open the hive, a collector to extract the honey), while West African populations that eat honey frequently often don’t use tools at all. A 2021 study in Guinea-Bissau documented honey-dipping tools for the first time in the westernmost chimpanzee populations, adding new data points to a behavioral map that’s still being filled in. The variation suggests that honey-dipping technology has been invented and elaborated independently in different populations, rather than spreading from a single origin—which is convergent cultural evolution, a concept that makes the human parallel even more interesting.

    Why this isn’t just “smart animals being smart”

    The critical distinction between culture and individual intelligence is social transmission—behaviors that are learned from others, maintained within a group over generations, and resistant to disruption by individual innovation. If every chimpanzee independently figured out how to crack nuts, that would be intelligence. What makes it culture is that the technique is passed from mother to offspring through years of observation and practice, maintained within populations even when individuals migrate between groups, and differentiated between neighboring communities in ways that can’t be explained by the environment.

    The conformity data is particularly striking. In a series of experiments by Andrew Whiten and colleagues, researchers introduced two different techniques for solving the same food-extraction problem into separate captive groups by training a single high-ranking female in each group. The technique spread through each group via social learning. But here’s the part that matters: some individuals in each group independently discovered the alternative technique—the one that had been seeded in the other group—and then abandoned it in favor of the locally dominant method. They conformed. They had a working solution, discovered a different working solution, and reverted to the one everyone else was using. That’s not problem-solving. That’s peer pressure. That’s culture.

    In the wild, the same conformity pattern has been documented with migrating females. When a female chimpanzee transfers from one community to another—which is the normal dispersal pattern—she adopts the tool traditions of her new community, even if she was proficient in a different technique at her birth community. William McGrew, one of the founding figures of chimpanzee cultural primatology, pointed out the thought experiment: imagine a female from Gombe transferring to Goualougo. If she persisted in fishing for termites the Gombe way—single probe, no puncturing stick—she’d fail, because the Goualougo termite nests require the puncturing step she never learned. She’d have to adopt the local technology or go hungry. The technology is the community’s intellectual property, and you either learn it or you don’t eat.

    What this tells us about early human culture

    The reason chimpanzee tool traditions matter beyond primatology is that chimpanzees are one of our two closest living relatives (bonobos being the other), and the last common ancestor we shared lived roughly six to seven million years ago. The cultural capacity documented in living chimpanzees—multiple traditions, conformity bias, social transmission across generations, geographically specific tool-use techniques—represents either a shared ancestral trait or an independently evolved one. Either way, the implication is that the cognitive and social infrastructure for culture was present in the hominin lineage long before stone tools show up in the archaeological record around 3.3 million years ago.

    The emerging field of “primate archaeology” is making this connection explicit. Researchers are applying the same archaeological methods used to study early human tool sites—analyzing raw material selection, tool morphology, wear patterns, and spatial distribution of discarded tools—to chimpanzee termite-fishing sites and nut-cracking stations. The Kasekela and Mitumba communities at Gombe, separated by just a few kilometers, produce termite-fishing tools that are measurably different in length and width, made from different selections of raw materials, even though both communities have access to the same plant species. That’s the kind of between-population variation in material culture that, if it showed up in a 2-million-year-old hominin site, would be published in Nature and generate a press cycle about “the origins of technology.”

    It’s already happening. It’s just happening in chimpanzees, which makes it less glamorous and more informative.

    We cover chimpanzee tool traditions—alongside whale dialects, corvid problem-solving, fish social learning, and the full breadth of non-human cultural transmission—across our Animal Culture & Knowledge course. If the spear-hunting bushbaby story made you rethink what “culture” means, the course goes considerably deeper.