Within the dense tropical foliage of Uganda, researchers have documented primate behavior where the largest known congregation of wild chimpanzees (Pan troglodytes) engaged in violent intra-group conflict, eerily resembling a ‘civil war’.
This fatal antagonism represents the inaugural stark illustration of a brutal schism within a wild chimpanzee community, which ultimately fragmented into two adversarial factions.
Over an extended period, scientific observers witnessed these primates, who once coexisted harmoniously through shared living, foraging, mutual grooming, and coordinated patrols, progressively turning against one another, culminating in lethal animosity.
As one of humanity’s closest extant relatives, the social dynamics and interactions of these chimpanzees could offer profound insights into the evolutionary underpinnings of conflict and concord within our own species.
“It is facile to attribute current human polarization and warfare to ethnic, religious, or political cleavages,” the study’s principal authors, including evolutionary anthropologist Aaron Sandel from the University of Texas at Austin, elucidate.
However, these primates lack the same motivations for internal discord. It appears that shifts in social affiliations can independently sow discord among individuals of the same cultural group.
“This investigation prompts a reassessment of prevailing paradigms concerning human
collective aggression,” Sandel and his collaborators deduce in their academic publication.
Their amassed evidence, compiled from over three decades of continuous observation, adds significant weight to a long-standing scientific discourse. In the 1970s, the renowned primatologist Jane Goodall observed a chimpanzee populace in Tanzania devolve into two warring factions, igniting a four-year-long fatal confrontation.
These accounts gained global notoriety as a startling demonstration of non-human ‘warfare’; however, the granular details were scant, and subsequent critical analyses posited that the hostilities might have been precipitated by the provision of food resources during Goodall’s research tenure.
Chimpanzees are capable of brutal lethality, and in their natural habitats, they are documented to assault adjacent groups, potentially to secure or expand territory, or to plunder resources. Nevertheless, whether chimpanzees belonging to the same cultural affiliation engage in intramural ‘warfare’ has remained a subject of lesser clarity.
Genetic analyses of chimpanzees, for instance, indicate that enduring divisions within groups are exceptionally uncommon, with such incidents estimated to occur approximately once every 500 years.
This recent instance in Uganda might represent one such infrequent event. As far back as 1995, the Ngogo chimpanzee population in Uganda’s western Kibale National Park constituted a singular, expansive collective.
Subsequently, in 2015, shortly after the installation of a new dominant male, primatologists observed a perplexing behavioral divergence.
Within the same community, two distinct contingents began to coalesce, and reproductive pairings were exclusively observed between individuals of the same faction or clique.
“Our initial behavioral indicators suggesting a rupture were noted on June 24, 2015, when members of the Western and Central contingents converged in proximity to the central area of their domain,” the investigative cadre details.
“Rather than re-integrating in the customary fission-fusion pattern, the Western chimpanzees retreated, pursued by their Central counterparts. A six-week period characterized by mutual avoidance ensued. Such an extended duration of estrangement had not been previously documented.”
The former core of the Ngogo chimpanzee community transformed into a contested border, vigilantly monitored by males from both emergent factions. By 2017, social tensions escalated dramatically.
The Western contingent was numerically inferior to the Central group, yet it consistently initiated aggressive actions. During that year, Western chimpanzees engaged in combat, inflicting severe injuries upon the paramount male of the larger Central clique.
By 2018, the separation between these two sub-groups had solidified into a permanent schism across social, spatial, and reproductive dimensions. The females and their young ceased to forage even at the same fig tree.
Several years later, in 2021, the aggressive behavior extended to infants. Researchers directly witnessed Western chimpanzees abduct and terminate the lives of 14 infants belonging to the Central contingent.
Between 2018 and 2024, the Western chimpanzee factions were responsible for the demise of an average of one adult male and two infants annually.
These rates of lethality significantly surpass those estimated for inter-group aggression among chimpanzees, the researchers assert, and it is plausible that additional fatalities went unrecorded.
Over the course of the study, more than a dozen Ngogo Central chimpanzees perished under obscure circumstances. Frequently, these seemingly healthy individuals would simply vanish, their remains never located by the research team. It is a strong possibility that they, too, were victims of the Western ‘insurgency’.
“With a population approaching 200 individuals, including over 30 adult males, the Ngogo chimpanzee aggregation surpassed the typical size of other chimpanzee groups, potentially straining the capacity for maintaining intricate social bonds,” the research team postulates.
“While a change in alpha male does not unilaterally account for the Ngogo group’s fragmentation, it may have exacerbated underlying tensions between the two sub-groups.”
James Brooks, associated with the German Primate Center and uninvolved in this investigation, suggests that it is premature to draw definitive conclusions regarding the causes of this chimpanzee group’s rupture, or its broader implications for other primate populations and species, including humanity.
“Nevertheless,” he observes in a concurrent commentary, the study furnishes “critical data for… constructing models of the socioecological dynamics that underpin these phenomena.”
Humans may share 98.8 percent of their genetic blueprint with chimpanzees, yet genetic inheritance does not preordain destiny. Our interpersonal connections can precipitate destructive divisions, but they are also capable of fostering cooperation and empathy.
“Relational dynamics may exert a more profound causal influence on human conflict than is often acknowledged,” propose Sandel and his co-authors.
“In certain contexts, it may be within the subtle, everyday gestures of reconciliation and renewed association between individuals that avenues for achieving peace can be discovered.”
The findings of this research were officially published in the journal Science.
