War of the Apes

Social animals rarely have conflict beyond hunting and territorial disputes. Wolves, bonobos, whales, and other highly social species almost never fight members of their own pack. Compare this to humans, who have waged war after war against members of their own species for religion, money, ideology, or ethnicity. Such wars — particularly civil wars — are often attributed to the cultural differences that distinguish groups from one another. But this raises a harder question: what actually creates those cultural fractures in the first place? In some cases, the answer is a clear geographical or environmental divide, but not always. A recent chimpanzee war has led researchers to question whether culture necessarily induces conflict, or whether conflict itself may drive groups apart.

The Ngogo chimpanzee tribe of over 200 apes is a well-studied group that resides in Kibale National Park, Uganda, and has been studied continuously since 1995. Part of the research has focused on building an understanding of the social relationships between all members. To do this, researchers constructed a graph with thicker lines connecting apes who spent more free time together, and thinner lines for those who rarely interacted. What they found was a cohesive community with constant interaction between everyone. There were two distinct friend groups in which apes socialised more closely with each other, but many members belonged to both groups, and nearly half of all chimpanzees were conceived by parents from separate groups. Given this, it was clear that the two groups — labelled the Western and Central groups — were just two flexible subsets of the larger community. 

One day, in 2015, everything changed. When a group of Western chimps and Central chimps met in the centre of their territory, the Western group started to run. The Central chimps started to chase them. Up until that moment, all the members were still communicating and frequently changing groups, yet for some reason, everything was different. After that, the two groups distanced themselves for six weeks. Things only got worse from there. The Western apes claimed a section of the territory for themselves and began patrolling, as did the Central apes. In 2017, one group of Western apes attacked a lone Central ape who had once been a part of their group. All ties had been severed.

In 2018, things escalated again. The Western group started patrolling into Central territory, leading to seven lethal encounters, but the chimps didn’t stop there. Over the next few years, there were seventeen infanticides and fourteen otherwise suspicious deaths. As far as chimpanzees go, this is all-out war.

Researchers posit a few ideas on how this happened in the absence of any cultural differences. One theory is that the death of just five group members (assumedly from natural causes) in 2015 disrupted the social network enough to cause complete fission, which implies that social structures are much more fragile than many would like to believe. Another idea is that the rise of one alpha male to dominance within the Central group caused enough tension and aggression within the group as a whole to cause a split, which naturally happened along the lines of weakest association.

Whatever the true reason may be, the results are worrying. Communities can be torn apart either by random chance or by just one or two bad actors with enough influence. If a group of chimpanzees — who share no religion, no ideology, and no ethnic identity — can fracture so completely and so violently, it suggests that the cultural differences humans cite as causes of war may be symptoms rather than sources. Researchers claim that “cultural traits remain essential for large-scale cooperation, but many conflicts may originate in the breakdown of interpersonal relationships rather than in entrenched ethnic or ideological divisions”. Whether these social developments underpin cultural divides or merely run alongside them remains to be seen. Maybe our social behaviour is a little less reasoned than we like to believe.

Image from Wikimedia Commons