There is a common misconception that bonobos never fight; if tensions are running high, they have sex or rub their genitals together and everything’s just peachy. But bonobos do fight and they do form coalitions to support one another in aggressive interactions. By only looking to chimpanzees for understanding human aggression, we may be missing important evidence from bonobo conflicts.
A coalition is an alliance in which one individual is supported in an aggressive encounter by one or more other individuals. In chimpanzees, we know that males form coalitions that help win aggressive contests, thereby increasing rank and reproductive success1. Bonobos also form coalitions, but they look a little different. A recent study on wild bonobos at Wamba, Democratic Republic of the Congo, showed that female bonobos form coalitions to support other females. Females supported other females significantly more than males supported males or females and males supported each other.
These female-female coalitions were always directed against males, often after a male had behaved aggressively towards a female. Females never directed coalitions against another female. Most coalitions just involved chasing the male away, but 20% were physical attacks – during one such attack, the male was injured and lost the tip of one of his toes. The video below shows a particularly brutal attack on an adolescent male, who (as far as we could tell during our observation) was just in the wrong place at the wrong time.
When female bonobos form coalitions against a male (or males) they win 100% of the time. That success rate is so impressive that it’s almost no wonder they form coalitions. They can’t fail. But why would you help another bonobo? One hypothesis was that a bonobo should support close friends (as measured by proximity, grooming, genito-genital rubbing). But that’s not what the researchers found. Who supported whom was predicted best by age: old females support young females, and there is no reciprocity.
Why would old females help out younger females? Perhaps it’s a counter strategy against male harassment. Whenever a male starts to become more aggressive and disruptive, the females take him down a notch to the benefit of everyone. Rather than affiliative behaviours (like grooming and genito-genital rubbing) working towards creating coalitions, it might actually be that coalitions allow bonobo females to be more social and central to the group. They then need to put up with other females, and so the affiliative behaviours help to promote tolerance.
This is a guest post written by Kirsty Graham. She is a PhD student at the University of St Andrews, where she studies gestural communication in bonobos. Follow her on Twitter at @kirstyegraham.
1 – Male Chimpanzees Choose Their Allies Carefully
2 – Nahoko Tokuyama, Takeshi Furuichi
Do Friends Help Each Other? Patterns of Female Coalition Formation in Wild Bonobos at Wamba