The behavior in which two or more individual organisms cooperate to attack the same individual is called "association attack".In general, "blood relations" are strongly related to the relationship between female animals, and especially in primate females, the association is basically formed by blood relations.On the other hand, it is known that females have weak social ties in species with paternal group morphology that are not related to each other, such as chimpanzees.

　Bonobos (Pan paniscus), an ape close to chimpanzees, also form a paternal group, and the females in the group are not related to each other.Nonetheless, bonobos show a rare relationship in which females form strong bonds and frequently make coalition attacks on males.Furthermore, it is known that the bonobo society is characterized by the fact that "female is dominant".Although female associations are considered important for maintaining this advantage, it has not been clarified by what criteria females actually form associations.

　The research group investigated this point in a group of wild bonobos living in the Luo Academic Reserve in the Democratic Republic of the Congo.As a result, it was found that all female coalition attacks targeted males, especially immediately after the males were attacked by females.It was also found that when forming an alliance, instead of selecting females with a strong affinity, the rule is that "older females help younger females attacked by males". rice field.It is disadvantageous for young females to take a one-on-one attack with males, but it is said that females were able to beat males 1% when they formed a coalition.

　The findings suggest that females cooperate in retaliation against male aggressive behavior to control male aggression and maintain female dominance as a whole.The mechanism by which female bonobos form an alliance is considered to be important in considering the evolution of social relationships between females in humans, who tend to have a strong tendency to disperse females.