野生ボノボ(<i>Pan paniscus</i>)群における攻撃行動の意味

Bonobos were observed daily at the feeding site in the Wamba forest in Zaire from Dec. 20, 1979 to April 16, 1980. The unit group, Elanga group, consisted of 2 subgroups, and adults of each subgroup are divided into a male class and a female class. The male class of one of the subgroups was further divided into 2 classes, a central male class and a peripheral male class. Thus the adult members of the unit group were divided into 5 classes, 3 classes of adult males and 2 classes of adult females. The condition of the parties which came to the feeding site was described with regard to the participation of adult male classes in the party; each male class either arrived independently of the other male classes, or in combination with two or more classes.<br>Female bonobos conducted the “dragging branch display”, which occurred during the same period as “females'attacks against adult males”. Both behaviors occurred in a narrowly limited period within the whole study period. However, females did not direct their “dragging branch behavior” to adult males. Females avoid one to one confrontation with adult males. Females' “dragging branch behavior” has the characteristic of a display which facilitates the avoidance of one-to-one confrontations.<br>Males conducted both one-to-one directed and undirected “dragging branch behavior”. Subordinate males tended to direct their “dragging branch behavior” toward dominant males. The behavior has the characteristics of a “challenge behavior from subordinate against dominant males”, not the avoidance of direct confrontation. Most of the “dragging branch behavior” between males and females was directed from males to females. There was a strong tendency that bonobo males did not attack females of the same subgroup. These facts indicate that bonobo males were subordinate to females, and that males were challenging females.<br>“Directed running without dragging branch” was usually conducted by the dominant against the subordinate among males, indicating that the behavior is a dominant behavior. However, this behavior was conducted in both directions between males and females, showing unclear dominance.<br>Dominance among males seemed to be dually determined, one by interactions among males, and another by the influence of supports by females. Supports by females (involving mothers) were unstable depending on the changes of females'physiological conditions.<br>Though males did not attack females of the same subgroup, males attacked females of the other subgroup. Thus, when 2 subgroups came together, females' influence on males from different subgroups decreased. The encounter of different subgroups served to destroy the society based on mother-son bonds. This fact implies a different view from that in which females are seen to initiate fusion of groups at group encounters.<br>Since each of the behavior patterns, “females' attack against males” and “females'dragging branch display” occurred within a limited period, the cause which brought about these behaviors was sought in the interactions in the preceding period. An attempt was made to find a chain of causes and effects between preceding and subsequent periods. This method introduces stories among the consecutively occurring social events. This method produces “stories” from consecutively occurring social events. This method may substantiate to some extent the anthropomorphic expressions which usually have been used in literature written in Japanese dealing with social dynamics of primates.