抄録
Numerous comparative studies have shown that Pan paniscus exhibits many socio-sexual characteristics which are distinct from those of Pan troglodytes. These characteristics can be considered as successful counter-strategies against potential infanticide by males.
1) Female P. paniscus show longer maximal tumescence period per cycle, larger number of cycles during pregnancy, earlier resumption of a cycle after giving birth, than those of P. troglodytes. All of these increase a female's sexual receptivity which help to mitigate male-male sexual competition, the principal motivation for infanticide.
2) Female P. paniscus appear to form a sort of alliance against males: they are more closely associate with each other than males do, both in the formation of parties and spatial distribution, and are cooperative in agonistic interactions with males. They prevent males from establishing a coalition by assisting young males to gain higher ranking positions, and also by maintaining a close association with their sons even after they mature. Thus, females, in spite of their physical inferiority to males, attain equal or even higher social positions than males. This makes it difficult for males to behave violently towards infants.
3) Female P. paniscus take the initiative in peaceful contact with different groups. They mate more frequently with males from different groups than with males of their own group during intergroup encounters. Intergroup copulations, together with obscured ovulation through prolonged estrus, make it difficult for males to determine paternity. This extreme confusion of paternity is considered to be a powerful deterrence to infant-killing by males of both the same group and between different groups.
