Conclusion

Sexual behaviors such as copulation, GG rubbing, and prolonged sexual receptivity, which are unique to bonobos, have been thought to be closely linked to the female’s high social status and the peaceful nature of bonobo society. However, their physiological basis is not well understood. Nevertheless, in recent years, as methods for analyzing sex hormone dynamics using noninvasive samples have been developed, we have gradually come to understand the sex hormone dynamics in female bonobos. These analyses reveal that the early resumption of sexual receptivity after parturition occurs before the mother is ready for the next conception. Prolonged sexual receptivity could be attributed to two reasons: reduced OSR and enhanced affiliative relationships between females.