Other questions that have been considered in the study of primate aggression, including in humans, is how aggression affects the organization of a group, what costs are incurred by aggression, and why some primates avoid aggressive behavior. For example, bonobo chimpanzee groups are known for low levels of aggression within a partially matriarchal society. Captive animals including primates may show abnormal levels of social aggression and self-harm that are related to aspects of the physical or social environment; this depends on the species and individual factors such as gender, age and background (e.g. raised wild or captive).