The meaning and context of gender is contested even in the 21st century. No generalizations about gender are applicable through time or across space. Even where gender roles are defined by particular cultural norms, they are not static, and an individual may pass through several gendered social transformations in a lifetime. Sub-Saharan African rites of passage into adulthood are sometimes marked by gender-specific physical mutilations such as circumcision, dental modification or scarification, together with other forms of symbolic marking that invariably adopt a binary gender system as the norm. The initiations are largely designed to instruct initiates about behavior appropriate for men and women of reproductive age belonging to a specific community. Some aspects of initiation rites may be detected archaeologically through skeletal alterations, rock art motifs, and props such as scarified dolls. Concepts of gender are also connected to the last rite of passage: burial. Through this, people gain access to the ancestral world. In some parts of Africa such as Mali, men and women are buried with the artifacts they owned in life, while in Ethiopia, stelae mark the gender of the deceased. Elsewhere, as in the Stone Age of southern Africa, gender-undifferentiated grave goods are placed with men, women, and children, suggesting a genderless ancestral world. Gender roles can be identified in some archaeological sites in parts of Africa, and these roles sometimes appear to have altered through time. Gender roles changed with environmental shifts, and certain tasks such as big-game hunting disappeared as a result. In other cases, gender roles were revised because of social pressures imposed on specific communities.