A sangoma is a practitioner of herbal medicine, divination and counselling in traditional Nguni (Zulu, Xhosa, Ndebele and Swazi) societies of Southern Africa (effectively an African shaman). The philosophy is based on a belief in ancestral spirits. Both men and women can be called by the ancestors (a consequence of refusing the calling is usually ongoing physical or mental illness[citation needed]) though sangomas are usually female. Historically the sangoma role has been the preserve of the black, indigenous peoples of Africa, but post-Apartheid white South Africans have also entered the profession - John Lockley is reputedly one of the first white men in recent history to become a fully initiated Xhosa sangoma. A trainee sangoma (or twaza) trains under another sangoma, usually for a period of years, usually performing humbling service in the community. At times in the training, and for the graduation, a ritual sacrifice of an animal is performed (usually a chicken, a goat or a cow). The spilling of this blood is meant to seal the bond between the ancestors and the sangoma.