In Japan, ritual uncleanliness resulted from contact with unsanitary things, human blood, human or animal death, natural disasters, disturbed life in human society, and incest or bestiality. For example, sumo wrestlers claim their ring to be part of sacred Shinto rituals of the sport and no women are permitted to enter it as their touch would soil it. In certain Chinese sub-cultures death pollution is a major concern, as with many South American Indians where mourners must undergo purification after funerals. In its relationship to the system of taboos prevalent in tribal cultures, the condition is of widespread concern.