A kaumātua is a respected tribal elder of either sex in a Māori community who has been involved with their whānau for a number of years. They are appointed by their people who believe the chosen elders have the capacity to teach and guide both current and future generations. Kaumātua have good knowledge of Māori tikanga, language and history; and their contribution ensures that the mana of the whānau, hapū and iwi are maintained. Barlow (1994) refers to kaumātua as being the "keepers of knowledge and traditions of the family, sub-tribe and tribe". Although the term kaumātua is widely used to refer to all elders, male kaumātua are more correctly called koroua or koro, and female elders are called kuia. The word kaumātua comes from kau, meaning alone, without or none, and mātua, meaning parents; thus, kaumātua literally means "no parents" and reflects how the parents of older generations have passed on. Kaumātua never self-proclaim their elder status, as the rules of mana prohibit this; instead the people acknowledge an elder's status as kaumātua. Kaumātua comport themselves with humility, honesty, and integrity, and typically possess deep knowledge of a particular subject such as whakapapa or tikanga, and know people who have expertise in other fields. In the past, kaumātua were believed to be "the reincarnation of a person who had acquired a supernatural or godly status after death, and who had become the protector of the family". These supernatural powers allowed the reincarnated spirits to return to earth to provide influential guidance to the remaining family. It was believed that these powers allowed the kaumātua transform themselves into birds, fish and insects. Elders of the tribe made reference to these transformed states when predicting the future and fortunes of the tribe. Additionally, along with leadership and guidance of family and marae, many kaumātua exert a protective influence over the seas, rivers, lands and forests. Kaumātua are essential to any Māori community as well as health organisations which have affiliations with Māori.