The Polahi nomadic tribe living in isolation in the forest of Indonesia's Gorontalo province practices incest, permitting relationships between father and daughter or mother and son, a report said in Jakarta on Wednesday.
"There is no other choice. In villages, there are many people but here, there is only us, therefore we can marry between people of the same blood," Mama Tanio, a matriach of the tribe, told the Kompas online news portal.
The report gave no population count of the Polahi community, but said that they were a nomadic forest tribe with no education and tended to shun contact with the outside world.
The tribe roams the thick forest of Humohulo in the Boliyohuto mountain range of Boalemo district in Gorontalo on Sulawesi island.
It is considered normal if a father marries his daughter or a son marries his mother.
The former head of the tribe, Baba Manio, who died in April, had two wives, Mama Tanio and Hasimah.
Babuta, the son of Mama Tanio and Baba Manio, replaced his father. Babuta is married to his sister Lailya, who is the daughter of Baba Manio and Hasimah.
Marriage rites are also simple, with the couple taken to a river and water thrown on both of them while mantras are read out.
Kompas online quoted photographer Ebbi Vebri Adrian, who often has contact with the tribe, as saying that despite their intermarriage, the tribe did not appear to suffer from the genetic deterioration usually associated with the practice.
"What is strange is that none of their descendents appeared handicapped, as is usual with intermarriages," he said.