Under the independence constitution adopted in 1979 and effective in 1980, Vanuatu is an independent republic within the Commonwealth of Nations. The head of state is the president (Fr. John Bani since March 1999); the head of government is the prime minister (Edward Natapei since April 2001). The unicameral legislature consists of fifty-two members (thirty-nine before 1987, and fifty before 1998) elected by universal adult suffrage to four-year terms. The cabinet is responsible to parliament, and the president is chosen by an electoral college for a five-year term. The electoral system includes a degree of proportional representation. A Council of Chiefs chosen by their peers in the chiefs' district councils advises the government on the protection of Vanuatuan languages and culture.