Early popes? Peter was appointed by Christ; he appointed his successor, etc. There have been 110 papal elections that have produced popes currently recognized by the Catholic Church as legitimate. There was no fixed process for papal succession before 1059 and popes were often selected with substantial secular involvement, if not outright appointment. Since the promulgation of In nomine Domini (1059), however, suffrage has been limited to the College of Cardinals. Vacancies between popes, and most immediately the interregnum of 1268-1271, prompted the Second Council of Lyons to decree in 1274 that the electors should be locked in seclusion cum clave (Latin for "with a key"), and not permitted to leave until a new Bishop of Rome had been elected. Conclaves are now held in the Sistine Chapel at the Vatican. In essence, the bishops are held hostage until they elect a new pope!
The last time a pope quit was almost 600 years ago. Gregory XII "left the papacy in 1415 to end what was known as the Western Schism among several competitors for the papacy," report The New York Times's Elisabetta Povoledo and Alan Cowell. The theory here is that if Benedict is retiring now, then it must mean there's something as big as that dividing the Church right now.