The House of Commons is the lower house of the Parliament of the United Kingdom. Parliament also includes the Sovereign and the upper house, the House of Lords; the House of Commons is the dominant branch. The House of Commons is a democratically elected body, consisting of 646 members, who are known as "Members of Parliament" or MPs. Members are elected by the first-past-the-post system of election, holding office until Parliament is dissolved (a maximum of five years). Each member is elected by, and represents, an electoral district known as a constituency. The House of Commons is the source of the vast majority of government ministers and every Prime Minister since 1902, with the very brief exception of Sir Alec Douglas-Home in 1963, has been drawn from it (Home did actually rule from the House of Commons, however, taking a seat in the House shortly after being chosen as Prime Minister). The House of Commons evolved at some point during the 14th century and has been in continuous existence since. The House of Commons (the "lower house") was once far less powerful than the House of Lords (the "upper house"), but is now by far the dominant branch of Parliament. The House of Commons' legislative powers exceed those of the House of Lords; under the Parliament Act 1911, the Lords' power to reject most bills was reduced to a mere delaying power. Moreover, the Government of the United Kingdom is answerable to the House of Commons; the Prime Minister stays in office only as long as he or she retains the support of the lower house.