The U.S. House of Representatives has grown in membership in its more than two centuries of history, from the sixty-five seats allocated in the original Constitution (Art. I, sec. 2, cl. 3) to a more than fi vefold increase (356 seats) a century later, following the 1890 census, to its present size of 435 seats—unchanged since the forty-seventh and forty-eighth states were admitted in 1912. In all its history, there have been only two mechanisms by which the membership of the House has been augmented: by the admission of new states, whose people thereby take on the character of a political unit amenable to representation in the House; or by the addition of new seats to be distributed proportionally among the existing states of the Union to refl ect population growth. both of these steps are of course accomplished by act of Congress....