Until I644 the legislature [in Massachusetts] was unicameral although the assistants had what was called a ” negative voice ” in spite of the fact that they constituted a minority of the Court. Being better educated and accustomed to leadership they ordinarily monopolised the debates. The irritation which resulted came to a head in I644 following a bitter series of suits between the Goodwife Sherman, a poor widow of Boston, and one Robert Keayne, a merchant of that city, who had killed her sow when it trespassed upon his property. Three times the suit came before the General Court; three times the deputies sided with the widow and the assistants with the merchant. The deputies denied the right of the ” negative voice ” ; the clergy and many of the colonists took sides in the dispute. The upshot was vindication of the ” negative voice ” and separation into two houses of legislation. Such is the origin of the bicameral system in America!
In short, Americans have a pig to thank for forever having two houses of Congress [OK, may be eventually the South would have adopted the UK system with an upper house to protect southern aristocratic interests….]
Peverill Squire confirms this story in his excellent book on the Evolution of American Legislatures (1619-2009)