Book excerpt: From the end of the New Deal until quite recently, the U.S. House of Representatives was dominated by a conservative coalition that thwarted the Democratic majority and prevented the enactment of measures proposed by a succession of liberal Presidents. Today Presidents aren't necessarily liberal and the House of Representatives is not necessarily the graveyard of presidential proposals. What happened? Congress evolved. It all began with airconditioning. In this entertaining tale of one of our most august institutions, Nelson Polsby describes how the Democratic majority finally succeeded in overcoming the conservative coalition, changing the House. The evolution required among other things, the disappearance of Dixiecrats from the House Democratic caucus. Dixiecrats were replaced by the rise of the Republican party in the south. The Republican party in southern states was strengthened by an influx of migrants from the north, who came south to settle after the introduction of residential air conditioning, which made the climate more tolerable to Northerners. This evolutionary process led to the House's liberalization and concluded with the House's later transformation into an arena of sharp partisanship, visible among both Democrats and Republicans. A fascinating read by one of our most influential political scientists, How Congress Evolves breathes new life into the dusty corners of institutional history, and offers a unique explanation for important transformations in the congressional environment.