Mr. Putnam spoke about his book Bowling Alone: The Collapse and Revival of American Community, published by Simon and Schuster. The book examines the ways in which Americans gather in social groups and suggests that social interaction is less prevalent than ever before. Mr. Putnam said that league bowling is characteristic of this social change in which Americans have become increasingly disconnected from family, neighbors and social structures such as the PTA, church clubs or sports leagures.