"Punctuating a fundamental change in American family life, married couples with children now occupy fewer than one in every four households - a share that has been slashed in half since 1960 and is the lowest ever recorded by the census.

"As marriage with children becomes an exception rather than the norm, social scientists say it is also becoming the self-selected province of the college-educated and the affluent. The working class and the poor, meanwhile, increasingly steer away from marriage, while living together and bearing children out of wedlock."