In part of a larger study called “Fertility of American Women: June 1992,” the Census statisticians compared rates of childbearing among single women in 1982 and 1992. None had ever been married, but some had live-in partners. Anne Lamott, 39, of San Rafael, Calif., is the author of “Operating Instructions,” a journal of her first year as a single mother. Her son, Sam, will be 4 next month. “Ideally, Sam would have a father who adored me and adored him,” she says, “but we don’t have that.” When Lamott became pregnant by a man she didn’t feel very close to, she decided to have the baby on her own. “I always wanted to have a child,” she says. “I knew so many women who were waiting for that Alan Alda type to come along, and wanting a committed relationship. And they were waiting and waiting.”

The rise in out-of-wedlock births across racial groups and educational levels has prompted a search for new explanations. “Whatever is driving single motherhood, we can’t look at it as a specific product of poverty, race or education,” says Roderick Harrison, chief of the Racial Statistics branch of the Census Bureau. “The contributing factors have more to do with a shift in family structure and the place of marriage.”

Both men and women have been to some extent retreating from marriage-or at least postponing it. At the same time, middle-class social acceptance of unwed motherhood has grown, and women’s earning power has continued to climb. They’re also getting pickier. “College women today have much higher standards for their spouses than their mothers did,” says Andrew Hacker, who wrote “Two Nations: Black and White, Separate, Hostile and Unequal” and teaches political science at Queens College in New York. “This study is a harbinger of something important: an increasing number of women who are smart and educated are finding that there aren’t enough men who are up to their standards.” Rather than setting their husband sights lower, more of these late-20th-century women are chosing the challenge of becoming mothers without being wives.