"I didn't know it back then," Ethan Watters writes of his post-college move to San Francisco, "but I was a harbinger of a massive trend." The trend under discussion is one that will surely be familiar to many readers: the tendency of college-educated young people to delay marriage, often for a decade or more, in favor of extended sojourns in the company of a group of fiercely loyal friends located in the same big city—an "urban tribe." Like so many contemporary nonfiction books, Urban Tribes consists of a decent magazine piece that has been force-fed enough survey results and statistics and "research" to justify two hard covers and a twenty-four-dollar price tag. When Watters gets bogged down in theories of group behavior and social evolution, the book plummets. But when he writes anecdotally (the best parts of Urban Tribes concern the difficulty of teasing an entire "trend book" out of a thousand-word essay), he displays a light touch and is often entertaining. We learn a good deal about Watters's own tribe, busy little beavers who are forever throwing theme parties, chewing over the state of gender relations, and whipping themselves into creative frenzies (when one friend gets a glass-blowing commission, a second makes a documentary film about it, a third milks it for a magazine article, and a fourth gets a part-time job assisting in the blower's studio). The book's outlook is sunny in the extreme, and its target audience—and mothers of same—will probably be cheered to learn that sociologists predict that most members of urban tribes will eventually settle down in conventional marriages. Watters has much to say about the opinions and beliefs of his generation, and I assumed I was getting news from the front about what kids are up to these days; imagine my surprise when I learned that the author is almost forty. In this new light I began to suspect that Watters—with his pack of irrepressible housemates and his fondness for making new friends by wandering around the Burning Man festival with an open tub of red licorice—might be representative less of a striking new social trend than of arrested development. But by book's end he has wrestled his commitment "issues" to the ground, made a partial break with his buddies, and gotten married to a young psychiatrist whom he met when she showed up at a tribe party dressed as Betty Rubble. In fact, by the epilogue it's dateline Hawaii, where he is on his honeymoon—soft breezes blowing into the connubial bedchamber, his bride frolicking on the beach below—and putting in a wholehearted endorsement for the grand old institution of marriage. I got the distinct feeling that a second trend book may soon be upon us; awash in the self-satisfaction that so often gathers around a man on his honeymoon, he ruminates, "I suspect that I am again a bellwether."