In "Bowling Alone," Robert Putnam explored America's burgeoning trend of social isolation. Now Putnam (with co-author David Campbell) meticulously examines American religion. The authors identify a widening political polarization between the religious and the nonreligious. Abortion and homosexuality have been especially divisive: 65 percent "of the least religious Americans" support a woman's unfettered right to choose an abortion, the authors note, while "only 13 percent of the most religious" agree; 90 percent of religious Americans believe "homosexual activity is always wrong," while only 20 percent of secular Americans agree.

We arrived at this religious-political divide in two steps: "Liberal sexual morality [of the 1960s] provoked some Americans to assert conservative religious beliefs," the authors write, "and then conservative sexual morality [of the 1980s] provoked other Americans to assert secular beliefs." Today, the Republican Party is the home of most religious Americans. But things may be changing. The authors point to a greater acceptance of diversity among religious groups. In addition, more Democrats are adopting "religious rhetoric and symbolism to neutralize the Republican advantage."

Much of the book's data are eye-opening. An influx of Latinos, for example, is pushing the Catholic Church in a more socially conservative direction. The data also indicate that religious people are generally more civic-minded, and more satisfied with their lives. The authors end on an optimistic note: the "mixing, mingling, and marrying" among differing religious groups, they say, has "kept America's religious melting pot from boiling over."