When Aurora Turk was growing up in Mexico City, being Catholic was a given. “It was taught to me by the nuns at school and my mother at home,” she recalled. “My whole world was Catholic.”

But Turk’s adult life has been marked by religious exploration. Married to a Brooklyn-born Jew, the 38-year-old mother now follows the teachings of Paramahansa Yogananda, an Indian spiritual teacher; she and her husband plan to raise their infant son in the Self-Realization Fellowship, a group founded by Yogananda, at their home in Springfield, Va.

While Turk’s story seems unique, her experience of switching religious identities is a common one for many Americans. According to experts who study the phenomenon, believers are exercising their freedom of choice more than ever before.

Sixteen percent of Americans have switched their religious identities at some point in their lives, according to the 2001 American Religious Identification Survey, one of the largest studies of its kind.

“People are making more choices in everything, from lifestyle to sexual identity. It’s not surprising if they are making more choices in religion,” said Peter Berger, professor of sociology and theology at Boston University.

In other words, Berger says, the era when religion was determined solely by accident of birth is over.

Barry Kosmin, co-author of the 2006 book “Religion in a Free Market: Religious and Non-Religious Americans,” which is based on the 2001 survey data, said “more switching is to be expected.”

“Family and ethnic loyalties _ the old glue that maintained inter-generational religious identification _ has weakened,” he said. In addition to moving more frequently, Americans are also more likely to be “searching” for religious truth, often outside their own traditions, wrote Kosmin, who directs the Institute for the Study of Secularism in Society and Culture at Trinity College in Hartford, Conn.

The 2001 study showed clear winners and losers in the competition to attract and retain members: Twice as many Americans left Catholicism as joined the faith, while evangelical Christianity registered a net gain, with more than three times as many people joining than leaving.

The biggest change, however, was registered among Americans who said they had no religious identity at all, increasing from 8 percent of the U.S. population in 1990 to 14 percent in 2001.

For Cindy Belsky, the journey has been in the opposite direction, from the “California spirituality” of her parents to a family-centered version of Conservative Judaism.

“We didn’t practice any formal religion when I was growing up, unless you count the time when the whole family learned Transcendental Meditation,” said Belsky, whose mother was Presbyterian and father was Lutheran.

When Belsky married her husband, who grew up in an observant Jewish household in Miami, she agreed to raise their children in her husband’s faith. When her oldest son, Daniel, started preschool at a nearby Conservative synagogue, Belsky was surprised by what she found.

“I walked into the preschool and was enveloped in warmth. I felt so at home,” she recalled. Today, Belsky, 43, teaches at the preschool, and every Friday night she gathers her husband and five children to light Shabbat candles and sing Hebrew prayers at their home in Chantilly, Va. She said she is seriously considering converting to the faith

“My own religious background was so slippery, not concrete. I want to belong to the community, and I want that sense of identity for my children,” Belsky said.

While religious switching may bring satisfaction to individual seekers, the phenomenon can be unnerving for religious leaders, who are vying for “customers” ever more aware of new options, according to Kosmin.

“We have a supply-side religious market with more competing firms each year,” he wrote in an e-mail interview. Megachurches are successful in part because they actively reach out to “potential” members, of which there are many in high-mobility suburbs and exurbs, Kosmin wrote.

But success in attracting new members doesn’t necessarily translate into success at keeping them, according to Daniel Olson, a sociologist at Indiana University South Bend who studies religious competition.

“There is a strong relationship between rates of leaving and rates of joining, both for congregations and whole denominations,” Olson wrote in an e-mail response to questions. The 2001 survey found, for example, that while the Mormons welcomed a relatively large number of converts, an equal number left the faith. Jehovah’s Witnesses and Buddhists displayed similarly high levels of turnover.

Surprisingly, Olson noted, smaller religious groups are better at recruiting new members. Most switching happens through social relationships, like marriage and friendship, explained Olson, and members of a small religious group are more likely to have lots of relationships with non-members, whom they are able to pull into the faith.

Carl Blizzard, pastor of the Abundant Life United Pentecostal Church in Albert Lea, Minn., said his church is small, with only 300 active members _ 90 percent of whom came to Pentecostalism from Lutheran, Catholic and even Muslim backgrounds.

“People usually come in first because they are invited by a family member. The church is growing because of personal testimony,” said Blizzard, son of a Pentecostal preacher.

But even for Blizzard, Pentecostalism was not a given. In his early 20s, he visited Baptist, Methodist and Catholic churches. “I wanted to see if what I had been taught (growing up) was true. I found that the spirit is alive in a Pentecostal church,” he said.

Berger, the Boston University sociology professor, spoke in December at a Key West, Fla., conference sponsored by the Washington-based Pew Forum on Religion & Public Life, and argued that “modernity in its essence means an enormous change in the human condition, from fate to choice.” Encountering other people’s religious beliefs _ and perhaps being persuaded by them _ is “an inevitable part of modernity.”

Berger cited the example of his 6-year-old granddaughter _ born to a Protestant father and a Hindu mother _ who holds fascinating theological conversations with a girl across the street, whose parents are missionaries for the group Jews for Jesus.

“I would say interreligious communication by 6-year-old little girls is more significant than interfaith committees set up by the Vatican,” he said in Key West, “because there are many more little girls than there are theology professors.”

RNS-AMERICAN-FAITH is an occasional feature that spotlights the changes and currents flowing through American congregations and faith communities. The stories in AMERICAN FAITH depict a ground-level view of what faith looks like in America amid changing demographics, worship styles and beliefs. We hope it offers a view of how faith is expressed and practiced by real people in real places.