People often talk about voluntary religious conversion as if it were motivated by spiritual zeal. But in her new book, historian Susan Jacoby argues that the past tells a different story. In the early 20th century, it was common for Jews, like Jacoby’s great-uncle, to embrace Christianity to improve their social class and career prospects. In the years that followed, more people started converting for love–a man adopting his wife’s religion to please her family, for example, or a couple taking up a new faith entirely before or after saying “I do.” (One study estimates the latter comprises 15% of all conversions.) And at times, Jacoby writes, switching faiths could appear politically shrewd, as when Newt Gingrich, raised Lutheran, became a Southern Baptist years before launching his first campaign in Georgia. “I would never deny that an intense emotional desire to believe in something true … motivates many conversions,” writes Jacoby, who considers herself an atheist. “But so do other, more earthly needs and longings.”
This appears in the February 22, 2016 issue of TIME.