WASHINGTON – There are plenty of interesting nuggets in the latest survey of Americans and religious faith by the Pew Research Center.

One that caught my eye: the stark differences in fertility rates between members of various religious traditions.

According to Pew’s data, the average Mormon can expect to make 3.4 babies in his or her lifetime. Jews, Catholics and most flavors of Protestantism have fertility rates ranging from 2 to 2.5. At the low end of the baby-making spectrum you’ve got atheists, with 1.6 kids, and agnostics, who average only 1.3.

On the face of it, this flies against the study’s main finding: If atheists and agnostics are having so few kids, how are their numbers increasing? The answer is many of the religiously unaffiliated are not born, but made: Many Americans are leaving their faiths and not picking up a new one.

“Nearly one-in-five American adults (18 percent) were raised in a religion and are now unaffiliated, compared with just 4 percent who have moved in the other direction,” Pew’s researchers write. “In other words, for every person who has left the unaffiliated and now identifies with a religious group more than four people have joined the ranks of the religious ‘nones.’”

It turns out that “none of the above” is winning the battle for hearts, minds and souls. But this doesn’t mean that Americans are renouncing faith completely and becoming diehard atheists. Indeed, while 22.8 percent of Americans say they are unaffiliated with any faith, only 3.1 percent identify as atheists. And 8.8 percent of Americans say they are unaffiliated, but also say that religion is very important in their lives.

The unaffiliated share of the North American population is projected to grow over the next 40 years, according to an earlier Pew report. But the unaffiliated share of the global population will decline, partially because of those low fertility numbers.