> While religiously unaffiliated people currently make up 16% of the global population, only an estimated 10% of the world’s newborns between 2010 and 2015 were born to religiously unaffiliated mothers. This dearth of newborns among the unaffiliated helps explain why religious “nones” (including people who identity as atheist or agnostic, as well as those who have no particular religion) are projected to decline as a share of the world’s population in the coming decades.

https://www.pewforum.org/2017/04/05/the-changing-global-reli...