![enter image description here][1] Across the world religious people have more children than their secular counterparts. Offspring number, in modern environments, is inversely related to child success, yet children born to religious parents often flourish. Currently we have little understanding of how religion impacts the number of children people have or their children’s outcomes, and why these dynamics vary across religious groups. Moreover, processes of modernization greatly affect fertility, but it is unclear how these processes of social change interact with religion’s influence on reproductive decision-making and child success. These issues are of critical importance because they can inform understandings of how religion impacts core biological processes, and how these effects are altered by recent and broad social changes. Our project, funded by the [John Templeton Foundation][2], will systematically test hypotheses about the evolutionary dynamics of religion, family size and child success. This research uses data collected from 6,080 participants representing six religions, on three continents, in five societies with differing degrees of modernization, and on existing datasets from around the world, efficiently investigating questions of wide social significance at a global scale. This research will usher in a new scholarly field focused on the evolutionary demography of religion. This OSF project page contains pre-registrations, data and code for each of our studies. ---------- *Image: [Mormon family (1980) Linda Bartlett (Photographer)][3]* [1]: https://upload.wikimedia.org/wikipedia/commons/thumb/5/52/Children_playing.jpg/640px-Children_playing.jpg [2]: https://www.templeton.org/ [3]: https://commons.wikimedia.org/wiki/File:Children_playing.jpg