Some atheists have argued that children are naturally non-believers. Were it not for indoctrination at the hands of parents and clergy children would never pick up supernatural beliefs on their own and religion would wither and die. But a growing body of research in developmental psychology suggests just the opposite. Children have a natural inclination to believe in invisible, immortal, super-knowing agents who are responsible for design in the natural world. For this first part in a series on the evolved origins of religious belief the doubtcasters review two books (Justin Barrett's Born Believers and Jesse Berring's the Belief Instinct) which make the case that religious belief is not only natural--it is almost inevitable.