Can an explanation of a set of beliefs cast doubt on the things believed? In particular, can an evolutionary explanation of religious beliefs call the contents of those beliefs into question? Yes - under certain circumstances. I distinguish between natural histories of beliefs and genealogies. A natural history of a set of beliefs is an explanation that puts them down to naturalistic causes. (I try to give an account of natural explanations which favors a certain kind of ‘methodological atheism’ without begging any crucial questions against theists.) A genealogy is an explanation which somehow subverts the claims believed, usually by putting down the beliefs to unreliable causal mechanisms. Some genealogies are natural histories, such as Aquinas’s explanation of the prevalence of Islam and Gibbon’s explanation of the prevalence of Christianity. But not all genealogies are natural histories and not all natural histories are genealogies: witness the Primitive Christians’ explanation of the prevalence of Paganism which relies crucially on supernatural agencies and Hume’s explanation of our moral beliefs which defines moral truth in terms of the idealized outputs of our natural belief-forming mechanisms. However both believers and non-believers postulate a natural propensity of to devotion on the part of human beings a ‘sensus divinitatis’ which often results in false positives and is therefore unreliable. Thus the evolutionary explanation of this propensity does not add much to the skeptical case against religion. I conclude by arguing, as against Plantinga that since on his own showing our sensus divinitatis often malfunctions under optimum conditions, its unreliability constitutes a defeater for the claim that Christian beliefs are properly basic.