E.O. Wilson in Consilience: The Unity of Knowledge:

If the religious mythos did not exist in a culture, it would be quickly invented, and in fact it has been everywhere, thousands of times through history.  Such inevitability is the mark of instinctual behavior in any species.  That is, even when learned, it is guided toward certain states by emotion-driven rules of mental development.  To call religion instinctive is not to suppose any particular part of its mythos is untrue, only that its sources run deeper than ordinary habit and are in fact hereditary, urged into birth through biases in mental development encoded in the genes.