"The long duration of a belief, he thought, is at least proof of an adaption in it to some portion or other of the human mind; and if, on digging down to the root, we do not find, as is generally the case, some truth, we shall find some natural want or requirement of human nature which the doctrine in question is fitted to satisfy: among which wants the instincts of selfishness and of credulity have a place, but by no means an exclusive one."