For Dennett, to prove the biological origin of belief in God is to show its irrationality, to break its spell. But of course it is a necessary part of the argument that all possible human beliefs, including belief in evolution, must be explicable in precisely the same way; or else why single out religion for this treatment? Either we test ideas according to arguments in their favor, independent of their origins, thus making the argument from evolution irrelevant, or all possible beliefs come under the same suspicion of being only evolutionary adaptations—and thus biologically contingent rather than true or false. We find ourselves facing a version of the paradox of the Cretan liar: all beliefs, including this one, are the products of evolution, and all beliefs that are products of evolution cannot be known to be true.

One striking aspect of Dennett’s book is his failure to avoid the language of purpose, intention, and ontological moral evaluation, despite his fierce opposition to teleological views of existence: the coyote’s “methods of locomotion have been ruthlessly optimized for efficiency.” Or: “The stinginess of Nature can be seen everywhere we look.” Or again: “This is a good example of Mother Nature’s stinginess in the final accounting combined with absurd profligacy in the methods.” I could go on, but I hope the point is clear. (And Dennett is not alone in this difficulty: Michel Onfray’s Atheist Manifesto, so rich in errors and inexactitudes that it would take a book as long as his to correct them, says on its second page that religion prevents mankind from facing up to “reality in all its naked cruelty.” But how can reality have any moral quality without having an immanent or transcendent purpose?)