I found Stewart-Williams’s book most interesting as a lucid statement of a kind of ‘commonsense naturalism’ — the set of metaphysical, methaethical and ethical views that seem to be attractive to educated and sophisticated atheists. These appear to include the claims that free will is an illusion, life is meaningless, morality is a myth and ultimately based on our subjective attitudes, and that the only thing that morally matters is suffering (and presumably pleasure). While not an incoherent set of views, and while I can see how it can be an attractive package to a certain kind of person, it is in some ways a peculiar list. In particular, as Bernard Williams pointed out, it is actually fairly easy to reject utilitarianism if one takes morality to be ultimately based on nothing more than our subjective commitments. Stewart-Williams is careful enough to distinguish a range of theist views in the first part of the book and tries to assess how each is affected by the truth of evolutionary theory. It is unfortunate that in the rest of the book he presents such a narrow picture of the ethical views that are left on the table once we accept evolutionary theory, given that evolutionary theory — or rather, naturalism — is perfectly compatible with a far broader range of metaethical and normative options.
This book is clearly written and vigorously argued. It covers a lot of ground, but it is not philosophically deep or especially original. The arguments against God’s existence in its first part are unlikely to impress theists philosophers, who will (perhaps rightly) feel that Stewart-Williams simply ignores the most important theist moves and arguments of recent decades. The discussion of morality, while lucid, is largely derived from Ruse, Joyce, Rachels and Singer — authors that are already rather accessible. This book would be fine for an introductory undergraduate course. The discussion is a bit more focused and systematic than recent New Atheist books, but if I had to choose an introductory book for an undergraduate course, I’d probably prefer Dawkins and Dennett.