Following on from his two other deservedly acclaimed preceding books, Mr Williams delves deeper into the origins of religion, the central message being that all religious activity stems from neurological activity in the brain. Ok, no arguement with that. He also draws fascinating parallels between medieval mysticism and the visions of the San bushmen. Terrific stuff, even though he then seems to postulate that virtually every deep religious experience or spiritual vision can be explained by a migraine attack. Not sure about that but it's a good challenge to wrestle with. What mars the book in my opinion is the relentless, almost suffocating attack on the Catholic church and the Bible. I can quite happily live without either so I have no axe to grind but the constant bile detracts from the rest of the book. I concede quite happily that any debate between science and religion has resulted in a retreat or reinterpretation on the part of religion. I wouldn't agree though that no useful material has ever resulted from the use of hallucinogenics. It's quite likely that the cave paintings Mr Williams admires so much were created or inspired in some part by magic mushrooms or cannabis rather than migraine. And as a child of the 60's much of the music I love seeped out from a drug-hazed creativity. And the assertion that no Shaman can make it rain or mend a broken leg is to my mind, pure, inexcusable ignorance. So - four stars rather than five only because of the caustic overspill that stains much of the book. Something or someone has rattled Mr Williams' cage and he obviously feels compelled to make a stand for science. I respect that, but his case is somewhat overstated and he's in danger of becoming pigeon-holed as just another atheist one trick pony a la the oft quoted but misunderstood Richard Dawkins. Otherwise a good, lucid read.You don't have to agree with a lot of the findings but I admire passion and intelligence - and a good arguement.