I haven't read The God Delusion so I don't know. But just the fact that people tend to believe in a fictional God doesn't necessarily mean there's an evolutionary advantage. It could easily be a secondary artifact of our evolution, like many things that people look for evolutionary-psychological reasons for. Or it could be that it's a distortion of something we were all once very much connected to. That would make belief in God an attribute of life itself (as in consciousness/awareness/spirit), which exists prior to and is more fundamental than biological life, like many other things that people scientistically look for evolutionary reasons for.