This is a nice little book, very easy to read. While I was familiar with most of the factual contents, there are a few remarkable insights and claims that feel plausible. The basic tenets are based on archeological data on the size of the frontal lobes and the idea that the frontal lobe size has rough correspondence with the ability to understand recursive intentions. For example, while current humans seem to understand four or five orders of intentionality (sometimes six), chimps seem to be on the brink of understanding second order intentionality. That is, while we can understand that Alice believes that Bob thinks that Carol wants David to supposed that Eve imagines..., chimps can barely understand that Alice believes that Bob thinks.... Consequently, much of the evolutionary pressure behind brain growth seems to have been the ability to cope with in larger social groups. Another basic tenet is that language seems to have developed as a form of social grooming, and that is primary purpose is to act as a social cohesion force.
The chapter about religion (Chapter 7, last one) was perhaps to most interesting to me. Again, nothing very new, but nice insights, especially about the role of religion in allowing even larger societies to be built than with just language.