In Religion Explained, Boyer attempts what no one else (to my knowledged) has: to present a comprehensive scientific explanation for religion. To undertake such a daunting task, Boyer employees numerous behavioral science disciplines, including evolutionary psychology, experimental social psychology, anthropology, sociology, and archeology just to mention a few. Early on, he debunks common and prevalent explanations for religion (many of which I subscribed to before reading this book) as facile and scientifically invalid.
Using Evolutionary Psychology as a foundation, Boyer describes how specific brain structures evolved to perform specific inferences related to basic survival (especially relevant are predatory and contagion inference) and the numerous inter-related systems used for conspecific interaction and cooperation. [It is especially important to understand that most inferences operate apart from conscious perception.] After comprehensive discussion of the multitudinous, interactive inference systems, Boyer describes how they collectively work to form religion. He explains that most varieties religious concepts (gods, spirits and other supernatural agents and their abilities; morality; death issues, etc.) and public behavior (rituals and prayer, religious-associated violence) can be explained in terms of these inference systems.
While he presents an effective argument for most aspects of religion, Boyer admits that a convincing scientific explanation for some forms of ritualistic behavior is elusive. He offers detailed speculation regarding the etiology of rituals, but admits the research at this time is inconclusive and mostly speculative. He compares rituals to similar non-religious activity, such as the compulsions associated with Obsessive-Compulsive Disorder, but this is only a plausible partial explanation because religious rituals exhibit distinct differences. OCD compulsions are undesired and cause psychological distress in the participant, while participation in rituals is usually voluntary and isn't inherently distressing to the participants (though sometimes it can be). Also, rituals normally occur in a culturally-related social context while compulsions are a repetitive form of individual behavior.
The only element of Religion Explained that was a little disappointing to me was the cursory discussion of secularism. Boyer explains that religion (in one form or another) is conducive to normal human brain functions. This of course evokes discussion of why some people are completely irreligious. Boyer only touches on this issue briefly and in a manner which seems a little obtuse to me (he states the issue isn't completely explanable in the context of his argument).
Religion Explained is a fascinating scientific treatise on a unique and undeniably significant form of human behavior. This is a fairly complex work (a behavioral science background is certainly helpful), but only to the extent necessary to form a coherent, comprehensive argument. Boyer has shown undeniably that the etiology of religion is far more multi-faceted than most people infer (both scientists and non-scientists). While his argument will certainly be refined as the various conceptual elements evolve and more research emerges, this new, scientifically vital approach ro religion will likely prove to be a monumental achievement.