To this list of my favorite books by Lewis-Williams I can now add Conceiving God: The Cognitive Origin and Evolution of Religion (2010). In it Lewis-Williams' returns to the cave and the neurology of the Homo Sapiens who left signs of their emerging religious sensibilities on its walls. The core of his argument, literally and conceptually, are found in chapters five through nine, where he applies his deep knowledge of archeology and anthropology to questions surrounding the origin of the religion impulse and all its subsequent accretions. Lewis-Williams makes a compelling case that we modern humans are prone to religious experience - the numinous or the mystical - due to our neurology and biochemistry. Once we had religious experiences our efforts to contextualize them resulted in religious belief - orthodoxy. Religious belief among members of small social groups resulted in religious behavior - orthopraxy. While Lewis-Williams accepts religious experience as all but inevitable, he is no fan of traditional religious organizations and their tendencies toward political intrigue, coercion, and violence.
In some ways Conceiving God is his most personal book to date. There is an edge to his early and closing chapters that theists (and some accommodationists) may find off-putting , but Lewis-Williams is not nearly so abrasive as some of the new atheists and he's a better writer. On balance I found his work bracing and a welcome return to the cave where our humanity took form.