Pascal Boyer's "Religion Explained" (2002), based in part on his anthropological field work, treats belief in God as the result of the brain's tendency towards agency detection. Boyer suggests that, because of evolutionary pressures, humans err on the side of attributing agency where there isn't any. In Boyer's view, belief in supernatural entities spreads and becomes culturally fixed because of their memorability. The concept of "minimally counterintuitive" beings that differ from the ordinary in a small number of ways (such as being invisible, able to fly, or having access to strategic and otherwise secret information) leave a lasting impression that spreads through word-of-mouth.