John Emerson has a long post about the relationship between irrationality and the emergence of new cultural forms. Worth reading. The other day I had a thought: many cultural traits are basically hitch-hiking along. Consider circumcision and the ban against pork consumption for Muslims, in places like Indonesia when tribes convert to Islam they abandon their pigs and circumcision becomes the norm. Why? People have been inventing strange functional rationales for these customs for decades. It seems likely that these practices have a role as ingroup vs. outgroup markers, that is, they’re convenient shibboleths. Food taboos of course impose segregation between different groups if they can’t eat together without transgressing their norms (e.g., Muslims eating at a Chinese house often have issues because of the ubiquity of pork). That being said, an interesting model for the “selection” of shibboleths is that the group in which cultural form or religion x arose tend to serve as a model, and so all sorts of peculiar customs spread outward. For Islam, circumcision and the non-consumption of pork would qualify (circumcision is actually not even a religious sacrament in Islam as it is in Judaism, but simply a custom which has become accepted through consensus as defining a Muslim male). The spread of Roman-Christian culture in Europe had the same effect, Romanitas entailed the spread and adoption of customs and traditions which were not central to the civilizing aspect of literate Mediterranean culture.