The social, economic, and medical problems of a society may lead to the adoption of contradictory food prohibitions. The original purpose of a food prohibition is often forgotten a few generations after the prohibition is introduced. The origin of a food prohibition must be explained with reference to the understanding that the people who adopted and enforced the prohibition had. The social importance of the origin of a food prohibition is independent of the nutritional value of the food prohibited.
Recent medical and anthropological data show that prohibitions on the use of certain foods served important social, economic, and medical functions in ancient cultures. But these data cannot explain the origin of the prohibitions involved, since those who originally adopted and enforced them did not have access to the same data as modern researchers.
Which one of the following is an assumption required by the argument?