According to the “Folklore of American Holidays” (REF GT4803.F65 1991), the origin today’s holiday (AKA “All Fools’ Day”) “is uncertain, but it seems to have come about it France as a result of the change to the Gregorian calendar in 1582 when New Year’s was moved from March 25 to January 1. Thus, the first April fools may have been people who failed to make proper adjustment. In Mexico, where the borrowing of trivial items and the failure to return them is a feature, a similar day is celedrated on 28, and some countries like Germany and Norway have two such days on the first and last dates in April.” p 175.