From Wilstar Greetings:
Unlike most of the other nonfoolish holidays, the history of April Fool’s Day, sometimes called All Fool’s Day, is not totally clear. There really wasn’t a “first April Fool’s Day” that can be pinpointed on the calendar. Some believe it sort of evolved simultaneously in several cultures at the same time, from celebrations involving the first day of spring.
It’s better to keep your mouth shut and be thought a fool than to open it and leave no doubt. –Mark Twain
The closest point in time that can be identified as the beginning of this tradition was in 1582, in France. Prior to that year, the new year was celebrated for eight days, beginning on March 25. The celebration culminated on April 1. With the reform of the calendar under Charles IX, the Gregorian Calendar was introduced, and New Year’s Day was moved to January 1.
[Politicians] never open their mouths without subtracting from the sum of human knowledge. — Thomas Reed
However, communications being what they were in the days when news traveled by foot, many people did not receive the news for several years. Others, the more obstinate crowd, refused to accept the new calendar and continued to celebrate the new year on April 1. These backward folk were labeled as “fools” by the general populace. They were subject to some ridicule, and were often sent on “fools errands” or were made the butt of other practical jokes.
This harassment evolved, over time, into a tradition of prank-playing on the first day of April. The tradition eventually spread to England and Scotland in the eighteenth century. It was later introduced to the American colonies of both the English and French. April Fool’s Day thus developed into an international fun fest, so to speak, with different nationalities specializing in their own brand of humor at the expense of their friends and families.
However big the fool, there is always a bigger fool to admire him. — Nicolas Boileau-Despréaux