April Fool's Day origin

April Fool's Day origin is uncertain. Foolish?
"April Fool's Day, sometimes called All Fools Day, is one of the most lighthearted days of the year. Its origins are uncertain. Some see it as a celebration related to the turn of the seasons, while others believe it stems from the adoption of a new calendar...."
Link: http://www.icontact-archive.com/npqGSbDm0qQigBu6bm9VvkXH3amAM1Am?w=1&sms_ss=facebook&at_xt=4d95f97e222e3f4d%2C0