From NPR in 2005 --

Reason Behind the Rhyme

Chris Roberts, author of "Heavy Words Lightly Thrown" says, "One of the many versions ran like this. It goes: 'Yankee Doodle, keep it up. Yankee Doodle, dandy. Mind the music and the step and with the girls be handy.' And this particular version was sung by predominantly the British as a reminder to our American friends that dance steps in Europe and in America, the colonies as it was, were different. And it's a reminder to check you doing the steps right and that you're holding the girl in the correct way, which is--so that's one variation of--apparently, there are hundreds and the book could have been devoted entirely to that."

Basically reminding the provincial colonists that it takes more effort than sticking a feather in one's hat to make one fashionable, and it takes study and practice to do fashionable dance steps as well.

Linn