Dance is the best way to physically express music and the worst way to express a coherent thesis. Here's a guide to the history behind popular dance styles and what they're up to today:

• Jazz: Origin: Jazz dance was invented to go along with jazz music, which was invented to go along with whiskey and sinful thoughts about close talking with a stranger.
Today: It's still one of the most sultry types of dance around, inducing wails of desire from bugles and trumpets everywhere.

• Hip-Hop: Origin: Short for hippocampus hopscotch, hip-hop is a cerebral form of dance that involves absorbing beats, thinking about them, and regurgitating them into body movements a few hours later.
Today: Hip-hop is popular in movies with confrontational names, in music videos, and in nightclubs that are just live versions of music videos.

• Ballet: Origin: Ballet originated in France as a way to train people to be more graceful so that they could more easily slide out of guillotines.
Today: Now it's just a really nice dance.

• Tap: Origin: When a group of schoolchildren tromped home one day through puddles of molten metal and ruined their perfectly good buckled shoes, they discovered a new type of dance used to confound adults.
Today: Tap dancers stomp louder than the notes of a song so that listeners won't be hypnotized by lyrical propaganda or brain-infecting melodies.