Dance started out being part of the celebrations when hunter gatherers returned home from a successful trip. It then progressed into part of the courting ceremony to attract the opposite sex, a bit like the birds and the bees. If you've ever seen 'Dirty Dancing' you will see the same basically holds true today.

 The history of Dance is as old as the human race itself. So it is really not possible to say when was it originatd. Researchers have found traces of dance practice from 9000 years old Rock Shelters of Bhimbetka. So it can be said that since time immemorial it has been part of human culture, rituals, celebrations and entertainment etc. You can find details on the link below:
en.wikipedia.org
 

 I think that dance is just a natural part of our self. Even in the very young the need to move in rythym, or repetitive motions is seen. When one is excited they jump, throw their hands in the air or physically express that joy, and i think that this is the essence of dance. It was the previlence of reasons for emotional and physical expression that gave way to what we formally call dance. Once it was an accepted form of expression, the evolution was inevitable.