Where did the pharse "piggy-back ride" originate from?

Answer 1

It's probably a surprise to most people, but it urns out this expression has nothing at all to do with pigs. The expression we know is a corruption of a sixteenth century expression that took various forms: pickback, a pickback, a pick pack, on pick pack, pick-a-pack.

It is generally thought that "pick" is a variation of our word "pitch", meaning "throw."

The full expression probably meant something like "a pack pitched (onto one's back)," or "(a burden) pitched on one's back."

http://www.randomhouse.com/wotd/index.pperl?date=19960816
http://www.answerbag.com/q_view.php/24122
http://www.etymonline.com/index.php?search=piggyback&searchmode=none

Answer 2

Pick-a-back.