Give someone a leg up

"if you've read it, you have a leg up."

does anyone know where this phrase came from? the history behind it? thanks!

GIVE SOMEONE A LEG UP - To help a person mount an obstacle; to help a person advance in some way. The original sense was to help a person up into the saddle by cupping one's hands for him/her to place one foot in as a "step." From Brewer's Dictionary of Phrase and Fable revised by Adrian Room (HarperCollinsPublishers, New York, 1999, Sixteenth Edition).