While it might not seem like it at first, having duplicate Pokemon can actually help you. Extra Pokemon of the same type can be traded to Professor Willow for candy, which can be used to evolve your Pokemon. To do this, tap a Pokemon that you want to get rid of in the Pokemon screen and hit ‘Transfer’ option at the bottom of the screen. Be wary; make sure you don’t transfer the most powerful version (highest CP) of a given Pokemon type in your rush to get rid of your duplicates.
Originally Posted by: gamespot.com