Although most people have two kidneys, only one kidney can function just as well as two. You may need to take precautions to avoid injury and see a doctor for regular kidney health tests.

Roronoa Zoro, the second strongest member of Straw Hat Pirates (Image via Eiichiro Oda/Shueisha, One Piece) Aiming to surpass Dracule Mihawk and become the World's Strongest Swordsman ...