Joseph Stromberg in Smithsonian Magazine: To the best of our knowledge, the mechanical gear—evenly-sized teeth cut into two different rotating surfaces to lock them together as they turn—was invented sometime around 300 B.C.E. by Greek mechanics who lived in Alexandria….
via 3quarksdaily http://www.3quarksdaily.com/3quarksdaily/2013/09/this-insect-has-the-only-mechanical-gears-ever-found-in-nature.html