CNN ran an article asking what the world's greatest achievement is. People posted the computer, fire, internet, printing, getting to the moon, the airplane, music, and more.

I'd have to go with language, and representative government (a.k.a. by the people, for the people, of the people) as the close second, and evolutionary theory as third. The second is in a sense more genuine, because theorists are arguing more and more convincingly that language structures are in fact innate.

Language emancipated us from the rest of the animal kingdom; It changed everything, as it allowed for communication, trade, barter, and of course the recording of history. Representative government emancipated us from Hobbes' state of nature, and it is the single greatest leap of selflessness and co-operation in the history of a terribly violent species; included in this leap is the abolishment of slavery, a worldwide practice until very recently in our hsitory. Evolutionary theory emancipated us from religious and supernatural explanations for the complexity of the biological world.