The Sumerians are the first sign of civilization; early peoples give up the dangerous and uncertain life of the hunter/gatherer for the more permanent life of the farmer/herder. Civilization was arranged in city states; they had a code of laws, currency, and value the good of the community over the family (for example, you could not kill a man for family honor because it would damage the community as a whole).
This is also the first instance of written documents; the Sumerian language was made up of pictographs - pictures that indicated words, the early precursor to the hieroglyph. The most famous document found is the Epic of Gilgamesh, which told the story of the King of Uruk.