The Sophists
Societies evolve and change over time. Whether the causes are economic, driven by war, or merely fallout of an evolving political system, the results are the same. New generations have new outlooks and seldom embrace tradition.
So it was in Athens during the middle of the Golden Age, when the Sophists began their rise to prominence. Athens, during that time, had grown more man-centered, not unlike the Renaissance two thousand years later, when traditional views were called into question. The Greeks decided they wanted to rule themselves instead of being ruled by the unseen world of myth.