I'm finally getting around to Nate Silver's The Signal and the Noise - Why So Many Predictions Fail. And this graph from the first few pages is pretty astonishing. One simple breakthrough -- the printing press -- enhanced the spread of ideas by orders of magnitude.
Many scholars see this as a significant moment in the history, not just of civilization, but of social justice. Books allowed people to read about faraway places, and learn about faraway people. It became easier to see through another set of eyes. And once we saw through those eyes, it became impossible to denigrate and diminish the perspective of the other.
Two take home points:
1. Development, whether technological or moral, is not a linear process. It goes through fits and starts, but when it happens, it happens at rates almost unbelievable just a few years prior.
2. Ideas of justice and empathy spread due to perspective shifting. It's not enough for people to see violence -- the pre-literacy era was filled with violence against humans and animals -- they have to interpret it as a violation of some individual. "Some individual not unlike me."
So all you writers out there, get to work!