I ran across this simulation called "A Parable of the Polygons." In a nutshell, it demonstrates how an integrated society can become increasingly segregated over time if individuals harbor even a small amounts of personal bias towards living near their own kind.
It's fun to play around with the numbers. One thing that's interesting is that once segregation occurs, an elimination of bias doesn't result in greater mixing. I'd love to see a version of this with more "shapes" and where the bias can be manipulated to be different for some "shapes" than others.
While this demonstration focuses on physical proximity, it's possible that something similar could happen with regards to the choices people make about the books they want to read (both with regards to the gender or race of the authors or of the characters therein).