That's cool to hear that your friend is writing about the topic. It's interesting to explore that aspect of societies through a materialist lens like that. Just off the top of my head I'm thinking right now of how these societies essentially tried to use eunuchs to get around bureaucrats reducing the effect of meritocratic recruitment through generational acquisition of privileges through their offspring. But eunuchs like John the Orphanotrophos still found a way around it.