This book was very nice, and got a lot more into protectors. I liked the plot of the second one better, but this one was still very nice. There was a huge emphasis on sex again, but I was able to tease out what he was getting at with it. Since all the hominids on the Ringworld practice sex, but in different ways, the species can use it as a bonding exercise without it being a competition for procreation. All other activities will be some kind of competition, but the sex part of it isn’t. This wasn’t clear in the previous two, as there wasn’t as strong a focus on why they shouldn’t mate with their own species. The city builders mention it, but it wasn’t as much a focus.