The Pak are a fun concept but they are hardly an explanation for human evolution. In those books he is saying that the symptoms of old age, loss of hair, arthritis, loss of teeth etc are actually poorly formed steps in the transformation to the Protector phase. Of course this ignores that we see similar symptoms of age in most animals and in pretty much all mammals.

Your point is well taken about Ringworld though.

Larry Niven is by far my favorite creator of Aliens. The Jotok are the closest example to the type of alien Paul Burke is talking about and the backstory of Ringworld parallels what Carol was just talking about.