Sundiver

(Admittedly a series, not one book.) These represented a memorable introduction for me to the notion of patron species “uplifting” (genetically engineering) client species to improved sentience. A key example is the uplifting of dolphins by humans. We are introduced to many variants of dolphin evolutionary efforts, and the struggles involved in uplifting. There are also many examples of aliens uplifting other aliens, so you won’t be disappointed by the variety offered by David Brin. Added to that, I contacted him after publishing my first book, and he was gracious and encouraging in his reply, so I’m biased.