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I'm trying to find a novel written in American English that I read about twenty years ago. It might have been published about thirty years ago. It has the following details:
The aliens are land based, very long lived and communicate via large numbers of cilia on their tentacle tips. They are Masters at biological sciences and are able to recreate the human race based on the radio messages sent long ago by humans. The message contains genetic information as well as cultural information and recordings.
The human race is a short lived, less capable minority compared to the aliens. Some humans become rebellious to the point of violence as a result.
After that is resolved, some humans embark on a return trip to Earth's solar system in a biologically based (giant tree) ship. Earth has meanwhile evolved a new dominant, technological race that they are in instant conflict with. They also find a devolved remnant of humanity similar to ferrets or rats.
I can provide more details if required, just don't want to give too many spoilers.