It has been a while since I read any of the books but I feel like this is a thing that is explicitly noted in the text of the books here and there. It's certain

It has been a while since I read any of the books but I feel like this is a thing that is explicitly noted in the text of the books here and there. It's certainly in "A Few Notes On The Culture", a post Banks made to rec.arts.sf.written back in 1994: "Humans and independent drones (the Culture's non-android individual AIs of roughly human-equivalent intelligence) are unnecessary for the running of the starships, and have a status somewhere between passengers, pets and parasites." (taken from a copy found at http://www.vavatch.co.uk/books/banks/cultnote.htm http://www.vavatch.co.uk/books/banks/cultnote.htm)