If I write a best seller at age 25, I hope that I can still claim my royalties past age 45. I'd also argue that heirs should also have some period of exclusivity as well. Using the best seller at age 25 example, were I to die an untimely death at age 32 I would again hope that my very young daughter would still be able to receive benefit from my creative works. So author life + 20 years to the first heir (exclusively) would work for me.
In the case of a non-human copyright holder, 50 years seems reasonable can broadly comparable to that of the life of a human creator.
In the case of a non-human copyright holder, 50 years seems reasonable can broadly comparable to that of the life of a human creator.