Maybe what it's really meant to communicate is the question "How different are we from the apes?"
It's a pretty classic archetype, the hero who returns home, and finds it's no longer really home, that it is all that he despised abroad, and it's essentially the experience that a satirist is trying to give his/her audience: you've read my recasting of things, now how far, really, is your "reality" from it? And the original book was, I am told, a satire of sorts (not in the funny sense). Similar idea to the soldier who returns home victorious, only to be feared for his/her murderousness (seen, iirc, in this movie, when one of the humans shies away from an ape who just defended him); Similar, I think, to some of the sentiments in Gulliver's Travels (Swift- satirist again!); Similar to the real experiences, perhaps, of ocuntless people, eg (more crudely) Lawrence of Arabia.
Similar, even, for that matter, to the end of the Lord of the Rings (tho' I've never read it)