they were not in a natural state, they were conditioned due to 1000+ years of a little voice literally telling them how to be happy, what to do, taking care of them and selectively breeding them.
the zoo was a 100% controlled environment, extremely limited as to any factors that could affect them. there were no seen animals, no weather changes, no change in landscape, limited flora, the space only went so far before hitting the walls and, to them, that was the end of existence. the end. nothing to question past it, that was reality and they happened to be living in it.
and then, again, there was the "little voice" speaking to them every day, taking care of every need, including sex and love.
no religious references? it was the classic garden of eden, ignorance is bliss set-up. they didn't even know the concept of "hurt" or any negative feelings.
you cannot apply the history of humanity's tribalism on earth to the zoo humans, because survival on earth fucking SUCKS in comparison to the zoo. no direction except for the ones people themselves cook up to explain the multitudes of unexplained phenomena (until science gets going), all manner of animals, plants, disease, landscapes, and weather that can and will kill a man, limited resources for an uncontrolled population leading to competition (often violent) and somebody naturally having to lose and lack.the tribal instinct, which itself is the basic cause of civilization proper, is needed to survive on earth
not the zoo.