Probably related to wild animal biology, the requirements, and so on. But that was, that came much earlier. That came recently, rather recently. Earlier, the focus was how the exhibit looked like, with material available. You know that gunnite, the fake rock, or artificial rock once conquered the American zoos. Not all animals are cave dwellers, but from elephant to chimpanzees, they were made into cave animals. That changed a little bit. Easier way out, it was.
