The big question facing Baltimore’s National Aquarium — whether to keep Atlantic bottlenose dolphins in the amphitheater pool or release them to an ocean-side sanctuary — is the latest twist in the decades-long evolution of American zoos and aquatic attractions from circus-like menageries to portals into the natural environment. […] Alfred Beulig, a biology professor at New College of Florida, said there’s no scientific reason dolphins shouldn’t be held in captivity. But there are reasons why aquariums must take extra care if they do keep them. As mammals, dolphins’ brains work differently than those of other animals, and that requires a different environment than is provided for, say, sharks.