When Marius, a young male giraffe at the Copenhagen Zoo, was shot to death by his keepers a few days ago, the world caught its breath. How could the zoo and Marius's keepers do such a thing—particularly when people around the world were clamoring for the zoo to spare him?

Zoos, most of us think, are meant as safe havens for animals, places where they are loved and protected. Zoos tell us that they are educational places, too, where we can watch and learn about creatures we might otherwise never have a chance to see.

Zoos also bill themselves as the only places where certain highly endangered species, such as the Hawaiian crow, survive.

Indeed, zoos say this is why we