But according to Kagan, who recently traveled to Antarctica to see the penguins there, some animals do thrive at zoos.
"A penguin's life is one of constant attack," Kagan said. "Penguins are brutally attacked by seals, the elements - even their own children are attacking them for food and care. Life is incredibly hard for a penguin in the wild."
In contrast, the penguins at The Detroit Zoo live an "incredible life," Kagan said. "That's not a justification for taking animals out of the wild, of course, and we don't do that." Put simply: "Life is not perfect for animals outside zoos. It's not perfect for animals inside zoos."