Do zoos do enough for conservation to justify captive breeding?

Knut, the first polar bear cub to survive past infancy at the Berlin Zoo in more than 30 years. His early death caused dismay far beyond the city. Photo: Soeren Stache/dpa-Zentralbild/dpa

Two years ago, everyone in the city of Erfurt was thrilled when rhinoceros Marcita gave birth to a little bull.

The zoo was particularly excited and set up a poll so the public could vote on a name for Marcita's second cub.