Mother Nature Network: The Aldabra banded snail was believed to have been driven to extinction by climate change, but researchers have found a few stragglers precariously hanging on to existence. Climate change, widespread pollution and human development have caused what scientists are calling the 6th great mass extinction in Earth's history. It's a grim projection, but occasionally a species offers a small glimmer of hope against the odds. Take, for instance, the "extinct" Aldabra banded snail, a small air-breathing...