And to think it all started with a naked mole rat.
The year was 2006, and National Geographic photographer Joel Sartore wanted to try making formal portraits of animals in captivity instead of his usual shots of them in the wild. For his first subject, he told a zookeeper, he just needed a creature that might sit still. The naked mole rat qualified.
From that modest beginning came Photo Ark, a joint project of Sartore and National Geographic. Within a 25-year span, Sartore aims to document as many of the species of animals now living in captivity as possible.