Sartore is a National Geographic Explorer, wildlife photographer, and conservationist. In 2006, Sartore founded the Photo Ark project to show the world the beauty of biodiversity and inspire ...

To honor Koko's memory, National Geographic is republishing "Conversations With a Gorilla," our October 1978 cover story written by Francine Patterson, the psychologist who taught Koko how to sign.

“We don't know how long they live or how fast they grow in the wild,” says Tierney Thys, a marine biologist with the California Academy of Sciences and a National Geographic Explorer.