Koko, the gorilla who knew sign language, dies at 46

Koko, a 46-year-old gorilla who mastered sign language has died in its sleep at a California preserve on Tuesday, the Gorilla Foundation announced. Koko appeared in several documentaries while a 1978 National Geographic cover featured a selfie the animal took in front of a mirror. "Koko's capacity for language and empathy opened minds and hearts of millions," the foundation said.