For nearly five decades, psychologist Francine Patterson taught a western lowland gorilla named Koko a modified sign language — and Koko reportedly learned more than 1,000 signs, understood 2,000 spoken words, and mourned when her kitten was killed by a c

For most of her life, a western lowland gorilla named Koko was among the best-known non-human animals on the planet. She appeared twice on the cover of National Geographic. She sat with Robin…