Koko the gorilla, famous for being one of the first apes to learn sign-language, is also one of the few non-human animals known to keep a pet.
Researchers at The Gorilla Foundation said that Koko asked for a cat for Christmas in 1983. Ron Cohn, a biologist with the foundation, explained to the Los Angeles Times that when she was given a lifelike stuffed animal, Koko was less than satisfied. She did not play with the stuffed animal and continued to sign "sad."
To cheer her up, Koko was given the chance to choose one kitten from a litter as a birthday present in July 1984. Koko selected a gray male Manx from a litter of abandoned kittens and named him "All-Ball".
Penny Patterson, who had custody of Koko and who had organized The Gorilla Foundation, wrote that Koko cared for the kitten as if it were a baby gorilla. Researchers said that she tried to nurse All-Ball and was very gentle and loving.
However, tragedy struck for both Koko and All-Ball. In December of that year, All-Ball escaped from Koko's cage and was hit and killed by a car.
Patterson approached Koko afterwards, who was eager to find and play with All-Ball again. She signed to Koko that All-Ball had been killed.
Koko signed back, "Bad, sad, bad." And then, "Frown, cry, frown, sad."
Patterson also reported later hearing Koko making a sound similar to human weeping. Koko seemed to be mourning for her lost friend.
Although we can never know just how much Koko actually understood the situation, the emotional response seemed clear for all to see.
Just how profound were Koko's emotions? Who can tell... But this makes us wonder, what other species may have sophisticated emotions without us even knowing? It seems humans aren't the only ones who get attached to others, and grieve for their deaths.