In another life (college) I was a behavioral ecologist. I studied Koko. This is my favorite Koko story.
Koko was not the only gorilla in her study group, just the first (and apparently, the smartest). She had a number of compatriots over the years including a younger male named Mike. Mike was not quite as good as Koko at signing. Sometimes he'd forget signs that he already knew in the heat of the moment For example, in order to get them to learn and use the signs they would require the gorilla to, for example, ask to go to one another's cages in order to play. Mike would ask to play but would blank on simple things the researchers knew that he knew. Koko tended to get impatient in these situations, and would run back and forth along the fence separating their enclosures, frantically signing things like "Think, Mike" and "Hurry". Well, one day, when Mike had blanked on, of all things, Koko's name, Koko started getting really frustrated. Finally, she stopped running around, sat down right in front of Mike, and signed "Koko is a good girl." At which point, of course, Mike was able to remember the sign for his friend.
Also, if you ever want proof that humans aren't alone in the development of higher intelligence, take a moment to learn about Kanzi the bonobo.
