On Koko... Koko's not all she's cracked up to be. Although there is a lot of non-scientific media that talks about her language abilities, there actually aren't very many scientific/peer reviewed articles on her, something that is the source of some contention.

With Koko/many other talking apes the handler does a LOT of interpretation for the sign language, to the point that it starts to feel a bit like reading tea leaves. With Koko, I often feel that the handler goes way too far in this. For example:

    Interviewer: Koko, do you feel love from the humans who have raised you and cared for you? Ely35150 asked that. We'll see what she says!

    Dr. Patterson: She's reading a birthday card.

    Koko: lips, apple give me

    Dr. Patterson: People give her her favorite foods.

    Koko: love, browse drink nipple

    Dr. Patterson: Browse is like... the little foods/snacks we give them.

    Koko: koko loves that nipple drink, go

    Dr. Patterson: She's kissing her alligator.

    Koko: lights off good

At one point Koko signs "nipple", which her handler interprets as "people" since they rhyme. Seeing as how Koko can't speak english, the idea that she understands english rhymes feels like more than a bit of a stretch to me.

Many other scientists have approached the ape speaking thing through a bit more of a skeptical lens, and produced (IMHO) much better work. The work on Nim Chimpsky in particular is interesting - they found that while Nim could associate words with concepts (forming phrases like "give food me eat"), anything resembling syntax, creating new phrases, or a sustained conversation was simply out of his reach.