Strangely enough I was reading Steven Pinker's "The Language Instinct" a couple of days ago and happened upon his comments about Koko, some of which are reproduced in this review: > > http://filmfanatic.org/reviews/?p=2107 > > Quote: First, looking for a "missing language link" between gorillas and humans is a meaningless endeavor, since homo sapiens took off on a separate branch of the primatology tree long ago; as Steven Pinker points out in his book The Language Instinct, "evolution did not make a ladder; it made a bush." Second, Pinker further notes (and many others have agreed with him) that "people who spend a lot of time with animals are prone to developing indulgent attitudes about their powers of communication", a fact which it's difficult to miss when watching this film. - While I'm familiar with anthropomorphic attachment--that doesn't automatically destroy the evidence nor its implications. How could it? It's possible that the gorillas (and I've seen elephants too) simply mimic behavior for reward, but I think you could construct a test to select against that.