Oliver Kamm in The Times:
It’s a tantalising notion that the faculty of language may be attainable by other species. However, the case of Koko does not demonstrate this. Our report, by Ben Hoyle, scrupulously injected this note of caution: “Some experts questioned the extent to which people projected human feelings on to messages from Koko and the handful of other primates who learnt sign language . . . Others insisted that the animals had broken down barriers between their world and ours.”
The sceptics are right. The people making extravagant claims about Koko are typically not linguists. This matters not just because they lack expertise but because they misunderstand the communication that the primates are supposedly using. The cognitive scientist Steven Pinker pointed this out in his great book The Language Instinct (1994). American Sign Language (ASL), like any other sign language, isn’t a system of gestures and pointing. It’s a complete system of grammar with a full range of meanings. The gestures by Koko and other primates were just that: signals that the researchers read messages into.