René Descartes was robust on the matter of animals: essentially auto­mata, they do not have language so they do not think. In our own time, Noam Chomsky has insisted that language is a uniquely human attribute. None of this has stopped people, many of them showmen and charlatans, from trying to teach animals to speak.

Until quite recently experiments to teach animals human language, and through that to explore their cognitive abilities and their similarities to us, were both academically respectable and fascinating to the wider public. One of the last of those experiments was Project Koko, and it continues to this day. Koko: The Gorilla Who Talks to People (15 June) told the story.

In 1972, Penny Patterson, a psychology student at Stanford University in California, was given a baby gorilla by San Francisco Zoo, on which to base her PhD thesis. Of course, she did not attempt to teach Koko to speak: ape physiology makes that impossible. Instead she taught her American Sign Language.