Bonobos - or "pygmy chimpanzees" - can, in effect, talk, with a little help from a computerised synthesiser, or so at least say Sue Savage-Rumbaugh and her husband, Duane Rumbaugh, of Georgia State University, Atlanta; but although this claim is intriguing, it is not as exciting as the newspapers have been making out, and the discussion on animal rights that has inevitably ensued has been merely irritating. In a nutshell: there is as yet no good evidence that the bonobos' apparent linguistic skill is qualitatively the same as ours; and the matter of their rights is not affected, whether they can speak or not.
Chimpanzees cannot talk, not least because their larynx - as in all other mammals except us - is high in the throat and serves as a valve to stop water running down their windpipes as they drink. Only humans have a larynx slung low, where it can resonate (the voice box), to produce something more than a grunt or a miaow. So those who have investigated the putative linguistic skills of chimps, beginning with Robert Yerkes in the United States in the 1920s, have typically tried to teach them American sign language.
The results have often been impressive. In particular, in the late 1970s, Allen and Beatrix Gardner claimed that their protege Washoe knew more than 100 signs and could string them together into simple sentences. Here, surely, was primordial language skill. Yet Herbert Terrace, of Columbia University, New York, an erstwhile supporter of the Gardners, now says that Washoe and her fellow linguists merely picked up cues from their investigators, like clever Hans, the famous counting horse.
But there is a more fundamental issue, first articulated properly by Noam Chomsky, at the Massachusetts Institute of Technology, in the 1960s. B F Skinner, who carried the behaviourist flag through the middle decades of this century, argued that people learn language in much the same way that circus elephants learn to pirouette: they associate particular sounds with particular circumstances and are rewarded when they get the connection right. Language, in short, is simply a special application of general mental ability.
But this "model", said Chomsky, does not fit the facts. Children learn their own languages within a few years - Cantonese, Geordie or Morningside, it makes no difference - at a time when their general cognitive skills are primitive; they cannot learn arithmetic, for example, at that stage of life. They learn the local language, furthermore, with minimal cues: from almost random sentences coming from all angles, they infer the extraordinarily subtle underlying rules - imperatives, subjunctives, the whole shooting match.
Although these rules are not made explicit until secondary school, when children already speak perfectly, by the time children do learn to think clearly, they also lose the ability to pick up new languages. So language, said Chomsky, cannot simply be a subset of general learning. Children must be born with a customised "language module" in their brains in which rules of grammar are already embedded and into which vocabulary is slotted. Further, all the many thousands of human languages in the end prove to have a similar "deep structure" - subject, object, verb, conditional clauses; this grammar is universal.
Many, since, have offered elaborations. Terence Deacon, in his admirable The Symbolic Species, suggested that languages and brains have co-evolved, with the languages self-selected for user-friendliness. Chomsky himself refuses to acknowledge that his putative language module could have evolved at all by Darwinian means, though many feel that this position is downright perverse. All in all, though, Chomsky's view holds the day: language skill, whatever it is, seems to be special. It must have evolved (pace Chomsky) by borrowing pre-existing, more primitive skills. But human beings don't and can't learn language simply by applying a general ability to think to the particularities of words.
Many animals produce sounds of their own that symbolise aspects of the world at large and are effectively "words". They may learn human words, too. The mahouts of Asia expect their elephants to learn scores of commands in the course of their working lives. The Rumbaughs' star bonobo, Panbanisha, apparently knows thousands of words. Clever animals, such as bonobos, can join words together, apparently expressing novel thoughts. But virtually everything that animals do in the way of language can be explained in behaviourist terms. They learn to associate sounds or signs with objects and actions, just as a dog associates the rattle of the lead with walkies; and some, such as the Gardners' chimp Washoe, will shuffle combinations of signs until they receive the required reward, as in "drink, fruit, want" - which looks like a sentence of a kind.
Animals seem, in short, to be doing precisely the thing that Chomsky said humans do not do: applying general cognitive skills to collections of words. The putative language module, with syntax already built in and allowing infinite flexibility, is lacking - one of the few human skills that really does seem to be exclusively human. Animals cannot speak like us; it's just that the clever ones can use other skills to produce a plausible imitation.
Such ingenuity is impressive, however, even if it is not true language; and this raises another issue. Rene Descartes proposed in the 17th century that thinking depends on words, and since animals don't verbalise, they can't think. Philosophers, scientists and slaughtermen went on believing him for the next 300 years, vindicating appalling cruelties by impeccable Gallic logic.
Science needs measurement, and since we cannot measure the thoughts of animals - if they have any - we must be content to measure their behaviour. So the behaviourists set out to explain what animals do, treating them as if they were simply automata with not a thought in their heads.
Not till the 1980s was it finally proved beyond doubt that although a clockwork toy may emulate a worm or do a fair imitation of an ant, it could never match a pig or a chimpanzee. Such creatures really do work things out and make decisions, guided by their emotions, just as David Hume suggested we do. The much-despised anthropomorphism could thus give deeper insight than the apparent rigours of behaviourism. The task, as Terrace said, circa 1984, "is to explain how animals think without human language".
Today serious biologists have growing respect for the thoughts and emotional depths of animals. At the very least, the Atlantan bonobos must reinforce this respect. To some, too, including me, it has long been self-evident that we should afford "rights" to animals. Each individual agrees to take seriously the things that are important to other individuals, and "rights" is a shorthand way of expressing this general principle.
Some moral philosophers suggest that there can be no rights without responsibilities; but such conditional clauses are purely arbitrary - written in to enable philosophers to put their cats out at night with a clear conscience. We should be prepared to afford "rights" to others without any quid pro quo. We should be good to chimpanzees not because they might resemble us but simply because they are chimpanzees and, as such, like dogs or pigs or anything else that breathes and is aware, should be deemed worthy of respect.
Colin Tudge is a research fellow at the Centre for Philosophy at the London School of Economics