Humans are so closely related to great apes that some scientists believe we should give them full legal rights and seek their consent before subjecting them to research. Ayala Ochert reports Panchee is a bonobo (pygmy chimpanzee) who speaks English with the aid of a voice synthesiser; Alice is a chimpanzee who communicates through sign language. Somerset Biomedical, a primate laboratory, plans to conduct experiments on them. What follows is a statement from Judge Murray in the case of Panchee and Alice versus Somerset Biomedical, Inc.

"Under the common law, even insane, retarded, senile and very young humans are not automatically precluded from testifying at a trial. But the witness must have sufficient intelligence to perceive, remember and narrate facts to make it worthwhile for the judge to consider their testimony. Do the plaintiffs have sufficient intelligence and ability to perceive, remember and narrate facts to make it worthwhile for me to listen to them? For now, I find that they do."

It would have been a landmark decision, but for the fact that Judge Murray does not exist and Panchee and Alice - though based on real characters - are also fictional. But, says Steven Wise, the Harvard law professor who dreamt up this scenario, one day in the not-too-distant future a judge will make a similar ruling, allowing an animal to give evidence in court.

At present, the major obstacle to animal-rights lawyers such as Wise is the sharp line the law draws between persons and things. "When I began to litigate on behalf of non-human animals 20 years ago, I realised that it was almost impossible to make any sort of headway as long as they were considered property or 'things'," Wise says. In his forthcoming book, Rattling the Cage: Towards Legal Rights for Animals, Wise presents the legal and scientific arguments for redrawing that line to include our closest relatives - chimpanzees and bonobos - in the category of "legal persons".

It would not be the first time the line has been redrawn. Until a few generations ago in the US, black slaves were regarded as "property". But, just as Enlightenment thinking made it increasingly difficult to justify slavery, many scientists today argue that great apes should be granted fundamental rights, including the right to life and to freedom from torture. The Great Ape Project, headed by Princeton bioethics professor Peter Singer, argues that legal boundaries should reflect newly recognised biological boundaries.

Chimpanzee DNA differs from our own by 1.6 per cent; gorilla DNA by 2.3 per cent. But, significantly, chimpanzee and gorilla DNA also differ from one another by 2.3 per cent. That means that chimps are closer to us than they are to gorillas. But until recently both species were grouped together as members of the "great ape" family. Now, all the great apes - chimpanzees, bonobos, gorillas and orang-utans - have been accepted into the hominid family, previously reserved for ourselves and some of our bipedal ancestors.

Some scientists believe there is still a long way to go. The African elephant is less closely related to the Indian elephant than we are to chimpanzees. Humans and chimps are closer even than the red-eyed verio and the white-eyed verio, two bird species ornithologists have a hard time distinguishing. For consistency, they say, anthropologists ought to include chimpanzees and bonobos in the genus Homo. Or, as University of California Los Angeles physiologist Jared Diamond says, we should perhaps think of ourselves as a third species of chimpanzee.

Such arguments have persuaded some governments to pass legislation granting special status to our fellow hominids. Biomedical experiments on great apes are banned in Britain and New Zealand, but fundamental rights remain elusive. Wise hopes to get round this political intransigence by asking a court whether chimps and bonobos should be classified as "persons".

"What is it about humans that entitles us to fundamental rights? It has to do with our capacity for autonomy. That is what judges value," says Wise, who has reviewed all the latest scientific research on great apes. "I wanted to understand what kind of minds chimpanzees and bonobos have. Everyone who has three or four-year-old children knows that in many ways they are autonomous, and judges have no problem granting them fundamental rights. Chimpanzees and bonobos operate at such a high cognitive level that there can be no doubt that they are autonomous too," Wise asserts.

To be autonomous, an individual must be self-conscious or self-aware. Until chimpanzees were observed preening themselves in front of a mirror, it was assumed that only humans possessed self-awareness. Forty years ago, it was also assumed that humans were the only species that made tools. Then Jane Goodall noticed a chimpanzee strip a branch of leaves and go fishing for termites. Since then, research from Goodall and others has steadily knocked our species off one pedestal after another.

Chimpanzees have impressive logical and mathematical abilities - they can count, understand fractions, even add them. Chimpanzees plan ahead and solve problems. Chimps and bonobos are also strongly empathetic, aware not only of their own but also others' minds. Washoe, the world's first "signing" chimp, lost two babies, one through miscarriage and the other shortly after birth. When one of the graduate students at her Central Washington University home became pregnant, she was very interested and often inquired about the "baby". That graduate student also miscarried, but Washoe continued to ask about the baby. When the student explained in sign language that the baby had died, Washoe looked her straight in the eye and signed "cry" on her cheek in sympathy.

When a signing chimp named Bruno met up with an old friend, many years after being sold to a biomedical lab, the first thing he said was: "Key out!" Grammatical or not, such statements tell us a great deal about the autonomy of the individual, says Wise.

Roger Fouts, a psychologist at Central Washington University and the person who taught sign language to Washoe, is a strong advocate of rights for chimps, but he is sceptical that one will ever give evidence in court. "Putting a chimpanzee in a courtroom is, I think, as ridiculous as putting a human in a fish bowl and expecting (him or her) to breathe," he says. "The real justification for granting apes rights should come out of our recognition that they are a 'people' with a great diversity of cultures," he concludes.