By Tom Geoghegan
Apes and humans have common ancestors but should they have the same rights? An international movement to give them "personhood" is gathering pace.
What would Aristotle make of it? More than 2,000 years after the Greek philosopher declared Mother Nature had made all animals for the sake of man, there are moves to put the relationship on a more equal footing.
Judges in Austria are considering whether a British woman, Paula Stibbe, should become legal guardian of a chimpanzee called Hiasl which was abducted from its family tribe in West Africa 25 years ago.
The animal sanctuary where he has lived is about to close and to stop him being sold to a zoo, Ms Stibbe hopes that she can persuade the court he deserves the same protection as a child.
APES AND US
Gorillas, bonobos, orang-utans and chimps are great apes
Chimpanzees and bonobos differ from humans by only 1% of DNA and could accept a blood transfusion or a kidney
All great apes recognise themselves in a mirror
Elephants and dolphins show similar self-awareness
Great apes can learn and use human languages through signs or symbols but lack the vocal anatomy to master speech
Great apes have displayed love, fear, anxiety and jealousy
In 1997 the UK government banned experiments on great apes but not on primates such as marmosets and macaques
Sources: Ian Redmond, Charlotte Uhlenbroek
Spanish MPs are also being urged to back a similar principle, one already endorsed by the Balearic parliament and held dear by the international organisation The Great Ape Project - that apes be granted the right to life, freedom and protection from torture.
So should apes such as those at London Zoo, which opens its Gorilla Kingdom on Thursday complete with gym and climbing wall, get the same rights as their zookeepers?
They need greater protection in the eyes of the law, says Ian Redmond of the UN's Great Apes Survival Project, who believes welfare groups could use guardianship as a way to rescue ill-treated apes.
Some rights are conferred on apes but only because they are endangered. And the international trade ban is flouted in Africa and South-East Asia, where mothers are shot and their infants shipped off as pets, circus performers or lab animals. Vivisection on apes is banned in much of Europe but still goes on in the US and Japan.
"Apes are special because they are so closely related to us," says Mr Redmond. "Chimpanzees and bonobos are our joint closest living relatives, differing by only one per cent of DNA - so close we could accept a blood transfusion or a kidney. Gorillas are next, then orang-utans."
But there is a stronger cognitive argument, he says, because the apes' intelligence and ability to reason demands our respect.
"Show a gibbon a mirror and the reaction suggests he or she thinks the reflection is another gibbon. But all the great apes have passed the 'mirror self-recognition' test and soon begin checking their teeth or examining parts of their body they couldn't see without the mirror. This self-awareness surely suggests that they know they exist."
Apes also share a range of human emotions, says zoologist Charlotte Uhlenbroek, who thinks they should be afforded legal protection enshrined in law.
They have a similar lifespan to humans and form strong family bonds which they maintain for life, she says. And apes have displayed a tenderness which could be described as love, anxiety when separated, and fear, jealousy and trauma.
"If I was an alien from Mars and looked at human society and a society of apes then in terms of the emotional life I would see no distinct difference, although we live very different lives because of language and technology."
Giving them rights does not mean throwing open all the cage doors because some zoos are important to preserve the species, but it is vital to establish a principle that apes should not be treated like objects, she says.
Daniel Sokol, a medical ethicist, says apes possess cognitive and emotional faculties that make them worthy of moral consideration.
"Justice and consistent thinking require that we treat non-human animals who share morally-relevant properties in a respectful way, and that surely means giving them the opportunity to flourish and not be tortured or subject to cruel or degrading treatment."
But Steve Jones, professor of genetics at University of London, says human rights are a construct which can't be imposed on animals.
"Where do you stop? It seems to be that being human is unique and nothing to do with biology. Say that apes share 98% of human DNA and therefore should have 98% of human rights. Well mice share 90% of human DNA. Should they get 90% of human rights? And plants have more DNA than humans."
Chimps can't speak but parrots can. Defining creatures and allowing them rights based on criteria invented by one group is itself an enormous breach of human rights, he says, and one need look no further than Austria in 1939 to see why.
"Rights and responsibilities go together and I've yet to see a chimp imprisoned for stealing a banana because they don't have a moral sense of what's right and wrong. To give them rights is to give them something without asking for anything in return."
There is a moral case to make about animal welfare, he says, but it has nothing to do with science.