Hippos are people too - at least, that is, in the judgment of a US Federal Court, which has for the first time in its history recognised nonhuman animals as legitimate plaintiffs with legal rights.

The "Community of Hippopotamuses Living in the Magdalena River", as they are officially known in court proceedings, are the descendents of four animals that once belonged to the notorious Colombian drug baron Pablo EscobarThe "cocaine king" was the wealthiest criminal of all time, controlling much of Colombia's lucrative drugs trade and amassing a fortune of around bn.. When Escobar was killed in 1993, his collection of exotic animals was dispersed to zoos all over the world. Only the hippos, deemed too dangerous to capture, were allowed to roam free. 

Since then their population has exploded to 120, and it is still growing fast. Although they are much loved by locals, they are also a menacing invasive speciesA non-native species that causes harm to an existing ecosystem by overpowering other species or bringing new diseases, usually after being introduced because of human activity., attacking fishermen and causing havoc in the local ecosystem. This year the government finally decided to wipe them out once and for all.

But the hippos had a saviour: the lawyer Luis Maldonado. He argued that the hippos had a fundamental right to life, and that they should be sterilisedSterilisation is surgery that prevents a human or animal from producing offspring. rather than killed. To aid his case he called on two wildlife experts in Ohio - and that is where the historic judgment came in. The US court accepted the legitimacy of the complaint, the scientists gave their evidence and the sterilisation campaign is already underway.

"In granting the application," said a representative for the Animal Legal Defence Fund, "the court recognised the hippos as legal persons". It is a momentous precedent in American law: humans are no longer only things or possessions, but beings with rights and interests that must be respected.

Animal rights campaigners, as well as some scientists and philosophers, have long argued that personhoodThe legal concept of personhood is not limited to humans. In the USA, for instance, corporations are treated by law as "persons" that have interests and rights. In some legislatures, such as India and New Zealand, legal personhood has been granted to rivers. should not be limited to our species alone.

Chimpanzees have proven to possess many qualities that were once thought of as human. They can remember the past and imagine the future. They show self-consciousness and awareness of other minds. In interactions with humans they respect moral principles. They can communicate information and pass on skills. One chimp even adopted a kitten as a pet. It is not so easy to think of a quality that clearly sets humans apart.

Categorising certain animals as "people" would mean that their interests must be respected by law. Crucially, they would have the right of habeas corpusHabeas corpus petitions are usually used for people detained in jails or mental health hospitals. It is Latin for "produce the body". : it would be illegal to hold them captive against their will.

This does not mean that all animals would have rights identical to those of humans, or even to each other. "Nobody," says the philosopher Glenn Cohen, "is saying that goldfish should be allowed to vote." But to discriminate on biology is "speciesistThe term "speciesism" was popularised by the utilitarian philosopher and animal rights activist Peter Singer: discrimination on the basis of differences between species when those differences are not morally relevant (such as eating pigs but not cats).", he says. 

If it's wrong to deny someone personhood because of their race, say animal rights activists, it's wrong to do so because of their species. Why should it matter whether an animal has claws or fingers as long as it can feel pleasure and pain, sorrow and love? End speciesism, they urge, and the cruelty that it allows.

Nonsense, counter others. Chimps and dolphins may be smart, but only we have complex languages, cultures, morality and law. Human life and freedom is incalculably more precious than that of any other species, they say; those who question that diminish the sanctity of human rights.