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.

The "Community of Hippopotamuses Living in the Magdalena River", as they are officially known, are the descendents of four animals that once belonged to 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, his collection of exotic animals was dispersed to zoos. Only the hippos, deemed too dangerous to capture, were allowed to roam. 

Since then their population has exploded, and it is still growing. 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.. This year the government finally decided to wipe them out.

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. The US court accepted the legitimacy of the complaint, the scientists gave their evidence and the sterilisation campaign is 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 precedent in American law: humans are no longer only things, but beings with rights 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.

Chimpanzees have proven to possess many qualities once thought of as human. They can remember the past and imagine the future. They show self-consciousness. In interactions with humans they respect morals. They can communicate information. 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 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. 

Yes. If it's wrong to deny someone personhood because of their race, it's wrong to do so because of their species. Why should it matter whether an animal has claws as long as it can feel pleasure and pain? End speciesism, and the cruelty it allows.

No. Chimps and dolphins may be smart, but only we have complex languages, cultures, morality and law. Human life and freedom is more precious than any other species; those who question that diminish the sanctity of human rights.