Scientists regularly tell us that humans are monkeys and now animal rights campaigners in the United States have gone to court to say monkeys are human.

The Nonhuman Rights Project (NRP) wants the law to agree that chimps are people too as part of a bid to free from captivity a chimpanzee named Tommy.

The simian lives in New York in conditions which NRP describes as a "small, dank cement cage in a cavernous dark shed."

It wants 26-year-old Tommy and three other chimps to be ruled as legal persons, making it illegal to keep them in the conditions.

NRP wants the animals to be protected under a human entitlement not be held for entertainment or research, as a "fundamental right to bodily liberty."

The other chimps which could soon be joining the human race are named Leo, Hercules and Kiko.

NRP president Steven Wise said: "Chimpanzees possess cognitive abilities that are strictly protected when they're found in human beings. There's no reason why they should not be protected when they're found in chimpanzees."

According to Wise, Tommy the chimp looked to be in a "depressed" state after being confined in a trailer park with the other apes as part of an exhibition of exotic animals, in Gloversville.

Wise told Reuters: "He looked terrible. He looked like a caged chimpanzee - they don't move, they don't look at you. They look depressed."

A chimp being classed as a "legal person" might produce some unforeseen consequences, including the possibility of humans and monkeys becoming legally married.

The case continues.