Unlocking the Cage, a new documentary on HBO, asks a provocative question: Are animals entitled to the same legal rights as humans?

The documentary, directed by acclaimed filmmakers D.A. Pennebaker and Chris Hegedus, follows Steven Wise, a lawyer and lecturer at Harvard Law School and founder of the Nonhuman Rights Project. After decades working with animal welfare laws, Wise now believes that unless animals, specifically apes, orcas, and elephants, are seen as “persons” by the law (rather than “things”), they will not be protected from inhumane treatment.

“Animal welfare laws have existed since 1821,” Wise recently told the Washington Post. “But they don’t work. One reason they don’t work is they don’t change the ‘thinghood’ status of nonhuman animals. They leave nonhuman animals as things that lack the capacity for rights. All human history shows that the only way that even the most fundamental interests of us human beings is protected is when we become rights-bearers. There’s no reason to think that’s not true for nonhuman animals as well. So long as you’re a thing, you are at the entire mercy of persons.”

Wise has now filed lawsuits on behalf of four chimpanzees held in captivity in New York State, with plans to file a similar suit for an elephant held in captivity.

“It’s kind of terra nova,” he says about his sometimes-experimental legal efforts. “We have to figure out what we can do, but what we know is that where they are now is wrong.”

In the lawsuits, he argues that chimpanzees have the right to habeas corpus, which entitles them to have their case heard by a judge. But legally, habeas corpus only applies to persons, not things. Which is why, according to Wise’s argument, it’s so critical for a court to recognize a chimpanzee as a person rather than a thing.

Wise argues that, thanks to a plethora of recent scientific studies, we know that certain animals, especially apes, are not just things — their minds are capable of complex cognitive functions. Like humans, these animals are self-conscious, have theory of mind, and understand their lives. In fact, these animals are so intelligent that they are aware of what is happening to them and being done to them. In the film, we see the apes communicating with sign language, images on a keyboard, and responding to complex requests from researchers.

“When you imprison a chimpanzee,” Wise says in the film, “he understands that tomorrow he is going to be imprisoned, and as far as he knows it is not going to end.”

In the eyes of the court, “persons” do not necessarily need to be humans. Historically, women, children, and slaves were not legally acknowledged as “persons,” but instead property without any rights. Wise argues, when it comes to animals, we should be on the right side of history.

Around the world, there’s progress in the treatment of animals. In Argentina, a court found an orangutan to be a sentient being. In the United States, the NIH has been phasing out medical testing on chimpanzees. Public backlash has also forced household institutions like Ringling Bros. and Barnum & Bailey Circus to retire their traveling elephants. There has been pushback on the treatment of the orcas at Sea World, following the documentary Blackfish, and officials have vowed to no longer breed the animals in captivity.

So far, courts have yet to side with Wise in the belief that animals should be seen, legally at least, as persons. There is a slippery slope that courts have pointed out — if chimpanzees have rights, can dogs sue too? How about cats?

Wise recognizes this, and right now, he’s focusing his efforts on animals that are incredibly intelligent and humanlike. For Wise, just having the conversation is a step in the right direction.

“All we can do is kick the first door open,” he says.

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