Representatives for two chimpanzees argued before a New York judge on Wednesday, in the first hearing of its kind over their “personhood” rights and freedom from a research institution.

Steven Wise, the lead attorney for the Nonhuman Rights Project, the group arguing on behalf of the chimps, said that the apes are unlawfully imprisoned and that the court should relieve them. They are “autonomous and self-determining beings”, he argued, and therefore deserve the right to bodily liberty.

He cited some of the same evidence that in April convinced judge Barbara Jaffe to grant the historic hearing, and spoke about research on chimpanzee intelligence, emotions and consciousness. He argued that chimps should not be classified as legal “things” if they share more in common with humans than not.

The chimps, named Leo and Hercules, are kept at Stony Brook University, where researchers use them in locomotion studies. As part of New York’s state university system, Stony Brook is represented by the state attorney general’s office.

Assistant attorney general Christopher Coulston argued that the case could set a bad precedent on animal rights, opening the possibility of court cases on the rights of zoo animals or even pets.

In a brief, he described the petition as a “radical attempt” to extend rights that “could set a precedent for the release of other animals”, such as those “housed at a zoo, in an educational institution, on a farm, or owned as a domesticated pet, and enmesh New York courts in continuing litigation”.

Coulston and Wise sparred through much of the hearing on how to interpret the centuries-old legal principles of unlawful detainment, such as the question of legal standing.

In December, a state appeals court ruled against a petition from the group, deciding that a 26-year-old chimpanzee named Tommy cannot be a legal person. In the court’s decision, justice Karen Peters wrote that chimpanzees deserve protections and share qualities with people, but do not participate in society and cannot face legal consequences for their actions.

The Nonhuman Rights Project counters this argument by noting that some humans, such as children and disabled people, receive full rights and have unquestioned “personhood”.

New York judge asked to rule on whether chimps are ‘persons’. Link to video

In January, another appeals court decided against the group, this time rejecting a petition on behalf of a chimpanzee named Kiko. That court ruled that it could not grant a habeas corpus petition because the group is trying “only to change the conditions of confinement rather than the confinement itself”.

The Nonhuman Rights Project has sought to take the chimpanzees from their owners in New York to a sanctuary in Florida named Save the Chimps. Wise argues that that sanctuary, home to more than 250 chimpanzees on a series of islands, is as close to a natural environment as the animals can have in the US. The group is appealing its failed petitions.

Last week a Gallup poll found that almost a third of Americans support the idea of animals having the same rights and protections as humans, but the poll did not enter specifics of rights or species.

Attorneys, law professors and researchers disagree about personhood for chimpanzees and the ramifications of such a decision. Some, such as Richard Cupp of Pepperdine University and Richard Epstein of New York University, argue that chimpanzees may deserve greater protections but not human rights, and that arguments comparing the primates to children distort the issue and raise intractable, and impractical, questions for the courts.

Others, including David Favre of the University of Michigan and Cass Sunstein of Harvard, have argued for limited rights for some animals. In his book on animal rights, for instance, Sunstein suggests: “We could even grant animals a right to bring suit without insisting that animals are persons, or that they are not property.”

Researchers submitted briefs on behalf of both Stony Brook and NhRP for the case. A group of philosophers called Center for the Study of Great Ideas took up the argument that chimpanzees cannot bear responsibilities for the university, for instance, while primatologist Christoph Boesch and behavioral psychologist James Anderson have submitted on Wise’s side.

The chimpanzees did not appear in court.

Jaffe will rule on the case in the next one to two months, and has been careful not to tip her hand. Jaffe struck out the words “habeas corpus” from her April order to avoid the suggestion that she implicitly recognized the legal personhood of the chimpanzees. But Jaffe also did not dismiss the case on technical grounds, as the state attorney general’s office had requested, instead pressing on to confront “the condition of personhood”.