The plaintiff in a landmark lawsuit seeking legal rights for a chimpanzee has lost his case—for now.

A New York appeals court this morning rejected the lawsuit, filed by the Nonhuman Rights Project, on behalf of Tommy, a 26-year-old chimp kept alone by his owners in an upstate warehouse.

The Nonhuman Rights Project argued that Tommy should be considered a person—in legal terms, an entity capable of having rights, and in his case one specific right: not to be wrongfully imprisoned.

"Petitioner requests that this Court enlarge the common-law definition of 'person' in order to afford legal rights to an animal," wrote the judges in their decision. "We decline to do so."

Attorney Steven Wise, founder of the Nonhuman Rights Project, said they will appeal the decision to New York's highest court. "We think the court was wrong in some very fundamental ways," he said.

The lawsuit was originally filed last December, along with similar suits on behalf of three other privately-owned chimpanzees in New York. The suits sought so-called writs of habeas corpus; had they been granted, the chimpanzees' owners would have been forced to justify the chimps' captivity.

That would have likely resulted in the chimps' transfer to sanctuaries designed for their care, and would have explicitly acknowledged that chimpanzees, and potentially other animals, can have legal rights. Such a decision would be unprecedented.

Each of the cases was rejected by lower courts, then appealed. Today's decision is the first appeals court ruling.

The judges did not challenge the claim, supported with affidavits filed by nine leading primatologists, that chimps are extraordinary beings: social, emotional and highly intelligent, sharing much in common with their human cousins.

Instead they rejected Wise's argument that legal rights arise from an abiding respect for individual liberty and self-determination. Rather, said the court, rights are contingent upon responsibility. If a chimp can't be expected to fulfill his social duties, neither can he have rights.

"Unlike human beings, chimpanzees cannot bear any legal duties, submit to societal responsibilities or be held legally accountable for their actions," wrote the judges.

"In our view, it is this incapability to bear any legal responsibilities and societal duties that renders it inappropriate to confer upon chimpanzees the legal rights—such as the fundamental right to liberty protected by the writ of habeas corpus—that have been afforded to human beings," they concluded.

The Nonhuman Rights Project had addressed that argument in their brief, countering that young children and adults with severe mental disabilities are not expected to fulfill the social obligations of mature adults, but are still granted legal rights.

While that is true, wrote the judges, "it is undeniable that, collectively, human beings possess the unique ability to bear legal responsibility."

The decision came as no surprise to legal experts and observers. Even those who support the case acknowledge that it's controversial. Still, there was dismay at the court's reasoning.

"It is unfortunate," said primatologist Mary Lee Jensvold, who works with chimpanzees trained to use sign language and filed an affidavit describing their cognitive similarities to humans.

Chimps might not be able to acknowledge our society's expectations, said Jensvold, but it's worth remembering that in their own societies, they are capable—and indeed expected—to perform duties of child-rearing and hunting.

"I'm sure cultural anthropologists could think of many examples of human individuals being transplanted from one culture to another. They don't function very well, and maybe they don't fulfill their rights and duties," said Jensvold. "But we're not going to take their personhood away from them."

David Cassuto, an animal law scholar at Pace University, criticized the Court's rationale that the rights of children or mentally disabled adults is rooted in the collective capacities of humans.

"A habeas corpus petition is about an individual, not a species," said Cassuto. "It has nothing to do with the potential of that individual's species."

There are reasons to be wary of extending legal personhood to chimps—one might feel it's a matter best left to legislatures, rather than courts—but those reasons "are not the ones articulated here," Cassuto said.

To Cassuto, the decision touched on a deeper discomfort with extending a traditionally human concept to a non-human. Indeed, many critics of the Nonhuman Rights Project's arguments say that treating a chimpanzee as a person threatens to diminish the personhood of humans.

"We could see over time some of our most vulnerable humans losing out in a rights struggle if they're in direct competition with some particularly intelligent non-human animals," said Richard Cupp, a Pepperdine University law professor, in an Associated Press interview in October.

Animal law professor David Favre of Michigan University took a longer view of the decision. "I was impressed that the judges clearly understood the full depth of what was being argued, and met it head-on," said Favre. "It really gets to the heart of the issue: Who is a person? Now counterarguments can be crafted."

The idea of rights as being contingent upon responsibilities "is not a principle carved in stone somewhere," said Favre. "I think there's still room for Steve to discuss this and counter that argument. The legal system has a long-standing interest in helping those who can't help themselves."

In a statement issued by the Nonhuman Rights Project, the group said it will soon file an appeal challenging the court's decision.

Wise cited as an important precedent Byrn v. New York City Health & Hospitals Commission Corporations, an abortion rights case in which it was established that personhood, at least in New York state, is not simply a function of meeting social obligations.

"This is not the end of the road," Wise said. "These are the early moments."