Animal rights lawyer Steven M. Wise, as seen in the documentary “Unlocking the Cage,” with a chimp named Teko. (Pennebaker Hegedus Films/HBO)

For several years, an animal rights organization has sought to convince New York courts that chimpanzees kept by private owners are “legal persons” with a right to be free. For several years, the courts have rejected that argument.

New York’s highest court did the same on Tuesday, denying an appeal of a lower court’s refusal to grant writs of habeas corpus to two caged chimps named Tommy and Kiko. But in a striking concurring opinion that was cheered by the chimps’ advocates, one judge wrote that the legal question at the heart of the case — whether all animals are mere property or things — is far from settled.

“Does an intelligent nonhuman animal who thinks and plans and appreciates life as human beings do have the right to the protection of the law against arbitrary cruelties and enforced detentions visited on him or her?” wrote Eugene Fahey, one of five Court of Appeals judges who ruled on the matter. “This is not merely a definitional question, but a deep dilemma of ethics and policy that demands our attention.”

The 5-to-0 vote upheld a June decision by a lower appeals court that, like courts before it, ruled that chimpanzees could not be legal persons because they cannot take on legal duties. The Nonhuman Rights Project, which has asked courts to move Tommy and Kiko to a sanctuary, says the interpretation is flawed. The group’s director, Steven M. Wise, has noted in interviews that both infants or comatose people possess rights despite an inability to assume legal duties and that primate experts say chimps have rights and responsibilities within peer groups and in settings with humans.

But even as he voted with the majority, Fahey appeared to be gripped by the issue — and determined not to let the latest ruling close the door on it. The lower court’s conclusion “that a chimpanzee cannot be considered a ‘person’ and is not entitled to habeas relief is in fact based on nothing more than the premise that a chimpanzee is not a member of the human species,” he wrote in his opinion. “[I]n elevating our species, we should not lower the status of other highly intelligent species.”

Instead of focusing on whether chimpanzees are “persons” or bear legal duties, courts should grapple with whether the animals have a right to be free, Fahey wrote. Expert affidavits, he noted, presented “unrebutted evidence” that chimps have advanced cognitive abilities and communication skills. They share 96 percent of their DNA with humans; are able to plan, make tools and recognize themselves in mirrors; and display compassion and senses of humor, he wrote.

“They are autonomous, intelligent creatures. To solve this dilemma, we have to recognize its complexity and confront it,” Fahey wrote. The issue, he continued, “speaks to our relationship with all the life around us. Ultimately, we will not be able to ignore it. While it may be arguable that a chimpanzee is not a ‘person,’ there is no doubt that it is not merely a thing.”

The Nonhuman Rights Project, which is mounting a similar case on behalf of three elephants owned by a Connecticut traveling zoo, expressed disappointment in a statement that Tommy and Kiko would remain with their owners. But it hailed Fahey’s opinion as “a historic mark of progress in the fight to secure fundamental legal rights for nonhuman animals.”

“We commend Judge Fahey for his willingness to see our nonhuman clients for who they are, not what they are,” the group said. “This opinion should give hope to anyone who knows the time has come for fundamental change in how our legal systems view and treat nonhuman animals.”

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