According to a New York judge, two chimpanzees now have a right that until Monday was reserved for humans. The chimps, used in research at Stony Brook University, may never actually be released, but the court’s move represents a historic change in thinking about animal rights.

Here’s what happened: In December 2013, the Nonhuman Rights Project filed lawsuits in the New York Supreme Court on behalf of four privately owned chimpanzees, considered property in the eyes of the law. The lawsuits sought to have the chimps moved to Save the Chimps, a Florida sanctuary and, more importantly, asked that they be declared legal persons, not with full human rights but with a basic one: not to be owned and caged.

Since then, courts have heard the cases several times. Preliminary arguments have focused on whether a court could issue writs of habeas corpus calling upon the chimpanzees’ owners to justify their captivity. If they can’t justify it, the prisoners have to be released—a process set in motion Monday by Justice Barbara Jaffe. She issued the writs on behalf of Hercules and Leo, the Stony Brook chimps. It’s the first time habeas corpus, historically used to free slaves and people wrongly imprisoned, has ever been extended to a species other than Homo sapiens.

"It's a breakthrough. The judge is implicitly saying that chimps are—or at least could be—persons," says Steven Wise, an attorney and founder of the Nonhuman Rights Project.

Things haven’t gone as well for the chimps in the two other cases. In the case of Kiko, a chimp owned by a couple in Niagara Falls, appeals court judges in January told the Nonhuman Rights Project that habeas corpus didn't apply because the Save the Chimps sanctuary is merely another kind of captivity. In the case of Tommy, a 26-year-old chimp kept in a warehouse in Gloversville, the appeals court concluded in December that rights are given only to individuals capable of fulfilling social obligations and responsibilities.

The decisions hint at the deep unease with which many people—not least judges reluctant to rock the legal boat—view the idea of legal rights for a nonhuman. Legal scholar Richard Cupp has argued that expanding personhood to include chimpanzees would cheapen human personhood. Others have worried that, if given to a chimpanzee, rights might be inconveniently extended to other animals, such as chickens or lab mice.

Chimps, though, may deserve a special status. In affidavits in the Nonhuman Rights Project lawsuits, nine primatologists argued that chimpanzees are thoughtful, independent beings to whom freedom is likely as meaningful as it is to us. "Wow. Wow. Wow. This is incredible," said Mary Lee Jensvold, a primatologist and former director of the Chimpanzee and Human Communication Institute, upon learning of Hercules and Leo's habeas corpus. Jensvold filed one of the affidavits. "I didn't think this would happen so soon. It takes so long for attitudes to change. It's a great piece of news, just to know that a judge wants to hear the case."

Hercules and Leo's case was originally dismissed on a technicality, but the Nonhuman Rights Project refiled it last month. Now that the writ of habeas corpus has been issued, Stony Brook University—represented by the attorney general of New York—must appear in court May 6 and justify Hercules and Leo's captivity. If the Nonhuman Rights Project wins, Hercules and Leo will go to Save the Chimps, and the door will open to further legal challenges to the captivity of chimpanzees—and perhaps other animals—in New York and other states with similar laws.

Jo-Anne McArthur

"It's a big step forward," said Jonathan Lovvorn, senior litigator at the Humane Society of the United States. "Getting your day in court is always a victory." Lovvorn cautioned that the habeas corpus may simply have been a procedural formality: perhaps Justice Jaffe granted them without truly believing that chimps can have rights. Yet it could also be argued, said Lovvorn, that simply issuing the writs—regardless of whatever decision ultimately is made—implicitly recognizes chimp personhood, since under New York law habeas corpus can only be given to a person. Even if the judge decides against Hercules and Leo, the precedent is set that a chimp is person enough to deserve a hearing.

At Stony Brook University, Hercules and Leo are used in studies of chimpanzee movement designed to investigate the evolution of human bipedalism. Little else is publicly known about their lives. Though presently kept at the university, they are reportedly owned by the New Iberia Research Center, a primate facility that has faced allegations of mistreating chimpanzees and illegally breeding them. While strict welfare guidelines regulate the treatment of federally-owned chimps, privately-owned chimps—such as those represented by the Nonhuman Rights Project—are governed by the whims of their owners. Chimp advocates say this patchwork of regulations underscores the need for legal rights.

While a victory would not give Hercules and Leo total freedom, life at Save the Chimps would be an improvement, says Jensvold. Chimps at the sanctuary live outdoors, in family groups—in keeping with chimpanzees' social nature, say supporters of their transfer. But the people at the Nonhuman Rights Project see this victory in more philosophical terms. "They would no longer be confined against their will," says Wise. "We'd be respecting their autonomy, their freedom, and allowing them to live their lives as chimpanzees who are as free as they can possibly be in North America."