Chita, a female chimpanzee, peers from within her enclosure at a zoo in Asuncion, Paraguay, May 2, 2014. Jorge Saenz/AP

Almost forty years ago Carl Sagan, the astronomer who led the search for extraterrestrial intelligence, pointed out that there are intelligent nonhumans right here on Earth. Chimpanzees are capable of reasoning and have strong emotions. He then asked: “Why, exactly, all over the civilized world, in virtually every major city, are apes in prison?”

That question has still not been answered, but perhaps the day when it will be answered is coming closer. On April 20 Justice Barbara Jaffe, of the Manhattan Supreme Court, issued an order in respect of two chimpanzees, Hercules and Leo, currently in the custody of Stony Brook University. Because the order was headed “Order to Show Cause and Writ of Habeas Corpus,” some headlines trumpeted that a court had declared chimpanzees to be legal persons. But the court had made no such decision, and Justice Jaffe subsequently amended the order by striking out the words “and Writ of Habeas Corpus.”

WIRED Opinion About Peter Singer is Professor of Bioethics at Princeton University and Laureate Professor at the University of Melbourne. His books include Animal Liberation, Practical Ethics, The Life You Can Save, and, most recently, The Most Good You Can Do.

What the order does is require the university to show cause for holding the chimpanzees. That in itself is significant, because it means that the court did not simply accept without argument that the chimpanzees are items of property. The case was brought by the Nonhuman Rights Project, which argues that chimpanzees are legal persons with a right to bodily liberty—which, since the chimpanzees clearly cannot be turned loose, and do not have the skills to fend for themselves in the remaining African forests where chimpanzees still live freely—would mean the transfer of the chimpanzees from the university to a sanctuary where they would have plenty of space and could become part of a social group. The court’s order means no more—but also no less—than that this argument will have its day in court.

Where should we draw the line between those who have basic rights, and those who do not? In 1993 Paola Cavalieri and I founded The Great Ape Project, an organization intended to gain, for our fellow Great Apes, the rights to life, liberty and protection from torture. In The Great Ape Project, a volume of essays that marked the launch of the organization, we were joined by such experts on great apes as Jane Goodall, Roger and Deborah Fouts, Lyn White Miles and Francine Patterson. The evolutionary scientist Richard Dawkins, writers like Douglas Adams and Jared Diamond, and many prominent philosophers and social scientists, also contributed to the volume. All of the contributors signed a declaration pointing out that the mental capacities of the great apes, and their emotional lives, suffice to justify including them within what we called “the community of equals”—that is, the community of those recognized as having basic rights.

The mental capacities of the great apes, and their emotional lives, suffice to justify including them within what we called the community of equals.

This claim is in one sense radical, and in another modest. It is radical because throughout human history, we have only recognized other human beings as part of the community of equals. In the past, of course, we have often not recognized the rights of all humans either, but the human rights movement now enjoys a very high level of acceptance, at least in terms of public statements and declarations, if not always in practice. But the very fact that it is a human rights movement – and that few people even see the need to defend the restriction of rights to human beings – shows that demanding rights for nonhumans goes an important step beyond what is now accepted.

On the other hand the claim made by the Great Ape Project is modest, because rather than seek rights for all animals capable of suffering or enjoying their lives, the claim demands rights only for those who have demonstrated a degree of self-awareness, and a capacity to reason, and whose emotional and social life we can readily see as being on the same level as at least some human beings, including small children. Admittedly, many of those supporting the Great Ape Project, myself included, view it as building a bridge between our own species and our closest relatives that other animals will eventually also cross, but that is a question for another day.

The ethical basis for extending basic rights to chimpanzees and the other nonhuman great apes is simple: chimpanzees are comparable to three-year-old humans in their capacity for self-awareness, for problem-solving, and in the richness and complexity of their emotional lives, so how can we assign rights to all children and not to them? If the claim is that human children have the potential to develop capacities beyond those that chimpanzees will ever have, then we could ask the same question about humans with permanent intellectual disability, of a kind that means they will never surpass chimpanzees in their ability to reason, or their degree of self-awareness. And if, in order to retain the status quo, we say that these humans have greater rights than chimpanzees just because they are members of our species, what are we to say to racists who make similar claims on behalf of members of their race? We can’t just draw a circle around those who are “us” and give them greater rights, because who “we” are is contested. All white males? All white humans? All beings who pass a threshold of self-awareness, or moral agency? All humans? All great apes? All sentient beings?

The hearing at which Stony Brook University will, presumably, argue that Hercules and Leo are its property and have no right to be released has been set for tomorrow, May 27. When Justice Jaffe issues her ruling, we know the full significance of the order she has issued. It may prove to be a false dawn. But one day, surely, we will recognize that there is no good reason to keep apes in prison, nor to deny them basic rights.