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Two adult macaques hold a baby macaque and look into the distance.
Long-tailed macaques in Indonesia.
Gustavo Mejía/Getty Images

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The US uses endangered monkeys to test drugs. This law could free them.

Everything from Ozempic to Covid vaccines is tested on long-tailed macaques. Experts believe many are illegally trafficked from the wild.

Dayton Martindale is a freelance writer and editor covering climate, ecology, animals, and politics, and a PhD student in environmental studies at the University of Colorado Boulder, where he studies the ethics, politics, and policy of human-nonhuman interaction.

Tanya Sanerib has some advice for your next life: “Don’t come back as a crab-eating macaque.”

That’s what Sanerib, international legal director for the Center for Biological Diversity, concluded after looking at data on the vast numbers of crab-eating macaques, monkeys also known as long-tailed or cynomolgus macaques, imported into the United States for animal testing.

These playful, fruit-loving monkeys have the misfortune of being a standard research model used for toxicology testing in the biomedical industry. In recent years, exporters based largely in their native range of Southeast Asia have sold more than 30,000 long-tailed macaques annually to the US, largely for laboratory use.

Biomedical industry demand for long-tailed macaques is so high that, analysts reported last year, a single animal could be sold for as much as $60,000. On arrival at pharmaceutical companies and research institutions, they’re destined to live in cages and face experimentation to test everything from the weight-loss drug Ozempic to Covid-19 vaccines.

US scientists have been using large numbers of these monkeys since the 1970s, when India halted exports of rhesus macaques, and researchers had to find a new, more easily replaceable species for lethal pharmaceutical testing. Long-tailed macaques’ relative abundance in the wild meant they fit the bill.

Unfortunately, they’re not so abundant in the wild anymore.

While the animals proliferate in US laboratories, they are struggling in their native habitat, and the animal testing industry is partly to blame. Long-tailed macaque populations declined by 40 percent from the mid-1980s to 2006, and in 2022, they were listed as endangered by the International Union for the Conservation of Nature (IUCN), a global authority on wildlife threats. The IUCN named several causes for the macaques’ decline, including habitat loss, the pet trade, subsistence hunting, and capture for biomedical research. Throughout the 2010s, 60 percent of the more than 400,000 long-tailed macaques exported from Asia went to the US.

On paper, most long-tailed macaques imported by the US are labeled as captive-bred — meaning they came from facilities that breed them for research rather than from the wild. But some experts believe that illegal trade in wild-caught macaques is widespread, and that many of those that end up in US labs have actually been trafficked from the wild. In November 2022, the Department of Justice indicted eight people allegedly involved in a smuggling ring that brought more than 2,600 wild long-tailed macaques from Cambodia into the US under false permits labeling them captive-bred.

A group of long-tailed macaques hang from a wired ceiling in a fenced-in outdoor area.
Long-tailed macaques at a breeding facility in Vientiane, Laos.
Jo-Anne McArthur/We Animals Media
A monkey cradles a small baby monkey against the backdrop of a concrete wall.
A long-tailed macaque mother and infant at a breeding facility in Vientiane, Laos.
Jo-Anne McArthur/We Animals Media

Then last April, amid growing concerns about the species, a coalition of animal rights activists, conservation groups, and scientists led by People for the Ethical Treatment of Animals (PETA) petitioned the federal government to list the long-tailed macaque under the Endangered Species Act.

This could have radical implications: If successful, their call might not only end imports of long-tailed macaques, but also help address the physical and psychological distress they face in US testing labs and perhaps even end their use in research altogether. And it could do that for all members of the species — whether they were abducted from the wild or have lived their whole lives in a cage.

The Endangered Species Act’s radical potential for animals in captivity

The PETA-led petition’s potential to upend a pillar of biomedical research in the US highlights what may be an underappreciated aspect of the Endangered Species Act (ESA), a landmark federal law passed 50 years ago last month to protect species at risk of extinction. While its most high-profile successes include such symbols of the American frontier as the bald eagle, the Florida panther, and the grizzly bear, the law is not just for protecting animals in wild habitats from human encroachment. It also calls for better treatment of endangered animals in captivity.

Although the exact status of captive animals under the ESA is far from settled — subject to shifting regulation, controversial loopholes, and evolving case law — its wide-ranging protections promise to free endangered animals from many forms of exploitation that are beyond the reach even of laws ostensibly designed to stop animal cruelty. The 1966 Animal Welfare Act, for example, merely sets minimal standards for the conditions of animal use, such as minimum cage sizes for animals used in experiments — thereby taking for granted that animals will be harmed for profit-seeking purposes like entertainment, drug development, or cosmetic testing.

But the ESA provides a basis for challenging such harm. It prohibits any “take” of an endangered animal, which the law defines as “to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct.” It also allows citizens to directly sue entities that they believe are violating the law, making it much easier to enforce than the Animal Welfare Act.

In conservation biology, the health of wild animal populations and the welfare of animals held in captivity for human purposes have traditionally been seen as incompatible, or at best unrelated — contributing to a divide between conservationists and animal rights advocates.

Animal advocates are often highly critical of zoos and aquariums, for example, because of the physical and psychological harm that can be inflicted on animals confined to small, unnatural settings. Those most concerned with the survival of wild populations, however, sometimes support zoos because they help keep the species’ gene pool alive (whether zoos actually help wild animal populations, however, is contested).

Michael Soulé, considered a founder of conservation biology, wrote in 1985 that the field was not concerned with “the welfare of individuals,” but only with “the integrity and continuity of natural processes.” While he objected to animal cruelty, he cautioned that “conservation and animal welfare … are conceptually distinct, and they should remain politically separate.”

But in the Endangered Species Act, these two goals — protecting species and protecting individual animals — are linked. “The language, purpose, and legislative history of the ESA … make clear that the act is designed to protect both captive and wild members of protected species,” wrote legal experts Delcianna Winders, Jared Goodman, and Heather Rally in a chapter of the 2021 edition of Endangered Species Act: Law, Policy, and Perspectives. According to Sanerib, that’s part of what makes it one of the stronger environmental laws on the planet.

A key ESA case for captive animals began to take shape in the late ’80s, about as far from wilderness as you can get: backstage on the Las Vegas Strip. A dancer at Vegas’s Lido de Paris cabaret leaked footage to PETA showing famed animal trainer Bobby Berosini beating the show’s performing orangutans. Subsequent investigation found further evidence of physical and emotional abuse, including cage sizes roughly one-third of the legal requirement. Attorney Katherine Meyer, who led PETA’s case against Berosini, argued that the orangutan operation wasn’t just a typical animal cruelty case: Because orangutans were listed as endangered, Berosini was violating the ESA.

Berosini’s permit to breed the endangered great apes was revoked, and the show closed down. Meyer, who later became the inaugural director of the Harvard Animal Law and Policy Clinic, said this was the first case she knows of in which the ESA was used to protect captive animals from abusive situations. In the decades since, ESA lawsuits have been brought against the Ringling Bros. and Barnum & Bailey Circus, the Miami Seaquarium theme park, and numerous roadside zoos, on behalf of endangered bears, elephants, orcas, and other captive animals.

The exact scope of the law’s protections remains a legal gray area, Delcianna Winders, a professor and director of the Animal Law and Policy Institute at Vermont Law and Graduate School, told me. Some courts have decided that poor living conditions or inadequate veterinary care constitute a “take” under the ESA, leading to several closures of roadside zoos. In 1976, Winders added, Congress rejected an amendment to the ESA pushed by the animal exhibition industry that would have excluded the “ordinary activities of a zoo, circus, menagerie or other similar exhibition” from the law’s purview.

But exemptions have been written into the law to exclude Animal Welfare Act-compliant practices from the definition of “harassment” — making it harder to argue in court that confining elephants in zoos, for example, is inherently an illegal form of harassment under the ESA.

“It’s been a decades-long series of trial and error” to figure out how the ESA should treat captive animals, Winders said, and some tension remains.

How the Endangered Species Act freed chimps from lab testing

Although the ESA doesn’t outright ban keeping endangered animals in captivity, its prohibitions on what you can do to a captive animal are far more stringent. The law poses a direct challenge to animal testing, which, according to Winders, clearly constitutes a “take.” Invasive experimentation almost definitionally involves the harm, wounding, and often killing of an animal.

While the ESA makes it difficult to experiment on an endangered animal, it is not impossible. Facilities can still carry out such research by obtaining a special permit from the Fish and Wildlife Service (FWS), the federal agency that enforces the Endangered Species Act. In theory, to qualify for a permit, the research is supposed to benefit the species writ large, but in practice, the FWS has established what critics call a “pay-to-play” system: Researchers are allowed to simply donate to the conservation of a species in the wild in exchange for permits to conduct experiments on captive members of that species.

These arrangements have become common. In Atlanta, for example, the federally funded Emory National Primate Research Center experiments on the sooty mangabey, an endangered West African monkey held for research on HIV/AIDS, immune function, and other subjects.

In 2016, Reuters reported that over the previous five years, “the vast majority of the estimated 1,375 endangered species permits granted by the Fish & Wildlife Service involved financial pledges to charity.” In a typical example, the agency approved a permit to transfer endangered African penguins to Miami Seaquarium in exchange for a $5,000 pledge to penguin conservation in South Africa. Following Vox’s interview requests, the FWS did not provide comment.

Despite that loophole, invasive research on endangered species remains rare and faces significant hurdles. In fact, the ESA has already succeeded in freeing one iconic species from such research: our social, tool-making, highly intelligent cousin, the chimpanzee.

Until quite recently, chimps’ genetic proximity to humans was seen as a reason to experiment on them rather than to protect them from captivity and exploitation; they were used around the world to study infectious diseases such as HIV and hepatitis. But in the late ’90s and early aughts, a growing global movement for chimpanzee rights resulted in bans on using them (along with other great apes, including bonobos, gorillas, and orangutans) in invasive experiments in countries around the world.

By 2013, nearly every country that had been using chimps in invasive medical research had ceased the practice — with the US a notable exception, even though chimps were, and still are, endangered in the wild.

That was made possible because, for many years, wild chimpanzees and captive chimpanzees were treated differently under the Endangered Species Act. The former were listed as endangered, while the latter were considered only “threatened” — a less severe classification that made it easier to allow the continued “take” of captive chimpanzees.

Chimps were the only species subject to this “split listing,” which, the Fish and Wildlife Service explained in 1990, was due to their “importance in biomedical and other kinds of research” and their “use by zoos, as pets, and in entertainment.”

To Katherine Meyer, the split listing seemed unlawful. In 2010, she consulted with Anna Frostic, an attorney for the Humane Society of the United States, who submitted a petition co-signed by the Jane Goodall Institute, the American Association of Zoological Parks and Aquariums, and several other groups urging FWS to classify all chimps as endangered, including captives.

Five years later, their effort succeeded. While some in the research industry lamented this decision, they failed to mount a serious opposition. By November 2015, the National Institutes of Health (NIH) announced it would no longer support chimpanzee research, ending a 90-year era of invasive research on our closest relatives.

A cage stands on dirt ground outdoors amid greenery.
A cage once used to house chimpanzees used for research. It now stands empty in Carignan, Québec, at the entrance to the Fauna Foundation, an organization that provides sanctuary to chimps and monkeys formerly used in biomedical research.
Jo-Anne McArthur/We Animals Media
A chimp sits on a fence against a backdrop of open greenery.
A chimpanzee rescued from experimentation lives at Save the Chimps, a chimp sanctuary in Florida. The organization was founded in 1997 to house chimpanzees used by the US Air Force in space travel research and has since taken in hundreds of chimps rescued from biomedical research.
Jo-Anne McArthur/New England Anti-Vivisection Society/We Animals Media

At the time of the petition, Congress had already been considering a bill to ban invasive research on great apes, citing the animals’ intelligence, social nature, and psychological needs. The scientific merit of experiments on chimps had also been thrown into doubt: A 2011 NIH report found that “most current use of chimpanzees for biomedical research is unnecessary” (though it did not endorse a ban). The FWS’s 2015 decision was the final — and critical — nail in the coffin for the practice.

The case against split listing succeeded, Meyer said, because of the inherent connection between protecting captive animals and helping their wild counterparts. Jane Goodall and other experts argued that the use of captive chimps undermined conservation in their native range. It’s hard to ask poorer African countries to conserve chimps, Meyer explains, “when we’re hypocrites, we’re exploiting the captive members [of the species] in all kinds of ways.”

A scientific reckoning over primate testing

The same is even more true of long-tailed macaques. Experimenting on them not only undermines US endangered species policy by creating the appearance of hypocrisy, but it also contributes directly to the species’ decline, incentivizing the illegal capture and sale of wild macaques. That has put the long-tailed macaque at the center of a reckoning within the scientific community over the exploitation of endangered animals.

According to the IUCN, the current level of long-tailed macaque exports is “considered by trade monitors as ‘extremely unsustainable,’” putting “a significant strain” on the species’ wild populations. The IUCN raised the concern that breeding facilities in Southeast Asia, motivated by “the large amount of money that can be made in the trade,” can illicitly label wild-caught macaques as captive-born, then export them to countries with large biomedical research industries, such as the US and Japan. This allows exporters to sell more macaques without the time, difficulty, and expense involved in breeding them.

“There’s so much money in this; it’s too tempting to break the law,” said Jeremy Beckham, former research advocacy coordinator for the Physicians Committee for Responsible Medicine. So long as research facilities in wealthy countries are willing to buy these animals, he argues, that is “going to incentivize dishonest actors” to take them from the wild — just as, the Department of Justice alleges, has been happening in Cambodia. The DOJ declined to comment on the ongoing case.

The 2022 DOJ indictment has had cascading effects on the research industry: In the aftermath, the US has halted nearly all primate shipments from Cambodia, which had previously provided nearly 60 percent of primate imports. In March 2023, the Guardian reported, the fate of more than 1,000 macaques held by pharmaceutical company Charles River Laboratories, the largest US user of nonhuman primates, was in limbo, as they cannot be experimented on unless it is proven they were truly captive-bred.

For now, the macaques remain in Charles River’s custody, and the company told Vox that it has suspended primate shipments from Cambodia “until such time we and the U.S. Fish and Wildlife Service can develop and implement additional procedures to reasonably ensure confidence that the NHPs [non-human primates] we import from Cambodia are purpose-bred.”

The situation has raised alarm bells for biomedical researchers, who complain of a “shortage” of laboratory primates. In July, Charles River and various industry groups drafted a statement calling for increasing domestic capacity for breeding long-tailed macaques, so that the US doesn’t have to rely on primates imported from abroad.

Meanwhile, the National Association for Biomedical Research (NABR), a trade association defending animal research, alleges that the IUCN’s classification of long-tailed macaques as endangered got it wrong, and that the species is in fact thriving. An NABR-funded study published last December found “no data” supporting species decline, and the organization has formally challenged the IUCN’s listing. Craig Hilton-Taylor, head of the IUCN Red List Unit, confirmed that the organization is considering NABR’s petition, and said the evidence will be reviewed by an independent committee.

Many scientists who study primates in the wild see things differently. “All of us who work in the field and have the opportunity to study wild primates can see the impact of laboratory research on wild populations,” primatologist Ángela Maldonado, legal representative at the Colombia-based NGO Entropika and a signatory of the petition to protect long-tailed macaques under the ESA, told me. While she “respect[s the] research and studies” of those who work with captive primates, she believes that “when someone gets a monkey in a lab, and never saw them in the wild, it’s very difficult to understand the ethical and behavioral impacts on animals.”

The International Primatological Society recently called for an end to experimentation on wild-caught primates, and urged scientific journals to refuse to publish research conducted on them. “It is essential that in our quest to protect and improve human health, we do not lose sight of the importance and the inherent value of wild primate populations,” wrote the working group that drafted the statement.

The research industry, for its part, stresses the importance of invasive experimentation for human health. “Nonhuman primates ... play a critical role in developing new drugs, devices and vaccines,” said NABR president Matthew R. Bailey in a press release last summer. “Arbitrary restrictions imposed on the importation of long-tailed macaques could jeopardize millions of human lives and threaten global public health.”

But both the necessity and the ethics of using primates in medical research are highly contested, including by some scientists. Former animal researcher Garet Lahvis argued in Vox last year that lab monkeys are so severely psychologically damaged from being confined in tiny cages as to make them virtually useless as test subjects. Neurologist Aysha Akhtar, a former medical officer for the Food and Drug Administration and now a fellow at the Oxford Centre for Animal Ethics, argues that our reliance on animal testing ends up hurting humans by producing “misleading safety studies, potential abandonment of effective therapeutics, and direction of resources away from more effective testing methods.” In 2022, Congress passed a law removing the requirement for new drugs to be tested on nonhuman animals.

The long-tailed macaque’s fate hinges on the ESA. What about other animals used in experiments?

Biomedical researchers and animal advocates do agree on one thing: an ESA listing for the long-tailed macaque could transform the species’ use in US labs.

Without external pressure, however, the Fish and Wildlife Service is unlikely to announce protections for long-tailed macaques any time soon. One 2011 paper looking at 130 animal species listed as endangered by the IUCN found that more than half were not recognized by the Endangered Species Act.

The reason for that gap, lead author Bert Harris wrote in an email, is that “the ESA is perpetually bogged down by politics. For example, the number of listings that are done each year changes dramatically when new presidential administrations take over.”

A more reliable (though still not guaranteed) path to getting a species ESA protection is to directly petition the FWS — as the PETA-led coalition did for long-tailed macaques last April. The same day, they put forward a similar petition for the southern pig-tailed macaque, which was also listed as endangered by the IUCN but is used in lab testing (albeit much less commonly) in the US. Both petitions await a reply from the FWS.

Two adult pig-tailed macaques and one infant surrounded by greenery. One of the adults has their hand on the infant’s back.
Southern pig-tailed macaques in the rainforest in Sepilok, Sabah, Borneo, Malaysia.
Stephanie Rabemiafara/Getty

While FWS is supposed to provide at least a preliminary response within 90 days, this has not happened, and experts say the process typically drags on much longer. It often takes years after an initial petition for a species to get Endangered Species Act protection. Politics within the scientific community may factor into the FWS’s decision, too: While chimp experimentation was already on the way out by the time they were listed under the ESA, research on long-tailed macaques is still in very high demand.

Still, “given that long-tailed macaques are considered endangered by IUCN and are in trade to and within the United States, there is a good chance FWS will list them under the ESA” — eventually, said Tanya Sanerib of the Center for Biological Diversity, who was not involved in the petition.

The Fish and Wildlife Service might decide to list the macaque as merely threatened, Winders explained, which would give the agency some leeway in deciding whether experimentation on the species should continue. If it lists the macaque as endangered, however, invasive research might end entirely.

According to Amy Meyer, manager of PETA’s primate experimentation campaigns, research on long-tailed macaques is unlikely to get the sort of “pay-to-play” treatment applied to research on endangered sooty mangabeys. The permit for sooty research allows only “limited invasive sampling, including anesthetizing, collecting blood, skin, and bone marrow tissue samples, and MRI scanning” — “still cruel,” Meyer said, but long-tailed macaques used in labs are regularly exposed to high levels of toxins and chemicals, resulting in poisoning and death, a different scale of harm to the animal.

For animal advocates, the Endangered Species Act’s potential is doubled-edged. It offers some animals protection against cruelty arguably stronger than what’s found anywhere else in US law, but only if they’re endangered. It’s not the harm itself that matters — the caging, poisoning, vivisecting, or killing — but whether that harm affects the survival of wild populations. While this could buy some relief for the long-tailed macaque, the ESA will remain indifferent to the vast majority of laboratory animals, which are members of non-endangered species such as mice and rats.

Three adult macaques sit asleep in a row on a fence in a forest while cradling an infant macaque.
Sleeping mother and infant long-tailed macaques in the Alas Kedaton Monkey Forest in Bali, Indonesia.
Martin Harvey/Getty Images

Still, according to Beckham, campaigns to help primates such as long-tailed macaques can help break down the moral barrier that people put between humans and other animals. “If we can ... get people to understand we shouldn’t be using monkeys in laboratories, it is probably just the next logical step that people will start to think about dogs, and then rabbits, and then rats.”

The long-tailed macaque, like the chimpanzee before it, might be an especially good candidate for breaking down that barrier. These monkeys “love to swim,” said Amy Meyer. “I’ve watched videos where they literally are climbing up trees just to jump in water. They like to have fun. [They are] social.”

In other words, she said, “You look into their eyes and you see ourselves.”

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