In the late 1990s, Jaak Panksepp, the father of affective neuroscience, discovered that rats laugh. This fact had remained hidden because rats laugh in ultrasonic chirps that we can’t hear. It was only when Brian Knutson, a member of Panksepp’s lab, started to monitor their vocalisations during social play that he realised there was something that appeared unexpectedly similar to human laughter. Panksepp and his team began to systematically study this phenomenon by tickling the rats and measuring their response. They found that the rats’ vocalisations more than doubled during tickling, and that rats bonded with the ticklers, approaching them more frequently for social play. The rats were enjoying themselves. But the discovery was met with opposition from the scientific community. The world wasn’t ready for laughing rats.

That discovery was just the tip of the iceberg. We now know that rats don’t live merely in the present, but are capable of reliving memories of past experiences and mentally planning ahead the navigation route they will later follow. They reciprocally trade different kinds of goods with each other – and understand not only when they owe a favour to another rat, but also that the favour can be paid back in a different currency. When they make a wrong choice, they display something that appears very close to regret. Despite having brains that are much simpler than humans’, there are some learning tasks in which they’ll likely outperform you. Rats can be taught cognitively demanding skills, such as driving a vehicle to reach a desired goal, playing hide-and-seek with a human, and using the appropriate tool to access out-of-reach food.

The most unexpected discovery, however, was that rats are capable of empathy. Since the 1950s and ’60s, behavioural studies have consistently shown that rats are far from the egoistic, self-centred creatures that their popular image suggests. It all began with a study in which the rats refused to press a lever to obtain food when that lever also delivered a shock to a fellow rat in an adjacent cage. The rats would rather starve than witness a rat suffering. Follow-up studies found that rats would press a lever to lower a rat who was suspended from a harness; that they would refuse to walk down a path in a maze if it resulted in a shock delivered to another rat; and that rats who had been shocked themselves were less likely to allow other rats to be shocked, having been through the discomfort themselves. Rats care for one another.

But the discovery of rat empathy was also met with incredulity. How could a rat be empathic? Surely, there must have been something wrong with the experimental procedures. So the rat empathy research programme languished for some 50 years. The world was no more ready for empathic than for laughing rats.

In 2011, the issue of rats’ empathy resurfaced when a group of scientists found that rats will reliably free other rats who are trapped inside a tube. It was not that they were merely curious or wanted to play with the apparatus: if it was empty or contained a toy rat, they would tend to ignore it. And the tube wasn’t easy to open – it required effort and skill – so it seems that the rats really wanted to free their fellow rat. Most scientists were not convinced, suggesting instead that the rats probably just wanted someone to hang out with, or that they found it annoying that the trapped rat was making such irritating noises and wanted it to stop. The rats, according to these scientists, were not acting out of concern for the other, but out of pure egoism. What else could one expect from a rat?

While this sort of skepticism is usually praiseworthy in scientists, it has been bad news for rats. Since that 2011 experiment, there has been an explosion of different studies that continue to place rats in harmful situations to see if others will help them. They find the same pattern: rats are more likely and quicker to help a drowning rat when they themselves have experienced being drenched, suggesting that they understand how the drowning rat feels. Rats will also help a trapped rat even when they can escape and avoid the situation, something many humans fail to do. The results of these studies are compelling, but they don’t show us much more than what we already suspected from the work done in the 1950s and ’60s – that rats are empathic; meanwhile, the studies have inflicted, and continue to inflict, significant fear and distress on the rats.

The explicit goal of this research is to create mentally ill, traumatised, emotionally suffering rats

Scientists are willing to continue harming rats because they are seen as a cheap and disposable research tools. In the US, rats are not covered by animal welfare laws: scientists can legally do whatever they want to them. This is true of how rats are acquired, housed, manipulated and killed. Even though scientists have found that killing rats using carbon dioxide causes unnecessary distress, this continues to be a popular method for disposing of them once their usefulness has ended. And there are other methods. The scientist John P Gluck, in his book Voracious Science and Vulnerable Animals (2016), describes how he was taught to euthanise rats when the chloroform ran out:

[My supervisor] took a large male rat in his hand, turned to face the brick parapet wall that followed the edge of the building, reared back, and threw the rat at the wall like a baseball pitcher throwing a fastball. The rat made a pop as it hit the wall, fell straight down onto the gravel-covered roof, quivered, and then lay totally still in the shadow of the wall.

Scientists are now tinkering with rats’ empathy in order to find ways of treating human psychopathologies. In some cases, rats are given treatments that temporarily disable their empathic capabilities, such as anxiolytics, paracetamol, heroin or electric shocks. In other cases, the harm is permanent. Rats are separated from their mothers at birth and raised in social isolation. In some studies, their amygdalae (the brain area responsible for emotion and affiliation) are permanently damaged. The explicit goal of this research is to create populations of mentally ill, traumatised, emotionally suffering rats.

While there are worries about these experiments from a welfare perspective, there are deeper worries from ethical perspectives that respect the autonomy of the individual. These experiments are turning healthy, empathic individuals into callous psychopaths. This is a deep violation of the integrity of a psychological agent. Still, these studies are justified as ways of creating animal models of childhood maltreatment, psychopathy, social functioning deficits in opioid addiction, anxiety and depression, conduct disorders and callousness, all of which would ideally help us later to treat these conditions in humans.

The logic behind these studies is paradoxical: rats are close enough to us to serve as models for human psychopathologies, but far enough to be outside of ethical concern. Researchers today would hardly dream of creating human psychopaths to study, or showing a human subject a real drowning child in order to offer a chance to rescue. The reason is simple: humans have an empathic nature that ought to be respected. But we do it to rats, despite their own empathic nature.

In fact, we’ve done it before – to primates. Until they were protected by welfare legislation, researchers treated primates much as rats are treated today. Some rat research is even recapitulating the most morally fraught episode in the history of primate research: Harry Harlow’s maternal deprivation and social isolation studies of the 1960s. For decades, Harlow created psychologically damaged primates in order to better understand human psychopathologies. Monkey babies were separated from their mothers for six to 12 months so that he could study the effects of breaking the maternal bond. Juveniles were isolated in what Harlow called the ‘pit of despair’: a tiny metal cage meant to induce depression in otherwise healthy and happy monkeys. It worked all too well.

In Voracious Science and Vulnerable Animals, Gluck writes about what it was like working in Harlow’s lab at the University of Wisconsin-Madison as a PhD student. Even when students proposed a ‘sadistic little project’ of blinding and deafening infant monkeys to see how their mothers would raise them, Gluck says that Harlow never raised a single ethical concern. The research was justified so long as it offered benefit to humans, despite Harlow’s own findings that monkeys are ‘self-conscious, emotionally complex, intentional, and capable of substantial levels of suffering’. Creating and then treating monkeys with psychiatric disorders such as depression was seen as offering benefit to humans, and that fact alone justified the research.

As our closest living relative, chimpanzees were also subject to decades of medical research before governments decided to ban such studies. Chimpanzees were infected with hepatitis and HIV, but were also used to test insecticides and cosmetics, and were injected with industrial drycleaning solvents and benzene.

In his memoir Next of Kin: My Conversation with Chimpanzees (1997), Roger Fouts – who started working with these chimpanzees as a graduate student – tells of visiting one ‘old friend’ at LEMSIP, a biomedical lab run by New York University. The chimpanzee Booee had grown up signing to Fouts and to other chimpanzees but, when the project funding ran out, Booee was sent to LEMSIP, infected with hepatitis C, and kept alone in a cage. Fouts reports that he tried to help Booee and the other chimpanzees he’d worked with, and his failures took an immense personal toll on him, leading to alcohol abuse and a deep depression.

Chimpanzees were excused from biomedical research because they are seen as almost human

Years later, when a producer from the TV show 20/20 got in touch and asked if he would reunite with Booee in front of the cameras, Fouts was hesitant, but he thought he owed it to Booee to tell his story on national television. The clip is on YouTube now, and it shows Fouts walking ape-like into the lab, panting in a typical chimpanzee gesture, and approaching Booee’s cage while signing ‘Hi Booee, you remember?’ Booee remembered, signing back his old nickname for Roger – ‘Rodg’ – and then asking for food and for games of chase and tickle. But when it came time for Fouts to leave, Booee moved to the back of the cage and refused to say goodbye. He was hurt.

Today, the situation for primates has improved. In 1985, the US research landscape changed with substantial amendments to the Animal Welfare Act, requiring all institutions that use animals to create formal Institutional Animal Care and Use Committees to oversee and regulate the use of warm-blooded animals in research (except for birds, mice and rats). Chimpanzee welfare, while by no means perfect, is even better. In 2010, the US National Institutes of Health (NIH) commissioned a study by the Institute of Medicine to determine whether chimpanzee biomedical research offers a public good. In their report, the committee concluded that ‘while the chimpanzee has been a valuable animal model in past research, most current use of chimpanzees for biomedical research is unnecessary’. This led in 2015 to the effective end of all biomedical research in the US, 14 years after Europe ceased its chimpanzee research programmes.

While the NIH instructed the Institute of Medicine committee to eschew any ethical considerations in their recommendation, they were apparent in their report. Chimpanzees were excused from biomedical research because they are seen as exceptional animals, as almost human. The study argued that animals that are closely related to humans ought not be used for research when less closely related animals could be used instead. The use of chimpanzees has a ‘moral cost’.

In announcing the decision to end the era of using chimpanzees as research subjects, the NIH director Francis Collins repeated these ideas, explaining that chimpanzees are ‘special animals, our closest relatives’ whose DNA is ‘98 per cent … the same as ours’. In the US, chimpanzees are mostly being retired to federally funded sanctuaries designed to support their interests. Given their special status, approval for research on the private chimpanzees still held in the US will require proving that the research will benefit wild chimpanzees.

Protections for monkeys are moving in the same direction. Today’s young primate scientists have (mostly) been trained to see the ethical problems of the maternal deprivation and social isolation research programmes, and to see their monkey subjects as social beings who can thrive and suffer. When researchers are finished with their monkey-research projects, they look for sanctuaries to send them to. These movements toward making monkey retirement a norm follow the same logic as the chimpanzee studies. Monkeys are intelligent, social and emotional beings, and not merely a byproduct of scientific investigation. When their usefulness in science is finished, they should be cared for with their interests at the forefront. It’s the right thing to do.

The same does not hold for rats. In fact, their use in labs is increasing. Since lab rats are not considered to be animals deserving of protection, there are no official statistics on the numbers of rats used in the US. Estimates range from 11 to 100 million used in the US alone, with almost all of them being killed once their usefulness is over.

What accounts for this difference in treatment and protection between primates and rats? The question itself might seem odd because the answer is so obvious: chimpanzees are our closest living relatives, and apes and monkeys look like humans. We are fascinated by reports of wild primates, and the scientist most known for studying chimpanzees – Jane Goodall – is a folk hero. There isn’t a famous rat researcher. There isn’t a famous rat whose story has been told in film, television or books, in contrast with Digit (Diane Fossey’s favourite gorilla), David Greybeard (the first chimpanzee who made contact with Jane Goodall at Gombe Stream Research Centre), Washoe (the chimpanzee who learned American Sign Language signs from Roger Fouts), Ai (the chimpanzee scientist Tetsuro Matsuzawa calls his ‘research partner’), Kanzi (the bonobo Sue Savage-Rumbaugh taught to comprehend spoken English at the level of a three-year-old human), or Nim Chimpsky, studied by Herbert Terrace and star of Project Nim (2011).

In many ways, the current science vindicates the popular view of chimpanzees (as well as other apes and monkeys). Chimpanzees are intelligent tool users who create new technologies for accessing food and for communication. Chimpanzees live in territories that they fight for and defend. Chimpanzees are a cultural species, and chimpanzee immigrants adopt the practices of their new community, even when those new practices are less efficient than their old ones. Chimpanzees have personalities, they have relationships, and they help take care of one another. One of us has argued that chimpanzees have a form of moral agency, and the other has argued that they can be considered normative agents who live by and support social norms. Chimpanzees are amazing. But rats are pests.

It is almost a truism to say that humans don’t like rats. If we were to list the animals that generate the strongest distaste in us, rats would be very near the top. The ones that populate Western cities are viewed as vermin, with such worthless lives that we don’t give a second thought to attempts to eradicate them. A recent article in the online magazine The Conversation raised the concern that rat-population management strategies might be unintentionally creating rats that are extremely fit or unusually prone to disease, but the logic was purely anthropocentric – the worry was that we might be creating rats that are even more dangerous and difficult to eliminate. Not only is there a lack of concern towards rats, these animals are often viewed as something we wish didn’t even exist. The presence of a rat is synonymous with dirt, disease, disgust. And a rat is one of the worst things you can call someone.

This general lack of concern towards rats is mirrored in their use in biomedical research. Rats, together with mice, have long served as the leading model organism, given their large brains, ease of handling and housing, and biological and behavioural similarities to humans. Rats are cheap and easy to use. Unlike primates, they are easily bred, easily obtained through mail order, and easily housed in individual boxes at the lab. They also come with further advantages when compared with primates, such as the fact that their gestation periods are much shorter and they have a larger number of offspring, and that they reach maturity much quicker and have much shorter lifespans.

Rats need an ambassador, a Jane Goodall figure who can present rats as individuals

The rat genome was fully sequenced in 2004, which has allowed for significant advances in our understanding of how genes work. Their relatively bigger size when compared with mice has also made them an ideal model for cardiovascular research, and allowed us to advance in our understanding of obesity, diabetes and cardiovascular diseases. They are preferable to mice for behavioural and psychological studies because they have a more social nature that better mimics our own. All of these advantages make it difficult to question the use of rats in biomedical research. However, no species would be a better research subject for advancing human medicine than our own, and here we are perfectly capable of understanding that there are certain moral limits that cannot be crossed, no matter what possible gains might come of it.

Perhaps what rats need is an ambassador, a Jane Goodall figure who can tell the stories of their lives, and present rats as individuals, rather than as the referent of a generic-count noun. While there are rat advocates out there, they don’t get much attention. The UK has its National Fancy Rat Society, which was formed in 1976, and calls itself ‘the club for everyone who appreciates the rat for what it is – a superior pet and fancy animal’. In 1983, the US got its own American Fancy Rat and Mouse Association. These organisations have regular exhibitions and competitions and judge rats on their match to a variety of standards or their personalities. Rat agility is now an international sport, and YouTube is rife with videos of rats running tiny courses. However, the Westminster Kennel Club these are not. You won’t hear the results of any rat show competitions on the local news.

APOPO, a Belgian NGO, celebrates ‘HeroRats’ who have saved countless lives by identifying landmines left over from wars and conflicts around the world. ‘Those rats scuttled about, sniffing here and there, and then they would stop, smell the air, and then scratch the ground. That means they found a landmine!’ said Lann Sa, a Cambodian farmer who had already lost one leg to a landmine. ‘Less than two weeks later, our fields were free of landmines. Our kids were safe, our fields full of growing crops.’ The rats are hand-raised by humans from infancy and trained to expect a treat when they smell TNT. The African giant pouched rats that APOPO works with are (despite their name) too light to set off the landmines, and they have suffered no losses in their work. After several years of labour, the rats enjoy retirement in their home cage, with play, snacks and socialisation with humans. The rats have different personalities and different preferences. ‘Shuri’, a HeroRat featured on APOPO’s homepage, ‘is a staff favourite with a cheeky personality who brings a smile to the face of everyone she meets.’ Her preferred snack is a peanut.

When we take the time to step back and treat rats as individuals – as Fouts did with Booee and Goodall did with David Greybeard – we can come to see rats not as research tools, but as sentient beings who have the capacity to enjoy rich emotional lives. As researchers found out more about primates, they realised that primates required protection, leading to welfare legislation and oversight committees. However, as we find out more about rats, rather than changing the way we treat them, science is repeating the mistakes made in the early days of primate research. Harlow’s ethically questionable logic was that monkeys are similar enough to humans to be used as models for human mental disorders, but not similar enough to warrant the same levels of protection from harm. The justification for the rat research is that rats are similar enough to humans to serve as good models of human health, including mental health, but not similar enough to warrant any legal protection from harm. Some scientists even welcome this lack of care toward rats, who with other rodents are considered to ‘offer a cheap, convenient and ethically less controversial alternative to non-human primates in the study of social cognition’. While the free use of rats in research might be less ethically controversial than the use of primates – given the relative lack of rat ambassadors – it is not more ethically justifiable.

It is understandable to make an ethical mistake once. But, after realising the error, we should be better prepared to see the problem in new cases. Moral progress depends on realising that two cases are alike in morally relevant ways. The failure to generalise from one case to another can lead us to continue making the same ethical mistakes in new contexts. We cannot deny the moral costs of creating psychopathologies in rats in order to treat psychopathologies in humans, while weighing those costs and condemning the practice in primates. The very similarity that is appealed to in justifying the science – that primates are vulnerable to physical and mental pain, that they have emotions and relationships that can be destroyed when they are denied normal maternal care – is what creates the moral cost of creating those harms. These moral costs exist in the case of rats too. It is only our moral short-sightedness and relentless anthropocentrism that have prevented us from taking them into account.