The Intriguing New Science That Could Change Your Mind About Rats

Posted by Big Rat on Campus on Feb 4, 2015 in Rat News | Subscribe

Rats like this one, in the laboratory of neuroscientists Peggy Mason and Inbal Ben-Ami Bartal, are teaching us a lesson about the nature of empathy. Brandon Keim/WIRED

Many people live among animals that inspire affection, even admiration: bluebirds and hawks, beavers and bobcats. The fortunate might glimpse a fox or, if they live in the country, an eagle or a bear. But I live in New York City, where the star of the show is the rat.

Pity the rat. Few mammals are so reviled in western culture, so deeply and viscerally loathed, as Rattus norvegicus. Regarded less as animals than as rapacious, beady-eyed vectors of filth and disease, they can drive otherwise warm-hearted souls to fantasies of extermination. Rats on an abandoned ship, to take a recent example, aren’t pitied as starving; they’re reviled as cannibals.

Yet even those who recoil at the sight of a hairless tail often grant rats certain respect. Despite centuries of ruthless extermination, R. norvegicus has withstood everything we’ve thrown at it and come back for more. Above all, they are survivors. A rat foraging on a subway track, thriving on what we discard and overlook, has a certain outlaw charm.

Often I’ve found myself considering what scientific questions might be asked of these supposedly lowly creatures. Plenty of people ponder consciousness in whales, or wonder what life looks like to a chimpanzee or a cat. But what about rats?

Unexpected as it might seem, we still have much to learn about rats, and from them. Yes, there’s volume upon volume of rat research—but most of it focuses on traditional questions of basic physiology and drug responses and so forth. Few researchers have asked what rats think and feel, or how they’ve adapted to environments so very different from their ancestral home in southern Mongolia.

On this front, rats are guides to emerging questions of evolution and cognition: how cities shape the brains and behaviors of the animals within them, and whether aspects of consciousness once considered exceptional might in fact be quite common.

Foremost among these is empathy, widely considered a defining human characteristic. Yet rats may possess it too. An especially fascinating line of research, the latest installment of which was published last year in the journal eLife, suggests rats treat each other in an empathic manner. Such thoughtfulness underscores the possibility that rats are far more complicated than we’re accustomed to thinking—and that much of what’s considered sophisticated human behavior may in fact be quite simple.

This idea runs contrary to notions of human exceptionality. Yet evolution teaches us that humans and other creatures share not only bodies, but brains. In that light, why wouldn’t rats care about each other? The idea also challenges us to see rats anew: Not just as vermin, or as anonymous laboratory models of some biological process, but as fellow animals.

As neurobiologist Peggy Mason, a pioneer in rat empathy research put it, “I’m perfectly happy thinking of myself as a rat with a fancy neocortex.”

On a table in Mason’s University of Chicago lab sits a plexiglass box about two feet square. Inside is a white Sprague-Dawley rat, a strain bred for laboratory study, and a plexiglass canister holding a black-and-white Long-Evans rat.

The trapped Long-Evans is clearly agitated. The white rat is too. Instinctively, she wants to stay in the corner; rats avoid open spaces, and navigate by touch, which is why you often see them scurrying along walls. Yet she rushes again and again to the canister, sniffing at the rat inside, nosing the glass, nudging the door. Eventually, she opens it, freeing the rat. They rub together.

At a purely descriptive level, you could say one rat helped another. Why that happened is the question. According to Peggy Mason and collaborator Inbal Ben-Ami Bartal, the free rat appears to empathize with her trapped comrade. She recognized the rat’s distress, grew distressed herself and wanted to help. This appears to be a powerful impulse in rats. In tests of whether rats would rather eat than help another rat, the researchers found empathy’s pull to be as strong as their desire for chocolate — and rats do love their chocolate.

The two researchers first claimed rats might feel empathy in a high-profile 2011 Science paper describing rats freeing their cagemates, rats they had been cohabitating with. They expand on those findings in the latest study, which describes rats helping strangers. It’s a radical, even controversial, claim. Some scientists recognize that chimpanzees, a few cetaceans and perhaps elephants could be empathic, but few have ascribed that trait to rats. If R. norvegicus can be empathic, that fundamentally “human” trait might in fact be ubiquitous.

“We’re in a period of transition with respect to how we think about animals,” said environmental philosopher Eileen Crist. After centuries of seeing the animal kingdom as a hierarchy with humans on top, of treating animals as purely instinct-driven biological machines, “cognitive ethology is opening up a new terrain. Knowledge itself is fluid and changing right now”—and empathy investigations are very much a part of that.

A free rat and a trapped cagemate in Peggy Mason and Inbal Ben-Ami Bartal’s lab.

A free rat comes to the aid of a trapped rat in Peggy Mason and Inbal Ben-Ami Bartal’s lab. Brandon Keim/WIRED

Those who’ve had pet rats may not be surprised by reports of their empathy, nor will readers of naturalists’ texts from the 19th and early 20th centuries. (Witmer Stone and William Everett Cram, for example, wrote of rats in 1902’s American Animals, “Careful witnesses have always given them credit for looking after any helpless member of their family….”) But informal observations carry little scientific weight, and researchers are reluctant to describe what animals might think and feel. After all, animals can’t tell us, and we can’t read their minds.

There’s some historical baggage, too. Twentieth-century study of animal behavior was famously inhospitable to the idea that animals feel much of anything. B.F. Skinner, the father of modern animal behavioral science, called emotions “an excellent example of the fictional causes to which we commonly attribute behavior.” Such views have largely fallen from favor, but science has been slow to embrace Charles Darwin’s essential point: that humans and other animals necessarily share not only anatomical roots, but neurological origins.

Claiming empathy for rats isn’t easy, and one criticism of Mason and Ben-Ami’s interpretation is that a far simpler phenomenon called emotional contagion could explain their rats’ helpfulness. In other words, when one rat becomes distressed, that distress spreads to others—but they don’t necessarily feel for the first and translate that feeling into intention.

As Oxford University zoologist Alex Kacelnik and colleagues noted in a 2012 Biology Letters reflection on empathy research, some ants display helping behaviors similar to Mason and Ben-Ami Bartal’s rats. “Any solid evidence for empathy in non-humans would be a notable advance,” they wrote, “but, in our view, it remains unproven outside humans.”

Other researchers defended the possibility of rat empathy. “Ants are not rats,” quipped Frans de Waal, an Emory University ethologist who has written extensively about empathy, on Facebook. “It would be totally surprising, from a Darwinian perspective, if humans had empathy and other mammals totally lacked it.” As for Mason and Ben-Ami Bartal, they’ve downplayed the empathy interpretation in their latest work, restricting it to speculative discussion.

In those experiments, they observed that rats helped not only their cagemates, but total strangers. They even helped strangers from other strains, like the Sprague-Dawley helping the Long-Evans, if they’d previously known a rat from that strain. Social experience mattered more than narrow biological self-interest. Regardless of whether that’s empathy, Mason and Ben-Ami Bartal hope the implications could extend beyond rats and provide a model system for investigating the basic biology of helpfulness.

“It’s our fervent hope that this model will be used by many researchers to look at helping behavior,” Mason said. “If we can see a way that rats can form an affective bond quickly, can we use that in society? Wouldn’t that be useful?”

Although she and Ben-Ami Bartal downplay the possible role of empathy, they still think it’s the most likely explanation for what they’ve observed. This argument isn’t just based on their experiments, but on evolutionary neurobiology. The brains of humans and rats are certainly not identical, but they overlap in fundamental ways. “We share the same neural structure with rats that we use for our own empathic responses,” said Ben-Ami Bartal.

The thing to remember, the researchers say, is empathy can take different forms. We often focus on its most sophisticated definition: the empathy that comes with, say, reading about the suffering of people far away and feeling compassion for them. So abstract a perspective is almost surely unique to Homo sapiens. But empathy can be much simpler, as when we instinctively want to comfort someone who’s crying. Most of what we consider human empathy, said Mason, takes this form, and needn’t be unique to us. It could exist in various permutations across mammals, as do its underlying evolutionary drivers and neurobiological processes.

Many well-regarded psychologists and neuroscientists have taken this position in recent years, arguing that simple empathy provides obvious evolutionary benefits for social animals, especially those species in which mothers care extensively for their young. Even complex, higher-order human empathy appears to stem from basic emotional and cognitive processes that rats—indeed, all mammals—certainly possess. “Evidence is accumulating that this mechanism is phylogenetically ancient, probably as old as mammals and birds,” de Waal wrote in a 2008 Annual Review of Psychology paper.

Jaak Panksepp, a Washington State University neuroscientist renowned for his research on rat emotions, says these lines of research raise a fascinating question: How are empathy’s various forms driven by simple mental processes, and to what extent do they involve complex, high-level cognition? If some forms of empathy can be quite simple, Panksepp says, the same could well apply to many other abilities long considered the sole province of humans.

One such ability, metacognition—the ability to think about thinking —already has been demonstrated in rats; as with empathy, simpler explanations could suffice, but the possibility is certainly there. Depending upon the sorts of memory and reasoning involved, rats also may be able to think symbolically; build mental models of their physical and social worlds; imagine themselves in the past and future; and communicate in a sort of proto-language, much like their prairie dog cousins appear to do. Such abilities would not be exactly like our own, but could resemble them far more than we generally think.

“Over the last few decades, comparative cognitive research has focused on the pinnacles of mental evolution, asking all-or-nothing questions such as which animals (if any) possess a theory of mind, culture, linguistic abilities, future planning, and so on,” wrote de Waal. “A dramatic change in focus now seems to be under way, however, with increased appreciation that the basic building blocks of cognition might be shared across a wide range of species.”

“We don’t have good data to adjudicate those issues, but I’d agree those are very important ones,” said Panksepp. “There should be an open conversation.” Mason puts it more bluntly. “There’s just no intellectual reason why we don’t share a basic underlying behavioral fabric,” she said.

A brown rat drinks from a stream in Manhattan’s Central Park. Brandon Keim/WIRED

To get a sense of how these questions might be playing out in the wild, I spent some time with Jason Munshi-South, a biologist at Fordham University. A self-described specialist in “evolution in the Anthropocene,” or the informal scientific name for an epoch profoundly shaped by human activity, he’s among the few scientists studying how city rats are evolving.

To better gather the tissue samples he uses to create population-genetic narratives of ecology and evolution, Munshi-South attended the exquisitely named NYC Rodent Academy. Taught by Robert Corrigan, who is generally regarded as the country’s foremost expert on rat control, the class opened a new dimension of the city. “It was like learning how to read the landscape,” Munshi-South said. “Everywhere I go, I see rat sign.”

We start our safari in an alley in lower Manhattan, not far from City Hall. We see no rats—it’s too cold, and there’s too much activity at an adjacent construction site—but their signs are everywhere. Munshi-South points out cracks between bricks and in foundations, barely noticeable yet unmistakably gnawed at their edge, entrances to tunnels leading to dens underfoot or behind walls.

We also see several of New York’s ubiquitous and, in the grand scheme of things, mostly pointless poison-bait boxes. Rat control is really food control, teaches Corrigan: As long as they have plenty to eat, rats will flourish. Cleaning up is hard to do, though, so instead we kill. Around one box are scattered nibbled pink bait blocks. They contain grain and potent blood thinners, and the rats who ate them probably bled to death.

Or maybe not. Many rat populations are becoming resistant to blood thinners, just as they adapted to previous rodenticides. Munshi-South wonders what specific resistance mutations have arisen within New York City’s rats, and how populations respond to eradication efforts. Rats in each neighborhood might descend from a few hardy survivors; or maybe new generations move in after previous residents die. These dynamics could affect how diseases ebb and flow in rats, and perhaps how humans are exposed to them.

Munshi-South suspects rats travel, like most New Yorkers, through subway tunnels, with genetic distributions displaying patterns of flow along the city’s main train lines. We leave the alley and walk to another favorite trapping site, the ancient Chambers Street/Brooklyn Bridge-City Hall station. Again he notes the telltale cracks in walls and along tracks. It’s easy to think they lead to an underworld rat metropolis, but of course they don’t. Rats stay close to food, and there’s plenty to be had here, a cornucopia of takeout boxes and illegally dumped trash.

Last summer, said Munshi-South, garbage bags piled at platform ends literally rippled with rats. Today they’re still. A rodenticide caution sign indicates a recent round of poisoning. Two earlier dates on the sign have been crossed out, testament to the ongoing struggle. When I return a few days later, a rat forages along the tracks. “My guess is that in here, they’ll never get rid of all of them,” he said.

Do these rats survive simply because they become resistant to poisons, and for the mechanistic reasons often invoked when discussing evolution: dietary habits, reproductive rates, adaptation to life underground? Those certainly play a part, but perhaps not the only one. Mental and social evolution—rats growing smarter, and perhaps more empathetic—could be a factor.

“What I’d imagine with rats, moving into a new environment and heavily persecuted, is that there’s selection on behavior that has a heritable basis, and especially on things like personalities,” Munshi-South said. He plans to compare the genomes of city rats and lab rats, and look for genetic changes linked to cognition. “I don’t think we know yet, but these are good hypotheses,” said Munshi-South.

Neophobia, or a temperamental inclination to avoid new objects, is one possible area of adaptation. Curiosity kills the rat, so to speak. Spatial memory enhancements could be useful in a landscape more complex than the rats’ ancestral plains. And empathy also could be key. One of its fundaments, an awareness of others how they feel, is integral to social learning: the ability to learn from others’ examples.

Not long ago I watched a pair of rats on the tracks of Brooklyn’s Hoyt-Schermerhorn station. One was a full-grown adult, the other hardly larger than a field mouse; mother and offspring, I assumed, with the young rat following closely in mom’s footsteps, perhaps learning lessons of life between the rails.

A brown rat forages on the subway tracks in Brooklyn's Hoyt-Schermerhorn subway station.

A brown rat forages on the subway tracks in Brooklyn’s Hoyt-Schermerhorn subway station. Brandon Keim/WIRED

Frans de Waal thinks empathy originated with maternal care, with evolution favoring those mothers most attentive to their offspring. Of course it could work in the other direction, too: Evolution favors offspring who pay attention to their elders. Rat mothers, it should be noted, are historically renowned for their devoted affection.

“Given the importance of social learning in rats,” said Emilie Snell-Rood, a biologist at the University of Minnesota, and its usefulness “in a situation where a novel predator like humans are trying to kill you all the time, I would expect increased selection on social learning.”

Empathy also could facilitate helpfulness, another potentially useful trait, and lead to diminished aggression: The more sensitive animals are to others’ emotional states, the more socially agreeable they tend to be. That’s been documented in animals living at high population densities, including chimpanzees, and urban rats are nothing if not populous.

Snell-Rood has studied how a century’s exposure to humans changed Minnesota’s small mammals. She hasn’t examined rats, but did document significant increases in brain size among other urban rodents, including squirrels, shrews and mice. That doesn’t mean the animals are getting smarter, but it does suggest something cognitive is going on.

Whether that involves empathy is an open question, a hypothesis to be tested. It is speculation of the sort encouraged by a 21st century appreciation of animal consciousness and evolution. Darwin would likely have enjoyed the possibilities. As he theorized in The Descent of Man, “those communities which included the greatest number of the most sympathetic members would flourish best, and rear the greatest number of offspring.”

In coming years, scientists could learn that R. norvegicus, which arrived in New York late in the 18th century, has taken an unexpected path to prosperity. Maybe city rats are kinder and gentler, at least with one another. It would make for a nice lesson. And it seems only appropriate that the animal making us reconsider empathy’s nature and its role in evolution is a creature so universal, and universally loathed, as the rat.

We probably won’t leave out extra trash for them—but knowing that rats may care for each other could help us appreciate them a bit more. “The basic response,” said Panksepp, “is just wonder at the marvelousness of nature.” We could even go a step further: in city landscapes and in our labs, we can try to imagine life from their perspective. We might even empathize with them.

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