transcript

Speaker 1:
[00:02] It's 1958, on a farm in rural Maryland, in the USA. Inside a huge converted barn, a scientist named John B. Calhoun is perched on the perimeter wall of an enormous enclosure, teeming with rats. He's watching and taking notes.

Speaker 2:
[00:19] He cuts a hole so he can look down at this rat population. He films, he takes photographs, and he allows his population to grow.

Speaker 1:
[00:30] Calhoun knows a lot about rats, and he's calculated that there's room in these enclosures for around 50 of them to live comfortably. But there's more than that in here. He's keeping the population steady at 80, slightly too many for comfort. And he's seeing what happens.

Speaker 3:
[00:45] Calhoun started to notice a number of aberrant behaviors among the rats.

Speaker 2:
[00:50] Extreme violence, sexual deviance, the breakdown of maternal care.

Speaker 4:
[00:56] All sorts of somewhat horrifying behaviors that showed up. Horrifying, disturbing, surprising.

Speaker 2:
[01:04] It really becomes a very brutal environment.

Speaker 1:
[01:08] This bizarre experiment was to become one of the most provocative and influential experiments in modern scientific history, sending ripples into the fields of ecology, psychology, sociology, urban planning, and challenging our understanding of how to live together as human beings. But at this point, in 1958, his rats are having what can only be described as a really bad time.

Speaker 2:
[01:30] He describes this as a rat utopia, but it becomes, as he later describes, hell.

Speaker 1:
[01:40] How did you first come across Calhoun? Like, where did you first encounter his work?

Speaker 2:
[01:44] I came across his work when I was really studying for my PhD. One study kept popping up, and that was a study of rats by John B. Calhoun.

Speaker 1:
[01:55] This is Ed Ramston from Queen Mary University in London.

Speaker 2:
[01:59] Why were they continuously referring to the study of rats? So I was intrigued, and, you know, when you begin to look at the study, it is fascinating.

Speaker 1:
[02:08] John B. Calhoun, or Jack, to his friends, is born in a small town in rural Tennessee. He's a quiet, outdoorsy child. He collects bird's eggs and keeps terrapins in his backyard.

Speaker 2:
[02:19] He really is an expert bird spotter, trapper, bird bander, and it's those skills that keep getting him scholarships. He worked extremely long hours and was absolutely dedicated to improving the lives of humanity, but he was an extremely intense person.

Speaker 1:
[02:39] Calhoun's first experience with the animals which would one day make his name is in 1939. The city of Baltimore has a serious rat problem and hires this bright young ecologist with a knack for animal trapping to help them get a handle on how to exterminate them. He throws himself headlong into the rat world, and he discovers a fiercely intelligent little animal whose social relationships were much more complex than he was expecting. The project in Baltimore wraps up, but Calhoun is not done with the rat. He wants to go deeper, to find a way to observe them in a more naturalistic setting than the grotty basements of urban Baltimore. So he sets up his first big experiment.

Speaker 2:
[03:17] He asked a neighbour who owns the land if he could carry out a little experiment. And I think the neighbour, he thought it was going to be like a few hutches. He sets up a quarter-acre pen.

Speaker 1:
[03:29] This enormous enclosure is surrounded by an electric fence with a 20-foot-high observation tower for Calhoun to keep an eye, godlike, on his creation below.

Speaker 2:
[03:38] He provided them with food, with bedding. He really creates what he later describes as a sort of garden of Eden for rats or a rat utopia. So he could watch the rats, of course, nocturnal animals. He borrowed a pair of night-vision goggles, very new thing. He had extremely detailed log books.

Speaker 1:
[03:59] I mean, it's an extraordinary level of detail, isn't it? Every single rat was known and numbered. Every single fight that happened was logged. I can just imagine him spending his days in this tower with his night-vision goggles on. Quite an isolating experience, maybe, for a researcher.

Speaker 2:
[04:14] I think so, yeah.

Speaker 1:
[04:16] The understanding about population growth at the time was largely derived from the work of the 18th-century economist Thomas Malthus. His theory was that animal populations follow fairly predictable boom-and-bust cycles based on the availability of resources. Animals breed prolifically, expand exponentially until the food runs out and then a bunch of them die off and the cycle starts anew. Calhoun figures that his quarter-acre pen, with an infinite supply of food and water, could have supported a population of around 5,000 rats. But it never gets near that number. It tops out at a couple of hundred.

Speaker 2:
[04:50] This is what he's trying to understand. Why did the population not expand continuously, exponentially, as many Malthusians would have feared? It wasn't predation, wasn't weather. It clearly was something that was breaking down in their society, that restricted them from developing their numbers further.

Speaker 1:
[05:11] And so this brings us back to the barn in rural Maryland at the end of the 1950s. And the bizarre experiment which was to launch Calhoun's work into the public consciousness. The goal? To try and observe this breakdown in social order, which keeps the rat numbers at sustainable levels.

Speaker 2:
[05:27] He allows the population to grow to 80. With 80, they could have spread out at 20 per pen, which would make things a bit uncomfortable, but not ridiculously so. But this isn't what happens.

Speaker 1:
[05:40] To understand why this cosy rat utopia descends into abject violence, you've got to understand a little bit about the design of the enclosure. It's divided into four chambers, with ramps to get from one to the next. The two end chambers are quickly occupied by a dominant male and his harem of females, who live there largely in peace.

Speaker 2:
[05:59] But that means that the rest of the population, some 60 or so rats, are crowded into the other two pens. And in those spaces, the behaviour of the population really begins to break down.

Speaker 1:
[06:14] Activities, which a rat would usually do on its own, like feeding or grooming, are now inescapably social activities, and the rats become conditioned. Pretty soon, they won't eat at all unless another rat is close by.

Speaker 2:
[06:26] So he has these really striking pictures of two water droppers right next to one another. One is completely empty and the other is crowded with animals. And the animals are biting each other and they're all trying to get to the same water dropper. And because they're all together, there are continuous outbursts of violence. They're really biting deep to the point that some of the animals are killed, there's cannibalism, the mortality rate soars, and yet the animals continue to cluster together.

Speaker 1:
[06:59] Some of the males have deeply disturbed mating behavior, mounting females who aren't in heat, other males, juveniles, anything. The females have become less and less able to look after their young. They build shoddy nests or no nests at all, or abandon their pups to die on the enclosure floor. And some animals withdraw completely from this world of sex and violence, retreating to the highest nesting boxes they hide themselves away. They don't fight, never mate, don't interact with other rats at all. Poetically, Calhoun calls these ones the somnambulists, the sleepwalkers. Calhoun gives a name to this suite of weird behaviours. The violence, disordered mating and the abandonment of young. He calls it the behavioural sink.

Speaker 2:
[07:44] The behavioural sink. The behavioural sink captures an exacerbation of pathological behaviour that is the result of crowding. He wants us to have negative connotations when he describes it. When you think of the word sink, you think of moral, not just physical squalor. So you think of a pool, a pit of waste, a drain.

Speaker 1:
[08:07] Do you think, even at this early stage, he was already thinking of his work as an analogy for human societies?

Speaker 2:
[08:13] I think so. He is using language like, you know, juvenile delinquent and child abuse in the way that he describes the treatment of rats towards their pups. So it really is designed to make you think of human beings.

Speaker 1:
[08:28] The thing is, at the time Calhoun is working, overcrowding is beginning to become something of a hot-button topic. There were around 2 billion people in the world in 1930. By the late 1950s, it was approaching 3 billion, and demographers began to be nervous about what looked like an exponential upward curve. Predictions flooded in. Another billion people on earth by the mid-70s, they thought. Six, maybe seven billion by the year 2000.

Speaker 2:
[08:55] There's a fear that human beings are just going to outstrip resources. Demographers saw in Calhoun a really clear measure of psychosocial breakdown as a consequence, many thought, of crowding.

Speaker 1:
[09:09] Calhoun writes up his experiment for Scientific American, and it goes, well, in today's parlance, we'd say it goes viral. His paper becomes one of the most widely cited articles in the history of psychology. High density living is explicitly linked to high crime rates, juvenile delinquency, even admission to mental hospitals, and behavioural sink becomes a rallying cry for the moral rot at the heart of American cities. In the late 1960s, the population debate escapes from the world of academia and enters the public consciousness in a big way. One of the triggers is a book written by husband and wife team Paul and Ann Erlich. He is a Stanford professor of biology, she an ecologist at the University of Kansas. Citing Calhoun's work, they paint a picture of a catastrophic future, an overpopulated world, famine, disease, and social upheaval, and eventually, as they called it, the race to oblivion. It was called the population bomb. It sold over 2 million copies. Society in the 1960s and 70s was embroiled in a full scale population panic.

Speaker 5:
[10:15] There were quite a few books and movies and things that followed this Malthusian prediction that population was growing exponentially and it was going to outstrip food supply. And this keeps coming up over and over in science fiction.

Speaker 1:
[10:27] Melinda Mills is a professor of demography and population health at the University of Oxford.

Speaker 5:
[10:32] You know, I've always been someone that's into dystopian science fiction. And I think that's probably how I got into demography as well too. Around that time, you had Charlton Heston starring in Soylent Green. You know, we were in the year 2022. We were overpopulated, overheated, resource depleted, and humans had moved to actually eating wafers that were recycled actually from dead humans.

Speaker 1:
[10:57] Spoiler alert to people who haven't seen Soylent Green, but yes.

Speaker 5:
[10:59] Oh, sorry. Spoiler alert if you haven't seen it yet.

Speaker 1:
[11:02] How do demographers feel about population growth now? Are we still worried about it in the same way that we were in the 60s and 70s?

Speaker 5:
[11:09] Well, it's really interesting. So we get this panic, this population panic every few years for different reasons. There's this hysteria like the population bomb that come out every once in a while. But what we have now is that low fertility is going to result in us going extinct. Elon Musk tweeted a few years ago that population collapse is a risk to civilization, bigger risk than global warming.

Speaker 1:
[11:34] I mean, how bad is the problem? How worried are countries about their shrinking birth rates?

Speaker 5:
[11:39] So last year, the South Korean government declared a national emergency over low fertility rates. So in Europe, there's been recently, for example, in Hungary, they've had very low fertility. So they have a lot of pro-natalist policies from Orban's government. But generally, those haven't been working. And I mean, it's a real issue across Europe.

Speaker 1:
[11:59] According to UN predictions, growth is slowing and projected to flatten and eventually reverse later this century. But for now, it's still rising.

Speaker 5:
[12:07] There's still high population levels in sub-Saharan Africa, Nigeria, India.

Speaker 1:
[12:14] In Calhoun's experiments, he saw this idea of behavioral sink. He was concerned about the collapse of society, the eradication of all societal norms. I mean, in the human world, I suppose this would translate to high crime, for example. Is that something that demographers are worried about?

Speaker 5:
[12:28] Yeah. So Calhoun, it was interesting what he drew from his experiments. I think the sink that he talked about, it was really about context deprivation when people don't have a stimulating environment or they feel alienated in dense modern cities. So really the main mechanism there is economic. Housing is a really big issue. Employment is a big issue. So it's not population density per se. Overpopulation, it's actually about consumption. An average American consumes the same amount of energy in one month than an average Indian does in one year.

Speaker 1:
[13:05] The curious thing about the population doomism, which emerged from the work of Calhoun and others, is that Calhoun himself didn't subscribe to it at all. Ever the optimist, he believed his rat research was offering us an opportunity to rethink how we live now before it's too late. He supports projects improving the physical design of mental institutions to give patients more privacy. And he testifies in court as an expert witness in a high-profile case about overcrowding in prisons. He campaigns against the policy of slum clearances, which often displaced the inhabitants with little regard for where they end up. Meanwhile, back in the world of academia, researchers are still keen to find out whether his work on rats really translates into the human world. Among them is a social ecologist at the University of California called Dan Stokels.

Speaker 3:
[13:53] I thought the work was pretty powerful, and I began to wonder whether the kinds of negative behaviors that Calhoun observed in this rat colony would also be typical of humans living in highly dense environments.

Speaker 1:
[14:08] Today, Dan is Chancellor's Professor Emeritus at the University of California, in the School of Social Ecology. Back in the early 1960s, he was skeptical about the doom laden prophecies about high density living.

Speaker 3:
[14:19] It occurred to me also that density was often desirable. For example, people like highly dense crowded parties, or they like to go to athletic games, soccer matches, or football games, where there are a lot of people and there's a kind of excitement around that. So, I began to think about distinction between density and crowding, where density is the physical condition of a large number of people per unit space, and how that was different than the psychological sense of crowding, which I viewed as a more negative subjective state, where people felt that they didn't have enough space for what they needed to do.

Speaker 1:
[14:59] When Dan did his own lab experiments back in the late 60s, he found this distinction bore out. He got groups of students together, either packed into a small room or more spread out in a larger one, and then he made them do tasks. The size of the room didn't seem to make much difference to people's comfort levels, unless he put them in a tricky social situation. Participants who were made to compete with each other reported feeling crowded in both rooms, no matter the size. But the negative impact was magnified in the smaller room.

Speaker 3:
[15:29] When you had a more negative or taxing social situation, they were the ones expressing higher feelings of crowding and negative reactions to it.

Speaker 1:
[15:38] Right. When you say negative reactions, I mean, what are the psychological effects of crowding?

Speaker 3:
[15:43] Well, some studies have shown that when people are in highly dense situations, they feel that annoyance of subjective crowding do manifest more irritation, irritability, aggressive tendencies. But I think in terms of trying to replicate the severe effects that Calhoun found in the rats, I don't see that in the human research.

Speaker 1:
[16:04] Around this time, the Stanford psychologist Jonathan Friedman brought out an influential book called Crowding and Behavior, The Psychology of High Density Living.

Speaker 3:
[16:12] He suggested that density did not have negative effects on people, but rather it was the other kinds of negative situations, such as poverty or lack of privacy, which accounted for negative behaviors, aggression. And if you controlled for quality of housing or you gave people more privacy, these effects of density would go away.

Speaker 1:
[16:35] Avoiding the feeling of crowding used to be as simple as shutting your front door. But today, Dan says there are other ways we can end up feeling crowded out, ways that are harder for us to escape.

Speaker 3:
[16:46] People are managing an overload of digital stimulation and cyber messaging can make people feel less secure even in their immediate primary environments.

Speaker 1:
[16:55] Gosh, that's so interesting. I'd never really thought about the kind of overwhelm that you get when faced with constant 24-hour rolling news or social media could be a product of a kind of an overcrowding.

Speaker 3:
[17:05] It's kind of a vicarious crowding through their devices. There's just much more volume of information to process.

Speaker 1:
[17:14] Calhoun's own lab work isn't slowing down. By the late 60s, he's switched from rats to mice, smaller animals so he can fit more of them into his rodent universes. The most famous one is Universe 25.

Speaker 2:
[17:27] Here he's being really ambitious. I mean, in all his previous studies, he's interrupted the studies at a certain point. So he hasn't let a population run from the first seeding to their endpoint. So, this is what he does with Universe 25. It really does look like this science fiction space. I mean, it looks a bit sort of a Blade Runner kind of thing. He's got these walls. Up the sides of the pen, which are very high, are the homes. So they look like little apartment buildings from ice. And again, he calls it rodent utopia.

Speaker 1:
[18:09] As conditions get more crowded, he witnesses the emergence of a behavioral sink, the breakdown of the mouse social order. Maternal care becomes erratic. Very few pups make it to adulthood at all. But the pups that did survive in this chaotic, crowded, violent turmoil, it was these animals that Calhoun became increasingly fascinated with.

Speaker 2:
[18:29] They look like they're in really healthy condition. They've got beautiful coats. They look very well fed. But this, he argues, is because they've stopped effectively behaving as mice.

Speaker 1:
[18:40] The passive, apathetic animals that he poetically described as somnambulists in his previous paper, here get an even more fanciful name. He calls them the beautiful ones.

Speaker 2:
[18:51] They don't compete with one another for space, for territory, for females, for food. There's no fighting. There's almost complete withdrawal.

Speaker 1:
[18:59] Eventually, the birth rate in Universe 25 drops to zero. All the breeding age mice are now these beautiful, empty vessels. They eat, they sleep, and they groom. And do very little else.

Speaker 2:
[19:12] He thinks they're sort of, it's an arrested development, really. They behave as if they're still very, very young mice. They exist very comfortably, but they don't reproduce, and they will eventually just die out. The last, I think, mouse dies in December 1972. And this is actually reported in the New York Times. They have a little death notice for the last mouse.

Speaker 1:
[19:39] Who died at a mouse-equivalent age of, I think, like 108, something like that.

Speaker 2:
[19:43] 108, yeah.

Speaker 1:
[19:43] Yeah. Universe 25 made headlines again. Time Magazine came to interview Calhoun and took a now-iconic photo of him, standing proudly in the middle of his universe, little white mice running over his feet. His work is still making ripples and inspiring research to this day.

Speaker 4:
[20:02] When I read Calhoun's papers, I mean, I found them really interesting. I mean, there's no doubt that he did groundbreaking work at the time, right? Really interesting stuff. And I think the work that we did was offering a fresh perspective to thinking about the effects of density. So my name is Oliver Tseng and I'm an assistant professor in psychology at the University of California. I actually draw upon ideas from animal behavior and apply to thinking about human social behavior.

Speaker 1:
[20:29] Oliver's done his own research into the psychological effects of population density. A couple of years ago, he was investigating a concept in evolutionary ecology called life history theory.

Speaker 4:
[20:38] The very fundamental premise of life history theory is that for all organisms, time and energy is limited. Organisms need to figure out how to best survive and reproduce.

Speaker 1:
[20:50] Organisms can live life fast or slow. A fast life history looks like grow quickly, breed immediately, and have as many babies as possible. Not all of them will survive, but that's okay because you'll just have more. At the other end of the spectrum, a slow life strategy is all about investment. Grow up slowly, accruing resources along the way. Have just a few babies and invest all those resources in raising them.

Speaker 4:
[21:14] I think a nice bit of putting it is that it's a focus on quality over quantity.

Speaker 1:
[21:19] The concept of life history theory is also used to tease out the differences between individuals within a species. Some rats, for example, might live slower than others. And in the field of behavioural ecology, a more densely populated environment tends to favour a slower life strategy.

Speaker 4:
[21:35] You actually see similar patterns in lizards, in fish, right? And what my research is actually really simply trying to see if this actually would show up in humans too.

Speaker 1:
[21:44] Oliver and his team compiled data from countries all over the world and they did indeed find a correlation in humans. People living in more dense conditions do have fewer children and tend to invest more in things like education, training and building a career.

Speaker 4:
[21:59] In general, you see a pretty consistent pattern. Population density itself is still associated with a slower life history even after we take organization into account.

Speaker 1:
[22:07] But how does this actually work? Couples certainly aren't downloading demographic data about population density before they decide whether or not to have kids. So, Oliver thought, there must be something more subtle at play, something deep in our psychology that nudges us subconsciously, faster or slower.

Speaker 4:
[22:23] We were curious, like, could we actually activate this slower life history in people? Even just momentarily, with information that the environment around them is getting more crowded.

Speaker 1:
[22:34] He did two studies. In the first, participants had to read a newspaper article reporting on the problem of a growing population. In the second, they just made them sit and listen to crowd noise played in on a speaker.

Speaker 4:
[22:46] Then we had them respond to some questions that got at various aspects of their life history. Like, would they want to start a family? You know, how many children do they want to have? Stuff like that.

Speaker 1:
[22:56] They also asked them questions to see how future-oriented their thinking was.

Speaker 4:
[23:00] So, for example, like one of the questions kind of goes like, would you prefer $100 today? Or would you be willing to wait for $150 like, you know, a month from now? So if people choose the second option, they are willing to wait for the larger amount of money that shows that they are thinking about a future.

Speaker 1:
[23:16] Participants who listened to the crowd or read the article reported wanting fewer romantic partners and fewer children. And they more often opted to take the larger sum of money further down the road. Their thinking had been shifted towards investing in their future.

Speaker 4:
[23:31] I think what my research sort of suggests is that perhaps there is some sort of self-regulation psychology. In dense environments, you start seeing people having fewer and fewer kids, and then you might see density go down. Who knows? Right?

Speaker 1:
[23:44] I mean, this is quite a counter narrative to the idea of, you know, Calhoun's behavioral sink, isn't it?

Speaker 4:
[23:50] I mean, so the picture that gets painted is really quite different. It sees people as, you know, very active agents. They're focusing on building themselves, their skills and abilities and knowledge. Like some rats in Calhoun's experiments were completely healthy, but they just refused to engage in any social interaction.

Speaker 1:
[24:08] These were the passive sleepwalker rats, the somnambulists, the beautiful ones.

Speaker 4:
[24:13] Maybe some of those rats were actually trying to sort of slowing their life history, to actually build their abilities. But of course, the problem here is that in Calhoun's experiments, there wasn't a lot of maybe opportunity for the rats to build anything. And so I think there are some interesting insights to kind of like applying this life history approach thinking about the effects of density.

Speaker 1:
[24:37] Calhoun's final rodent experiments in the 1970s move away from identifying the problems of overpopulation and move instead towards solutions.

Speaker 2:
[24:46] He wants to show how you can actually solve a lot of these problems with crowding with better design.

Speaker 1:
[24:53] He creates one final universe. He's back on the rats this time. He controls where they go and who they interact with, and gives them tasks which encourage cooperation.

Speaker 2:
[25:02] So the animals would have to do certain things in order to get water together. So he's building a sense of altruism among the animals. So the idea is that if you control the space, design it better, you can actually create smaller, more resilient communities within a crowded environment. And in the end, of course, in typical Calhoun style, he declares he's created super rats. They don't suffer the same problems when it comes to higher population density. So there is much less violence. So he thinks if we can do that with rats, then these are sort of ideas that we need to think about for human beings.

Speaker 1:
[25:46] It's interesting that his work that paints a sort of catastrophic picture of a potential societal collapse is more well known and more famous than the work that proposes solutions.

Speaker 2:
[25:57] Yeah, and that always bothers him. A lot of people were using his work and saying, oh, the human race is going to be just completely destroyed. He was always chastising them, saying, you have to remain optimistic. We're an extremely adaptable species, and if we could somehow design more effectively, we could solve a lot of these problems. We needed philosophers, thinkers, policymakers, designers, architects to come together and solve the world's problems. That's what he thought anyway.