Rat Dystopia
So far, we have discussed the origins of multicellularity, the many paths to multicellularity, and circled back to ask the question - what is life?
This week, we’ll look at another aspect of multicellularity, one that manifests on a community level, rather than the individual level. To do this, we are going to take a closer look at a paper by John B. Calhoun called Population Density and Social Pathology.
I want to look at this paper because the experiments within - an extended trial of rodents in confined conditions - seems to offer perspective on the ways in which a multicellular animal - such as a mouse or rat - functions in the context of a greater whole. The mad-scientist experiment thought up by Calhoun allows us to take a step back and consider what one might be able to say about the human condition, and the ways that our environments affect our psychology.
Though the parallels are tantalizing, it is important to remember that we can’t draw clear parallels between humans and experiments done with rodents under even the best conditions. Mice are mice, rats are rats, humans are humans. There is also the fact that these studies were never repeated. They were enormously time-consuming, and seem like a unique result of a man who had spent his entire life working on progressively larger behavioral studies. It seems like Calhoun may have been the only person who was capable of carrying out the experiments - and the lack of reproducibility comes down to the fact that no one except for him was interested in babysitting a quarter acre of rats for nearly a year and a half.
Whatever the case, Calhoun did something extraordinary. In a large barn on his property, he built an enclosure capable of housing thousands of rats. He provided food, water, shelter, and the rats to enjoy it. After more than a year, he emerged a man certain about the fact that human society was driving people to the brink of madness.
Onwards, to Rat Utopia.
John B. Calhoun’s interest in animal behavior when Mrs. Laskey of the Tennessee Ornithological Society taught him to band birds. He published his first paper on animal behavior at the age of 15, and then continued his study of animal behavior as a student of ethology, animal behavior, at the University of Virginia. During his summers at the university, he continued his ornithology work with the Alexander Wetmore, assistant secretary of the Smithsonian Institution.
During his PhD his attention shifted closer to Earth, when he began his studies of the 24hr rhythms of the Norway rat. Whatever he found in these studies was enough to keep his attention for the rest of his life, trudging ever-deeper into the complex world of rodent social behavior. His first foray into large-scale explorations of rodent behavior took place shortly after his appointment to the Rodent Ecology Project at Johns Hopkins University in 1948.
Inspired by what he was discovering at the university, he convinced a neighbor to let him borrow a 1/4 acre plot of unused, forested land. On it, he constructed a 10,000 square foot pen that was open to the elements. He stocked it with ample food, water, and material for building shelters, and dubbed it “Rat Utopia” - the kind of place where a rat would never want for anything. He estimated that the enclosure was large enough to house 5,000 rats, but he was unsure of where the population would stabilize, or what phases it would transition through on its way there. To find out, je seeded the pen with five pregnant females and sat back.
For 28 months, he tracked the rodent populations in the pen, noting any behavioral and social changes. During the two years that he monitored his colony, he found some oddities - the number of rats in the population never exceeded 200 - despite his earlier calculations of a 5,000 rat carrying capacity. In addition to the surprisingly low population density, the distribution of the rats through the enclosure wasn’t uniform. Instead, rats would organize themselves into discrete social units with 12-13 members. He reasoned that this was the natural balance point between a functional society and psychological chaos. Any more individuals and the group would be forced to splinter into a smaller group - perhaps a reflection of the limited number of stable social connections each rat is capable of forming.
At the end of the experiment, Calhoun was interested in pushing the limits, to see what kinds of changes began to occur as he increased social density - the number of individuals in an enclosure. To this end, he secured a strain of domesticated albino Norwegian rats - the quintessential lab rats - and built an slightly more complex indoor enclosure. This version was significantly smaller than the 1/4 acre pen. It was square, partitioned into four sections, with a pane of glass across the top that allowed the researchers to look into the pen. There was also a door on the side that would allow the researcher access. No photographs of the setup are available, so we will have to rely on the illustrations Calhoun himself made for his Scientific American publication.
Drawing of Rat Utopia #1. Pens I and IV are not connected to each other, but are connected to pens II and III, respectively. Topology of the enclosure is linear, with pens II and III serving as the center.
There are four chambers, separated by an electrified fence, with a staircase connecting three of four chambers - they are the black grids that bridge compartments I & II, II & III, and III & IV. There is no staircase between chambers I and IV, effectively creating a linear flow through the habitat.
At the edges of each compartment are what amounts to housing towers, with covered nesting quarters at the top of a spiral staircase. Compartment IV shows a cutaway perspective on the tower, demonstrating the apartment-like setup of five nests on the inside. In each compartment there were food containers and water trays, offered ad libitum.
To initiate the experiment, Calhoun seeded the four compartments with an equal number of male-female pairs and waited for their populations to grow to 80 individuals. After that point, he removed any new pups that were born so the population remained stable at 80 individuals. This amounted to 20 individuals per compartment, which was a 75% increase over the preferred group size of 12 in each compartment.
After several months in the pens, he observed that the rats would cluster into a few distinct types of groups - small, medium, and large. The medium groups had equal numbers of male and female rats, but he reliably observed that small groups tend to skew female, while larger groups skewed male. The small groups - i.e. many females to a few males - were found predominantly in the end pens, I and IV, while the larger groups were found predominantly in the center pens, II and III. This meant that the male population was predominantly relegated to those two pens. Overall, the center pens had a much larger population that the end pens.
The mechanism by which this gender and population segregation occurred was aided by a synergy between Calhoun’s design and the process by which the rats oriented themselves in the social hierarchy. Young male rats undergo a period of aggressive status determination, during which they fight for dominance. During this period of fighting, many young rats would awaken early to forage for food before the rest of the colony was active - effectively avoiding the incessant fighting while getting read for the day.
This early rising behavior prevented fights, but paradoxically led to an increased density of males in the two middle compartments. This was likely due to two factors - food and access. Calhoun had developed a special feeding trough, where kibble was hidden behind a wire mesh, that required animals to spend much more time and effort during feeding. Since pens II and III were accessed from two sides, they quickly accumulated a larger population, where this sort of behavior seemed to amplify itself to the degree that Calhoun reported he rarely, if ever, saw animals eating by themselves.
So when male rats in pens I and IV woke up early to go get food, they would go to the main watering holes - pens II and III - to get it. But the dominant males in pen I and IV had set up their living quarters at the bottom of the single ramp that led to those compartments. When these early risers attempted to return, these dominant males would wake and drive them back into the central pen - effectively causing the population density of the central pens to increase, while the peripheral pens lived quite comfortably.
This spontaneous increase in population densities in the central pens of the experiment created what Calhoun referred to as a “behavioral sink,” a situation that far surpassed the population densities the wild rats in the first experiment appeared to prefer. This sort of density resulted in severe disruption of normal rhythms, which Calhoun found to be most apparent in the nesting behavior of the females.
“Rooms” are replicates of an entire 16 month experiment, and pens correspond to roman numerals I-IV. The increases in eating took place in one of the central pens each time a specific kind of food hopper was used. In all three cases, population of the central pens is much greater than the edge pens - though this relative concentration is not the same in all trials. Black and hatched bars represent male female ratios, which are not as robust across populations - or as simple as the story reported by Calhoun in his Scientific American piece.
In the brood pens, the low population I and IV pens, where there was a high female:male ratio, Calhoun measured a 50% survival rate of newborn pups. This seems low, but rats have large litters, up to 15 pups at a time, because in the wild there is some significant percentage that does not survive to adulthood. However, in the females that were in the high-density feeding pens, II and III, between 85 and 90% of the pups died before weaning.
Calhoun attributed this lower likelihood of survival to the overabundance of males that would relentlessly pursue females, whether or not they were willing to mate. This meant that pregnant females, normally free to occupy themselves with the tasks of nestbuilding, were constantly being interrupted by males looking to copulate. This effectively short-circuited the female nesting behavior and although they were pregnant more frequently, they were much worse at taking care of their litters.
The behavioral sink had long-term negative effects for females, who died at a much higher rate than the male rats. By the end of 16 months, a quarter of the females had died from complications with pregnancy or birth - while only 15% of males had died from any cause.
That is not to say, however, that the males didn’t suffer any negative consequences.
Some males managed to avoid the worst of it, and were permitted to remain in these peripheral pens - but in return, these “phlegmatic males” had to accept the dominance of the sentinel without argument. They would spend most of their time burrowed with the females, rarely engaging in sexual behavior of any kind. They would emerge to eat and sleep, and then return to their sleeping quarters until they were stirred by physiological need.
The dominant males that managed to secure brood territories were largely exempt from complication - but in the densely populated middle pens, the fight for dominance never ceased. Periods of relative peace would be interrupted “at regular intervals during the course of their waking hours, [when] the top-ranking males engaged in free-for-alls that culminated in the transfer of dominance from one male to another.” Even those males that succeeded in making it to the top of the hierarchy would periodically go berserk, “attacking females, juveniles and the less active males, and showing a particular predilection -which rats do not normally display - for biting other animals on the tail.”
Those males that did manage to rise to the top of the dominance hierarchy displayed other, abnormal behaviors. There were the pansexuals, who would engage in sexual activity with anyone - male, female, juvenile - that would tolerate their advances. The “somnambulist” rats were the ones that “ignored all the other rats of both sexes, and all the other rats ignored them.” The “probers” were the final group of males that emerged in the densely populated central pens.
They were hyperactive, constantly searching for sexual partners. But their coitus was disturbed, as they would submit to vicious attacks from the dominant rats without defending themselves, and would return, over and over again, to their position at the top of the ladders that led to the brooding pens. There they would wait for passing females with whom they could engage in coitus. These probers were incapable of performing ritual mating practices and would follow females into their burrows to mate - where they would often cannibalize the pups that they found.
At the end of the 16 months, Calhoun selected four of the healthiest males and females and moved them into new living conditions - free from the disquieting density of the interconnected pens. They were six months old, in the prime of their rat lives - but he found that they did not recover normal function. The females gave birth to fewer litters than was expected - and none of the young that were born survived to maturity.
Rats all, folks.
In all, Calhoun repeated the experiment three times and observed similar results with each repetition. In a second round of experiments, he made some modifications to the food hoppers that produced the behavioral sink and found slightly different outcomes. When provided with powdered food rather than the pellets hidden behind a metal mesh, much of the aggregation behaviors around the food disappeared.
The second round of experiments, without the markings of a behavioral sink. The distribution of males and females is much more distinct in this population - with a greater number of females overall, and a greater disparity visible between sex parity in the different pens. Low numbers of males represents a “territory,” controlled by a single dominant male that drives the other males into neighboring pens.
In this second round, it was water that was difficult to get - not food. But for whatever reason - perhaps the lack of dopaminergic effects of drinking water there was less conditioned clustering. The lack of behavioral sinks in the second round of experiments resulted in a much less marked distribution of males and females across the different pens of the experiment - but the behavioral oddities caused by high density remained.
The wire-mesh food hopper used in the experiments that displayed the development of a behavioral sink. Habituation to feeding together at a specific hopper caused a conditioned desire to eat at the same location, in the presence of other rats.
Powder feeder used in the second round of experiments, where rats did not have to spend a significant amount of time acquiring food. The lack of social conditioning prevented the formation of a runaway behavioral sink.
In the years since this study, many have wrestled with what truths might be hidden between the rodent lines. Fears of urban environments affecting normal sexual development, leading to the breakdown of society because of women no longer interested in childrearing, a breakdown of sexual mores, and an acceptance of progressively non-normative sexual behaviors that include asexuality.
Calhoun himself was certain that this was a version of our own society, which would be driven to the brink by overpopulation and overcrowding. But despite numerous attempts in the years following, few researchers were able to find evidence of a behavioral sink - a self-perpetuating behavior that prevented normal functioning - in human societies.
However, it’s possible that researchers didn’t look closely enough to properly interpret urban conditions, or that the definition of a behavioral sink is too simple. It’s also possible that the intervening decades, with an increased push towards LGBTQ acceptance and an increase women’s liberation, have made it difficult to examine Calhoun’s conclusions without threatening the identity of precarious social groups.
It may be, however, that cities themselves are behavior sinks, rather than there being specific aspects of city life that represent the behavior sink. In this case, the jobs, restaurants, shopping, and nightlife would be the activities that cause us to cluster in social densities far above our preferred group sizes. In turn, the increased density of these activities would be causing the emergence of various personality disorders and mental instability that plagues millenial youth.
When Calhoun was doing these experiments, there were two things that must have caused him great worry - that the population had increased every year for as long as could be measured - and that people were streaming into the cities, more and more every year. But with the invention of the internet, tons of work-from-home options, the dispersal of the internet into all corners of the Earth, it seems that we might be coming into a future that Calhoun couldn’t have imagined. In this version of the world, we are able to spread out in such a way that we aren’t forced into close contact with people that we are constantly jostling with for dominance.
The next few decades of social shifts will be instrumental in understanding how urban living environments affect social structures. If de-urbanization proceeds as quickly as some are hoping, we should be able to evaluate the accuracy of Calhoun’s conclusions within a generation or two.
