Calhoun’s rat experimentation began in 1958, as he converted half an acre of land into the perfect rat paradise. The location he transformed had unlimited food, water, and nesting materials, in addition to various tunnels, nesting locations, and high rise walls so that the rats could not escape. With ideal climate control and the lack of any predators threatening the population’s safety, this city seemed destined to thrive.

The experiment began with a dozen adult rats, all healthy and evenly divided in gender, being let into Rat City all at once to explore their new habitat. The space was capable of housing thousands of rats, and Calhoun fully expected the experiment to result in exponential population growth.  

However, despite all these factors that promoted an ample environment for breeding, the rat population began dying off after they reached a quota of roughly 200 members, nowhere near the multiple thousands that Calhoun predicted at the start. So this brings us to the big question, why? 

What went wrong with Rat City?

Leading up to a halt in population growth and then a great decline throughout the Rat City experiment, Calhoun noticed great pathological changes amongst the rats, having evident effects on their habitual patterns and the way they interacted with others. Their behavior became so altered they could no longer function properly. 

Due to this obliteration of basic instincts, female rats were unable to properly care for their young after they gave birth, meaning that even though the rats were still trying to reproduce, the babies would all die before ever reaching maturity. Therefore, the population was unable to grow any larger than what it was at already.

While Calhoun studied the population’s mental decline, he was able to categorize the male rats into four main labels. 

• Alpha Males– territorial, guarded and protected the females and their claimed territories from other males  

• Pansexuals– respected the alpha males and did not compete for status, made attempts to mate with any rat regardless of gender or age including babies and alpha males, the alpha males would allow these advances to happen

• Somnambulists– leisurely traveled through the pen with zero social interaction, was mutually ignored by other rats, appeared fat, sleek, and healthy because all they would do was eat and sleep and groom

• Probers– extremely hyperactive, aggressively pursued females during heat to mate with them, frequently got into fights with alpha males and were therefore covered in wounds and scars, cannibalised corpses of the young rats 

Knowing that continuing the experiment with the rats in this condition would only end in the death of them all, he chose to end the Rat City experiment here. He had theories as to why males and females lost their instincts and sanity despite living in such a perfect environment, but to support his findings first he needed to gather more data. 

In the 1950s, the experiments regarding Rat City seemed extremely relevant to current times, America struggling with the effects of The Cold War and its population on the rise. In the face of such social deviance, the public feared for society’s future after reading the fate of the rats in Calhoun’s experiment. 

“The resemblance to human behavior is frightening. In humans we see poor family relationships. The lack of caring. The complete alienation. The magnetic attraction of overcrowding. The lack of involvement which is so great it permits people to watch a long drawn out murder without so much as calling the police. Perhaps all city dwellers are inhabitants of a behavioral sink.” Carl Rogers, Psychologist 

Even with such fears of America turning into Rat City 2.0, the comparisons between human cities and rat cities gave inconclusive data and did little to prove any sort of scientific hypothesis creating a tangible correlation between the two. 

It wasn’t until the late 60s that The National Institute of Health reached out to Calhoun offering to fund him in further research, their interest peaked from his past experiments and the flurry it caused to the public. 

Mice Utopia Experiments Begin 

By 1968, Calhoun had created his magnum opus, a reinvented, upscaled version of his previous experiments, known as Mice Utopia. Switching from his usual experimentation with rats, Calhoun chose to use albino house mice, notably for their ability to prevent communicable disease. Calhoun designed a brand new enclosure for the experiment, making adjustments to several structural factors that seemed unfit in his past experiments. 

Mice Utopia’s pen, also referred to as “Universe 25,” now had lengthy metal tubes leading up to 16 different wall mounted enclosures, meant to resemble human apartments. At the bottom of each apartment there were unlimited resources once again (food, water, nesting materials, etc.), the only difference being that now there were more feeding areas to choose from than before. The experiment began with 4 healthy males and 4 healthy females, this pen holding the potential to house over 3000 mice.

The Timeline of Mice Utopia

To better understand the timeline of what happened during the Mice Utopia experiment, Calhoun organized his findings into four different subsequent phases. 

Phase A- Strive (Day 1 to 100)

During the strive period, the first 8 original mice were let into the pen. This was a crucial period of adjustment where the mice established territories and formed their nests. At this time there was a significant amount of social turmoil, as these 8 strangers struggled to claim dominance and form bonds. Once they were able to establish a social order and mate accordingly, the first litter of mice was born, leading them into Phase B. 

Phase B- Population Doubles (Day 101 to 300)

This was known as the exploit period, where the population started to double every 55 days. The first litter had all matured and had their own young now. Despite equal opportunities and the equal distribution of resources at every individual nest enclosure, more food and water was consumed in certain areas than others. Due to this phenomenon, mice began associating eating and drinking only when in the presence of others. This led to crowding in certain units of the pen while other areas remained vacant. Towards the end of this phase the population growth slowed, now only doubling every 145 days. This led into Phace C.

Phase C- Stagnation (Day 315 to 500)

This became the equilibrium period, where population did not rise nor decline. Mice lacking social niche would isolate themselves and withdraw from society. Males with no purpose would gather in the center of the pen and do nothing, growing agitated from boredom and attacking one and other. These mice had many wounds and scars, especially bitten tails, and there was nowhere to hide from the attacks so they would often endure them without fighting back. Outcasted female mice would retreat to the highest level of “apartments” and live amongst each other with little social interactions. 

During this period is when Calhoun observed the same mental decline that happened during Rat City begin in Mice Utopia. As young mice matured they started to challenge the original alpha males of society, putting the alpha males under extreme stress at such a large population, constantly forced to patrol their territory and defend it from other males. These alpha males eventually reached a point of exhaustion, unable to defend the females in their groupings anymore. 

This led to the females in the colony having to defend the nests themselves, causing them to become stressed and aggressive. This aggression would be unleashed on their newborns, who would become wounded and exiled from the nest before they were ready. The larger population meant a bigger threat, and the mother was not able to give enough attention to its young. Abusive and neglectful mothers led to a new generation of undeveloped adults.

Phase D- The Death Phase (Day 560+) 

During this phase, the newer generations really took a toll on society, these inhibited, undeveloped adults unable to exhibit normal social behaviors. At such a high population of over 2,200 mice now, the majority of the territory had already been claimed, making it difficult for young adults to find a place in society. Males seeked acceptance and would permanently withdraw after facing rejection. Instead of using the space provided, mice huddled together in small spaces, leading to prevalent violence and aggravation. Majority of the male society in this crowd was severely injured. 

Some of the newer generations, known as “The Beautiful Ones,” chose to isolate themselves from society completely. They lived in vacant areas of the pen, only existing to eat, drink, sleep, and groom. They never partook in social interactions or made attempts to mate, too undeveloped to have social implications or interact with stimuli. These mice got their nickname because of their excessive grooming and lack of any fighting scars. 

At this point the population began to decline, never surpassing the 2,200 range. Every day the mice became less aware of each other’s presence, constantly huddling closer together and lashing out violently. The colony slowly dwindled down into nothing. 

What can we learn from Mice Utopia and Rat City? 

Calhoun’s greatest findings from his experiments is a term he coined as “behavioral sink,” which describes the collapse in behavior as a result of overcrowding. 

Even though the subjects of each experiment were given plenty of space and unlimited resources, it still negatively impacted their psyche to be trapped inside the pen together. There was no way to ever escape the pen, and if they did not fit in with society or like the societal roles placed upon them, the only option was isolation or being outcasted. Females struggled through their pregnancies and infant mortality rates reached almost 100% as they lost their maternal instincts to care for young. Crowding occurred in all of the eating, drinking, and common areas, causing stress and aggravation, and eventually mice became so accustomed to this lifestyle that they could not eat or drink without others present. Males became disoriented from the constant crowding and resorted to sexual deviation, violence, and even cannibalism. 

These experiments model a typical population and its growth and consequential downfall when left unchecked, and Calhoun viewed it as a call to action for America’s society to make some serious changes in preservation of our livelihood.