Universe 25 And Overpopulation

You probably don’t need to worry.

Anthony Chin
4 min readNov 2, 2021


One of the most interesting experiments of all time was an experiment conducted by ethologist John B. Calhoun.

Universe 25

In 1962, Calhoun constructed a utopian environment, dubbed “Universe 25". He started with four pairs of house mice, four males and four females, and observed their behavioral patterns over a period exceeding five years. It wasn’t his first incarnation of the experiment, nor the last, but the utopia going to hell after just two years made it the most intriguing experiment.

Universe 25 included an unlimited amount of food and water, and nesting materials; the mice had no predators; and the temperature was kept at 70-90 degrees. It was paradise for the mice.

The trial went through 4 phases.

Phase A was the initial period of the mice adjusting to the environment. Phase B saw exponential growth of the population. Phase C was the final period of growth of the population. And Phase D was the decline and extinction of the mouse population.

By year two, the apocalypse was upon the utopia.

Calhoun described the behaviors of the mice in the experiment.

Many [female rats] were unable to carry pregnancy to full term or to survive delivery of their litters if they did. An even greater number, after successfully giving birth, fell short in their maternal functions. Among the males the behavior disturbances ranged from sexual deviation to cannibalism and from frenetic overactivity to a pathological withdrawal from which individuals would emerge to eat, drink and move about only when other members of the community were asleep. The social organization of the animals showed equal disruption. …

The common source of these disturbances became most dramatically apparent in the populations of our first series of three experiments, in which we observed the development of what we called a behavioral sink. The animals would crowd together in greatest number in one of the four interconnecting pens in which the colony was maintained. As many as 60 of the 80 rats in each experimental population would assemble in one pen during periods of feeding. Individual rats would rarely eat except in the company of other rats. As a result extreme population densities developed in the pen adopted for eating, leaving the others with sparse populations.

… In the experiments in which the behavioral sink developed, infant mortality ran as high as 96 percent among the most disoriented groups in the population.

Calhoun dubbed the mice’s behavior as a behavioral sink which was a result from overcrowding.

The experiment introduced some fear in people since, at the time, crowded urban areas were viewed as a catalyst for the moral decay of society.

Overpopulation could certainly become a problem in the future once more resources are depleted, but perhaps we shouldn’t jump the gun just yet.

Birth rates are on the decline

In 1979, China drafted a One-child Policy which was implemented from 1980 to 2015.

The primary goal of the policy was to control the size of its rapidly growing population.

But the consequences of the policy actually resulted in decreased fertility in the population and females were more than often either aborted or given up for adoption. There were also ethical concerns as women’s rights’ were routinely violated which included forced abortions.

While there’s mixed results about what the policy did for China — the most remarkable thing that occurred was that dramatic decline in the fertility rate prior to the One-child policy.

Curbing a country’s population can mitigate problems while introducing new ones, but it ultimately might not be necessary.

For example, the American birth rate fell for the sixth consecutive year in 2020, with the lowest number of babies born since 1979, according to a new report.

The U.K. and Mexico is also experiencing declining birth rates as well.

The Covid-19 pandemic could be accelerating this trend as well.

That’s not to say we don’t have issues with supplies, but our collapse may come from a completely different scenario.

Humanity won’t meet the same fate as Universe 25

Something people tend to leave out when they bring up the experiment is the fact that not all of the mice ended up going crazy though they did die out from their refusal to mate.

Researcher, Jonathan Freedman, pointed out that the mice who controlled space led mostly normal lives. Other researchers pointed that instead of population problem, one could argue that Universe 25 had a fair distribution problem.

The “apartments” set up for the mice only had one entrance, so it was possible for the the “beautiful one’s” to have one male guarding them while the females and few males inside ate, slept, and groomed. They lost touched with social behaviors but were spared from the death and violence.

Ultimately, Calhoun would concede that one could argue that overpopulation wasn’t the de facto issue with the experiment. There’s also the fact our social dynamics aren’t the same as mice and the utopia for mice could’ve just been a stressful experience and it was actually impossible for them to survive due to the habitat still being a simulation.

Even with concerns of the human population reaching 9.7 billion by 2050 and jobs becoming outdated or replaced by machines — humanity could still endure with resource management, city planning, and technological advances.



Anthony Chin

Writer, music artist, political commentator, and amateur sports bettor from South Florida. Feel free to follow.