This Crazy Experiment On Mice Ended In A Dystopian Nightmare

As a species, we have tried to learn what makes people tick. Because everybody is different this has given rise to behaviour studies. Some of these are fairly ethical, some of them are less so. Some of them got weird in a hurry.

Animal experiment

One such experiment wasn’t conducted on humans at all but on the humble mouse. This might not seem like a particularly bad thing but scientist John Calhoun conducted an experiment where he created a utopia for mice. He referred to it as universe 25 as it was the 25th environment of its type he has tested.

Universe 25

The area was designed to cater to the mice’s every need. Their home contained more than enough food, water bedding and initially all the space that the furry little fellas could have hoped for. It was designed for comfort and for the mice to thrive. It contained 256 nesting boxes capable of housing fifteen mice comfortably. This meant that in total the “universe” could sustain 3840 mice.

Adam and Eve

Of course, Calhoun had to begin his experiment and he did so with 4 cherry-picked breeding pairs of mice from the national institute of health’s breeding colony. They were tested to make sure they were as healthy as possible.

The other universes

Calhoun had conducted previous experiments of a similar type. One such experiment had an enclosure designed for 5000 rats. The population never grew beyond 200 despite the fact the set up had unlimited food and water and a complete absence of predators. The populations in his experiments always stalled or the animals turned on themselves.

Calhoun had noted the tendency of the animals to crowd together. He referred to this as a behavioural sink and it was a big reason that his experiments never seemed to end with a large population. The tendency for groups to crowd together led to the breakdown of social structures. The relevance to the human population seems a bit iffy, given how much more complex human behaviours are. Some of us are introverted and prefer sparsely populated areas, whereas some of us prefer the hustle and bustle of city life.

The experiment was constructed with the explicit goal to see if a perfect society could indeed flourish. Of course, this utopia would end up becoming a dystopia.

Initial harmony

The 8 super healthy mice got off to an impressive start and after a year the population had grown to an impressive 600 rodents. Their world was relatively trouble free at this point and it seemed like maybe Calhoun had created the utopia he was hoping for. However, that doesn’t tell the full story. 35 days later there was a drop in population growth.

Social breakdown

After the first year behaviours started to become a little odd. Without any predators to fend off and without any need to compete for food sources, male rats started forming “gangs” and would randomly attack other groups of mice. Females stopped caring for their young and sometimes even attacked them and their breeding pretty much stopped. This led to male mice attempting sex with pretty much any mice (male or female) that were nearby. Also, mice would crowd together in groups as high as fifty in areas designed for 15. This was despite there being empty shelters with fresh bedding just inches away

The beautiful ones

A bunch of mice took themselves away from the overcrowding to the uppermost quarters and spent almost all their time eating grooming. These were dubbed the “beautiful ones”


Without breeding going on the population dwindled but even when it dropped to a point where breeding was rampant before, this new generation refused to breed, eventually dying out before two years had passed.


Although you have to think that this wouldn’t be what happened to humans in this scenario it is still an intriguing experiment and makes you think about overcrowding in humans.

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