The Rise and Fall of Society

Contents

• Introduction
• Expected Results
• Early Weeks of Mice Society
• Rapid Population Growth
• Highly Populated Society
• Last Weeks of Mice Society

Introduction

An experiment named Universe 25 was conducted in 1968 by an American ethologist, John B. Calhoun. Unlike other experiments, this one raises ethical concerns but also makes us aware of something which was never studied nor observed before. The Universe 25 experiment aimed to study the effects of overcrowding in society. However, it helped to uncover something more than that. The experiment setup was such that 25 healthy mice were placed in a laboratory environment where they could be observed. They had access to food and water in sufficient amounts. In the pictures below, you can see the environment.

These are a few pictures which might help you intuit things a little bit about the mouse environment. It was a sufficiently large place. And 25 healthy mice were kept there providing all the resources they might require. Also, there were no predators to harm the mice. However, as you might guess, the living space for the mice was constant throughout the experiment. The reason for this constraint is that in real-world scenarios, such as for human populations, the space constraint is indeed present. For example, the space constraint on Earth is the land surface area, and it is important to understand overcrowding effects. Without this constraint, overcrowding would not occur, and we would not be able to observe its effects.

Expected Results

Before any experiment, unless it's too unusual, we try to have some expectations. For this experiment, we had certain assumptions:

• A healthy mouse society would form at the beginning.
• Mice in this society would not be as strong as wild mice because they are getting ready to make everything.
• The mice population would grow.
• After overcrowding, they would control their own population due to a lack of reproductive opportunity. This balance would continue.

These were my honest assumptions and expectations about what would happen. Let's now refer back to the actual experiment. While continuing with the experiment, I want you to think more intuitively about the observations.

Early Weeks of Mice Society

As 25 mice were left in this simulated world/universe, they didn’t interact much at first because they were unfamiliar with their surroundings. However, as time passed, they began to explore and became aware of where to find food and water.

Soon, the mice started forming social structures. Some mice took on dominant roles, controlling territory and resources, while others became subordinates.

Initially, it was observed that males took on a few unique roles in society, such as:

• Defending territories
• Social Interacting (low-conflict interactions)

On the contrary, it was observed that females took on other roles, such as:

• Building nests
• Social Facilitating (being together in society)
• Taking care of offspring (newborn mice)

It was also shocking to see that males who didn’t fit in were being isolated and denied opportunities to reproduce by the females. These males became stressed and disengaged from social and territorial activities.

Similarly, females who didn’t fit into social roles were also socially rejected, and with no nests or social bonding, they faced limited protection and sometimes became victims of random aggression.

As time passed, new mating behaviors began to emerge, and the first pregnancies were observed. The second generation of the mouse population was born. This new generation learned the social roles and behaviors and continued them as they grew.

Rapid Population Growth

The newer generation of mice had sufficient food, good social connectivity, and good parental care as they grew. Soon, with more mating opportunities, the population began to rapidly increase. The population initially rose from 25 to 100 mice, and the space was still adequate for managing this increase.

However, as the population continued to grow, it began doubling every 55 days—a high growth rate. As this continued, things started getting crowded.

• The younger mice had to compete for resources to help themselves grow.
• Dominant males who defended territory now had to face new, stronger males, leading to more resistance from rival males.
• Female mice who were once nurturing their babies were now stressed as they had to share their space with more and more mice.

The population reached a point where mice were rubbing shoulders more often than earlier. The territories, which were once fixed, became dynamic due to constant defense and attacks. Territorial disputes grew, and mice that were earlier more interested in creating social bonds now had to compete for resources. Social roles became harder to maintain.

Some males began asserting increasing dominance, while others withdrew due to constant fighting over resources. Younger mice found it difficult to form social structures or integrate with the existing ones as they had to fight for nesting sites, food, and space.

Highly Populated Society

New personality types began to emerge among both males and females:

• Females: Some began to isolate themselves from the chaos, seeking shelter in elevated nesting boxes away from the crowded spaces. This led to less attention on newborns.

• Males: Some males started avoiding mating behaviors. They became physically healthy, eating, drinking, sleeping, and avoiding fights. These behaviors further broke down the social order.

As time passed, changes in behavior that had never been seen before emerged. These included:

• Increase in rape: Defined as non-consensual mating attempts. As males became more desperate for mates in the crowded, stressful environment, violent mating behaviors—including forced copulation—became frequent. Female mice were increasingly subject to these advances, and the violence escalated. This marked a significant departure from the colony's original balance, where mating had been more cooperative.

• Infanticide: As social structures disintegrated, maternal care diminished drastically. Female mice, overwhelmed by stress, abandoned or attacked their offspring. Infanticide became alarmingly frequent, leading to widespread mortality among pups. This was a stark deviation from typical nurturing instincts, highlighting the destructive impact of overcrowding and social collapse.

• Cannibalism: Despite no food shortages, cannibalistic tendencies emerged in the later stages of the experiment. Mice were observed consuming the remains of deceased individuals. This act was driven not by survival needs but by stress and psychological breakdown, demonstrating extreme behavioral shifts.

• Violence and social aggression: As space and resources became limited, physical aggression among males escalated significantly. Territorial males would attack intruders with unrelenting ferocity, often leading to severe injuries or death. Non-territorial males, unable to secure dominance, formed groups and exhibited mob-like violence, further destabilizing the community.

• Abandonment of roles: Gender roles, particularly maternal and territorial responsibilities, broke down completely. Females often abandoned nesting altogether, leaving young to die or survive in chaotic conditions. Males, previously protectors of territory and partners, exhibited erratic and desperate behaviors, abandoning their typical societal functions.

• Destruction of resources: Some mice exhibited destructive tendencies, such as tearing apart nesting materials or damaging community structures. This self-destructive behavior reflected the psychological toll of overcrowding, as individuals became increasingly detached from collective survival instincts.

• Asexuality: In some cases, social dysfunction led to asexuality—mice were no longer interested in or capable of reproduction. Both rape and asexuality became prevalent.

The population eventually peaked at about 2200 mice.

Last Weeks of Mice Society

By the last weeks of the experiment, the situation had worsened. There were very few pregnancies, and even when young mice were born, most did not survive past the weaning stage.

The isolated new male personalities discussed earlier were still capable of mating, but they were socially isolated, and no females came to them. Their reproductive potential was effectively nullified by their withdrawal from society.

The once-thriving population was now in steady decline. The birth rate dropped, and the society’s ability to replenish itself weakened. As the population fell, the remaining mice were largely either too stressed or too socially disconnected to sustain any meaningful reproduction.

As days passed, the population continued to shrink. Only a handful of mice were left. These final survivors were increasingly isolated, and their social behaviors had completely disintegrated. The few remaining females did not produce new litters, and the males, especially those with new personalities, were unable to establish meaningful mating relationships.

On May 23, 1973, the last mouse died, marking the extinction of the colony.