Universe 25: how the famous experiment on overcrowding with mice was conducted

The Universe 25 project sought to see the effects of overcrowding on behavior.

Throughout history, different experiments have been conducted to study the phenomenon of overcrowding. However, Universe 25 may be the most famous of them all..

For this reason, we are going to dedicate this article to study in depth this research and all the phenomena associated with it, because its conclusions were very revealing.

What was the Universe 25 experiment?

To understand the implications of Universe 25, it is necessary to start from some premises that place us in the context of this type of research. Therefore, before going fully into the development of this experiment, let's make a small general introduction about the work of this kind.

During the middle of the 20th century, some ethologists decided to study the effects that overcrowding due to what were the effects that overcrowding due to overpopulation could have on individuals in the long term.. To this end, a series of experiments were developed in which a group of animals, generally rodents, were placed in a space with ideal conditions for their development and reproduction.

It could be said that a utopia was created for these animals, since they had all the resources they might need beforehand. In other words, a habitat had been artificially created in which the individuals would apparently have no problem to feed and reproduce in order to increase the original population. We will see later that Universe 25 was one of these scenarios.

That's where John Bumpass Calhoun, one of the foremost ethologists in population density research, came in.. This author was one of the most prolific in this type of studies. In fact, it was Calhoun who created the so-called Universe 25, among many other scenarios of rat and mouse utopias.

The starting hypothesis for this type of experiment was that the chosen site should provide accommodation and sustenance, without any problem, until the population reached a critical point, which was estimated by making a series of calculations and depended fundamentally on the area of the enclosure, always taking into account that there was enough food and water for all the individuals and that there were no external threats.

But the results were implacable: this critical point was never reached, because the population collapsed much earlier. Why?

Creation of the Universe 25

But what happened in Universe 25? Why did what was born as a utopia end up becoming more of an apocalyptic dystopia for these rodents? To find out the answer to these questions, we are going to enter fully into the development of this experiment. We will have to go back to 1968, the year in which John B. Calhoun created a new world for a small group of mice..

Universe 25 had an area of 6.5 m2, which originally housed a small population of 8 individuals. If there was a paradise on earth for mice, this was it. Enough food for everyone, fresh water, no predators lurking around... The conditions were ideal. Apparently so. According to calculations, this little world should have been able to accommodate 3500 mice. But it never reached that number.

The first eight inhabitants of Universe 25 soon mated and began to reproduce, causing an exponential growth in the number of mice. in this peculiar civilization. In little more than a year, the population had successively doubled until it reached a figure of 620 individuals, at which point this growth began to slow down.

Up to that point, the rodents' life had been practically perfect. They had everything they needed and nothing endangered their lives. But life in Universe 25 was about to stop being so bucolic, because, without knowing it, they were approaching a critical figure, not because of the scarcity of resources, but because of other factors, which had not been taken into account.

• You may be interested in "Malthusianism: what is this political and economic theory?"

The decline of the project

It was then that anomalies began to appear at the behavioral level.. The behavior of the Universe 25 mice began to be erratic. It seemed that the mice were no longer as comfortable, and although they all physically fit in the enclosure, they were beginning to feel the effects of overcrowding. They were constantly crossing each other's paths when searching for food or water, or returning to the nest.

There were no external threats, but internal ones began to be generated. The mice were getting closer and closer together and that meant territorial fights, constant moving to other areas of the Universe 25, etc. And the fundamental problem arose: many mice ceased to have a role in that small society. There were no roles for all individuals.

Because of this phenomenon, many of the rodents were apathetic, they stopped moving and interacting, because they did not have a significant role in that small world.. They were of no use. John B. Calhoun baptized this phenomenon with the term behavioral drain, or behavioral sinking.

He observed that many females in Universe 25 stopped trying to reproduce. The males, likewise, moved away from the nests and simply went to the area of the enclosure where the food was found. Neighborly conflicts were constant and it was difficult to find any mouse that did not have a wound or scar due to a territorial dispute.

Abnormal sexual behaviors were observed. There were individuals that performed these behaviors in a frenzied manner, without discrimination of sexes, and then went on to not perform any copulation at all. Intrafamilial fights appeared.. Some of the mice killed their young. Others expelled members of the nest. Even cannibalistic behavior was recorded.

It must be said that not all mice had violent behaviors. There was a group, which Calhoun christened "the handsome ones", whose behavior was limited to hygienic behaviors such as hair grooming, apart from feeding and sleeping, which is the only activity to which the behavior of all the components of the colony was reduced.

The collapse

Chaos in Universe 25 was absolute. The mice's paradise had turned into a hell.. In 1970, less than two years after the experiment began, the last litter of mice in this habitat was born, so the population stagnated and began to plummet.

Individuals had lost fertility, so at this point, society was beyond salvation. What happened from then until 1973 was the progressive and inevitable death of each and every one of the mice that made up Universe 25, extinguishing forever that attempt at utopia, but leaving very interesting questions after this event.

The population progression drew a parabola whose peak was in March 1970, at which time the trend began to be negative, until 1973, when the number of mice in the Universe 25 was at its highest point, when the number of mice in the Universe 25 was at its lowest.The population of Universe 25 finally ceased to exist in 1973. Its maximum population reached 2200 individuals. Let us recall that, ideally, it was considered that this space could have housed up to 3500 mice.

But we have already seen that, due to behavioral drainage, a factor that the researchers had not taken into account, the population collapsed long before even approaching that number.

Conclusions about the Universe 25 experiment

One of the first questions that usually arises after learning about the Universe 25 experiment is how extrapolable the processes that destroyed that small civilization are to human society itself, or at least to some of them. Logically, any conclusion in this sense must be taken with extreme caution, since both scenarios are far from being comparable.

John B. Calhoun himself tried to look for such parallels in an attempt to fit what he had discovered in his study of mice into a human society. Other authors, such as Jonathan Freedman, conducted their own research, this time with people, asking a series of students to perform different tasks in overcrowded conditions.

Freedman observed that the aggressive behaviors, as well as the stress and discomfort of the participants increased as the density of people in the same space increased. In fact, some authors pointed out that, in the Universe 25 experiment, the key did not lie in the number of individuals sharing the same area, but in the number of interactions that all these animals were forced to perform.

In any case, establishing a comparison with human beings is complicatedIn any case, establishing a comparison with human beings is complicated, since human society is substantially more complex and in no case has infinite resources to make the population grow indefinitely until it collapses due to other factors, such as behavioral drainage.

Bibliographical references:

• Calhoun, J.B. (1971). Space and the strategy of life. Behavior and environment. Springer.
• Calhoun, J.B. (1973). Death squared: the explosive growth and demise of a mouse population. Proceedings of the Royal Society of Medicine.
• Freedman, J. L. (1975). Crowding and behavior. W. H. Freedman.
• Ramsden, E., Adams, J. (2009). Escaping the laboratory: the rodent experiments of John B. Calhoun & their cultural influence. Journal of Social History.