We have all pondered and discussed intense theories about how the world is going to end. Some believe that Earth will be hit by a magnanimous asteroid and cause mass extinction in seconds, some suggest that our role in drastic climate change is what will take humanity down, some believe one nuclear war is enough to clear out the world's population, and some simply believe that a 'zombie' apocalypse is inevitable! As thrilling as the post apocalyptic films are that portray a dramatic ending to the species extinction, how about an actual study that outlines how humans may actually go extinct?
A study undertaken from 1954 to 1972 by an American ethologist and behavioural researcher, John B. Calhoun, analyses a series of experiments that were conducted to determine the desolate long term effects of overpopulation in rodents at the National Institute of Mental Health (NIMH). This study called "Universe 25" researched behavioural patterns of rodents as a grim model for the future of the human race. Calhoun spent years perfecting his methods and repeated his experiment 25 times, therefore known as "Universe 25". He created a perfect Mouse Universe or a rat 'utopia' for the rodents : unlimited food and water, multiple levels, private nesting areas and a lush floor of shredded paper and ground corn cob. The space of Universe 25, much like a room, was about the size of a small storage unit where bright and healthy mice, hand picked from the institute's breeding stock were introduced to their Utopian world. What was a seemingly apt universe for these mice, it quickly spiralled into a congested scenario that created frenzy amongst the inhabitants resulting in disturbing pathological behaviour.
The Proceedings of the Experiment
In 1947, Calhoun constructed a quarter acre 'rat city' behind his house to keep a close eye on his charges, and filled it with breeding pairs. He initially expected to be able to house at least 5,000 rats there, but over the duration of two years that he observed the city, the population never exceeded over 150. After reaching this point, the rats became too stressed in this environment to reproduce. They began behaving strangely like rolling dirt into balls rather than digging normal tunnels. They hissed, fought and grabbed at each other. This fascinated Calhoun who wondered, if the rats had everything they needed, what was keeping them from overrunning his little city?
To further scrutinise this behaviour, Calhoun built another, slightly bigger rat metropolis, this time in a barn, with ramps connecting several different rooms. The intrigued researcher built several such rat cities, hopping between patrons that supported his research with one key question on population in mind : How many individuals could a rodent city hold without losing its collective mind?
Finally, in 1954, he gained the opportunity of working under the auspices of the National Institute of Mental Health, which provided him with whole rooms to build his 'rodentopias'. Some of these included rats, while others focused on mice instead. Like an invested rodent real estate developer, he incorporated finer facilities like climbable walls, food hoppers that could serve a minimum of two dozen inhabitants at once, and lodging he described as "one room apartments." A video recorded Calhoun enthusiastically interacting with his colour coded mice in his created mice world.
"There could be no escape from the behavioural consequences of rising population density," Calhoun wrote in an early paper as he noticed that at a certain point, each of these paradises collapsed. Even the biggest, best 'rodentopia' of all, Universe 25, built after a quarter century of research, failed to break this pattern. In his final experiment, the expanse of the universe he designed could potentially hold 3,840 mice but their population peaked at 2,200 mice and began to gradually decline from there while exhibiting differing abnormal, and often destructive behaviours. By the 600th day, the population was on its way to extinction.
What were his observations?
The result showed an increase in pathological activities due to the stress involved in high population, what Calhoun described as the 'behavioural sink'. Calhoun's work became used, rightly or wrongly, as an animal model of societal collapse under conditions of overcrowding, and his study has since become a touchstone of urban sociology and psychology in general. He strongly believed that these rodents were suitable subjects to display behavioural changes almost similar to that of humans.
Calhoun described their behaviour as, "Among the males the behaviour disturbances ranged from sexual deviation to cannibalism and from frenetic over activity 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 organisation of the animals showed equal disruption." The dominant males were observed to occasionally lash out at other members, including infants. They would often bite and wound their tails as an act of aggression. In female rats, this behavioural sink manifested a reduced capacity in nest building and young rearing causing the infant mortality rate to top by 90%, again as many females became more aggressive or would refrain from maternal duties entirely.
With each set of experiment, regardless of the scale of each one, the following events would occur in this order :-
- The inhabitant rodents mated and bred in large numbers.
- Eventually, a levelling off would occur.
- The rodents in the due course, would develop hostile and / or antisocial behaviours.
- The population would ultimately head to extinction.
The death phase of the experiments consistently consisted of two stages: the "first death" characterised by the loss of purpose in life beyond mere existential risk that included the loss of desire to mate, raise their offspring, or establish a role within society. The eventual "second death" was marked by the literal end of life and the extinction of members of the Universe 25.
In the conclusion, their findings predicted that these pathological changes would have eventually led to the death of the colonies. Even as he took the four healthiest males and females and allowed them to breed towards the end of the experiment, their behaviour had changed beyond measure, resulting in none of their infants survival.
The correlation between mouse and man :-
"This is where it gets controversial," said Dr. Edmund Ramsden of the University of Exeter and the London School of Economics, describing how other scientists tried to replicate Calhoun's results in human populations. He referred to psychologist Jonathan Freedman's experiment, where he recruited high school and university students to carry out a series of experiments that measured the effects of population density on behaviour. He measured their stress, discomfort, aggression, competitiveness, and general unpleasantness. The tide began to turn on Calhoun's utopia when Freedman declared he had found no substantial negative effects in 1975. Ramsden noted that Freedman's work suggested that density was no longer a primary explanatory variable for society's ruin. He justified saying, "Rats may suffer from crowding; human beings can cope." Calhoun's research was then seen not only as questionable, but also as dangerous.
Even as wildly controversial as his work became when first published, Calhoun's theory did raise considerable concern over the years that the social breakdown of his 'Universe 25' ultimately serves metaphorical value for the eventual path the human race was prodding along.
There are other multiple theories that suggest the world's mass extinction is not that far from sight. A Business Insider article mentions the 12 signs that we are in the middle of the sixth mass extinction - the sixth time in history of life on Earth that threatened species of global fauna have experienced major species loss. The primary reasons being exploitation at the hands of humans like slaughter of multiple animal groups for wildlife trade, deforestation and increased greenhouse gas emissions that contribute to the melting of sea ice and significant sea level rise and disintegration of once rich biodiversity. An interrupted carbon cycle due to the generous increase in population size that confers to the global climate change is instrumental in recent extinctions.
An article by The Conversation lists the few scientific predictions made by a number of known names on the various possibilities of human extinction. A prediction made all the way back in 1705 that the British scientist Edmond Halley correctly predicted the 1758 return of the comet that now bears his name. This was one of the first times numbers were successfully applied to nature to predict its long term course. By the 1830s, another comet named Biela's comet, became an object of attention when an astronomical authority, John Herschel, hypothesised that it would one day intersect with Earth. Such an encounter would "blot" us "out from the Solar System", one popular astronomy book sensationally relayed.