Universe 25

The Mouse Utopia

The mouse utopia experiments represent a series of research studies conducted in mid-20th century America that explored the effects of population density on animal behaviour and social structures. These experiments, primarily carried out by John B. Calhoun, gained considerable public attention and were interpreted as ominous predictions for an increasingly populated world. The grim outcomes observed in the animal subjects fueled anxieties about urban overcrowding and deviant social behaviour.

The backdrop to these experiments was the rise of environmentalism and, specifically, neo-Malthusianism in the period following World War II.

Neo-Malthusians echoed the earlier concerns of Thomas Robert Malthus, who theorised that population growth would inevitably outstrip food production, leading to a struggle for subsistence. Although advancements like the Green Revolution had seemingly averted this catastrophe, neo-Malthusians remained apprehensive about the potential for overpopulation to cause societal collapse or severe adverse effects. These fears were reflected in popular writings of the time. Amidst this intellectual climate, researchers began to investigate the consequences of population growth, and John B. Calhoun emerged as a key figure in this field.

Calhoun, whose early scientific interests lay in ornithology before shifting to ethology, the study of animal behaviour, conducted his initial large-scale experiment in 1947. With the permission of a neighbour, he constructed an expansive enclosure spanning a quarter of an acre, which he named Rat City. This habitat provided ample food, water, shelter, and protection from predators, with the only limitation being the confined living space. Calhoun introduced five pregnant Norway rats to this environment, anticipating a population boom that he estimated could potentially reach 5,000 individuals. However, the population surprisingly stabilised at around 150, never exceeding 200 over the two years and four months of the experiment. Careful observation revealed a high rate of infant mortality due to inadequate maternal care, as mothers seemed to neglect their young. Additionally, the rats formed social groups concentrated in specific areas despite the overall space.

Driven by his initial findings, Calhoun joined the National Institute of Mental Health (NIMH) in 1954, where he gained the resources to conduct more controlled studies. He designed and built various enclosed habitats, sometimes referred to as "universes", to observe the behaviour of domesticated albino Norway rats under conditions of unlimited resources. After eight years of refining his methods, Calhoun published an article in Scientific American in 1962 titled "Population Density and Social Pathology". In this article, he presented the findings from six similar experiments, all exhibiting concerning trends.

These later habitats were rectangular, measuring ten feet by fourteen feet, and divided into four sections by electric fences, with three fences featuring bridges. Each section had food hoppers, water, and nesting areas accessible by spiral staircases. Calhoun introduced modifications to encourage specific behaviours, such as making the staircase to one of the centre pens shorter and varying the food supply (powdered versus hard pellets behind wire mesh) in different experiments. The experiments began with either 32 or 56 young adult rats with an even sex ratio. Calhoun estimated that these enclosures could comfortably house around 40 rats, but he allowed the populations to double before considering them almost full.

Almost immediately after the introduction of the rats, social dynamics began to break down. While females dispersed somewhat evenly, males engaged in dominance struggles, leading to a skewed distribution. Dominant males established territories in the outer pens and guarded "harems", preventing less dominant males from returning after foraging for food, which typically occurred in the central pens. This resulted in a clumping of the male population in the centre.

Calhoun observed what he termed a behavioural sink, characterised by an increase in pathological activity due to the stress of high population density. In females, this manifested as a reduced ability to build nests and care for their young, leading to high infant mortality rates, in one instance reaching 96%. Mothers would interrupt nest building, scatter their litters, and even become aggressive towards their offspring. The enclosed space also meant that females could not escape the constant advances of males, further contributing to stress.

Among the lower-class males, Calhoun identified several groups exhibiting aberrant behaviours. These included:

• Pansexuals (initially termed homosexuals), who did not compete for status and attempted to mate with any rat, regardless of gender or age.
• Somnambulists, who moved slowly and interacted minimally, appearing outwardly healthy but isolated.
• Probers, who were hyperactive, hypersexual, and pansexual, aggressively pursuing females and cannibalising abandoned young.

The conditions in these pens were described by one of Calhoun's assistants as "hell". Calhoun ended these experiments, predicting the eventual demise of the colonies due to these behavioural changes. Even when he took the healthiest males and females to breed in a less crowded environment, their behaviour was so altered that none of their offspring survived weaning.

Calhoun's 1962 article garnered significant attention, and his rat experiments were quickly linked to the perceived problems of modern city life. In an era marked by anxieties about social deviance, his findings were seen as a reflection of contemporary society and a potential future trajectory. The evocative language used by Calhoun and the design of his test environments, resembling urban settings, further fuelled these interpretations. The concept of the behavioural sinkbecame a common topic, with some psychologists drawing parallels to human behaviour in overcrowded cities, citing poor family relationships, alienation, and a lack of social involvement.

However, subsequent studies investigating human behaviour in dense urban environments yielded inconclusive results, failing to find widespread evidence of a "behavioural sink" comparable to that observed in rats. Despite this, Calhoun continued his research at NIMH, conducting even larger-scale experiments away from public scrutiny.

In 1973, Calhoun published his magnum opus, an article titled "Death Squared", in the Proceedings of the Royal Society of Medicine. In this work, he detailed his experiments with house mice in a newly designed, more vertical enclosure named Universe 25. This habitat featured 16 wall-mounted housing areas ("walk-up apartments") at the top of metal tubes, with unlimited food, water, and nesting material at the bottom. Calhoun estimated that Universe 25 could potentially hold 3840 mice, and he introduced eight mice (four male and four female) into the enclosure.

Calhoun observed four distinct phases in this experiment:

• Phase A (Social Turmoil): The initial period before the first new mice were born (lasting 104 days), characterised by the establishment of a social order.
• Phase B (Exploitation Phase): A period of rapid population growth, with the population doubling every 55 days until day 315.
• Phase C (Stagnation Phase): The rate of population doubling slowed to 145 days, and significant social abnormalities emerged. Mice unable to find a social niche withdrew, forming a large, inactive, and scarred group in the centre of the enclosure. Outcast females retreated to the highest apartments. The behavioural sink manifested again, with mice congregating at certain food hoppers while others remained untouched, indicating a prioritisation of social interaction over the need for food. Dominant males became exhausted from defending their territories, and females were forced to defend their nests, leading to aggression towards their young. Some mothers even reabsorbed unborn mice, further reducing fertility rates. Calhoun concluded that societal organisation had effectively collapsed by the end of this phase.
• Phase D (Death Phase): Characterised by a generation of young who had been rejected early and were unable to exhibit normal social behaviour. Females in this generation had fewer offspring and lacked maternal instincts. Males, dubbed "the beautiful ones", never engaged in sex or fighting, remaining physically pristine but behaviourally limited to eating, drinking, sleeping, and grooming without social interaction.

Calhoun predicted that the last mouse with reproductive instincts would die around day 1780, effectively marking the death of the colony. He concluded his article with a warning that a similar sequence of events could lead to the extinction of humankind if opportunities for role fulfillment were insufficient, leading to social disruption and individuals incapable of adapting to a complex society.

While Calhoun focused on animal populations, others applied his theories to human environments, notably prisons, which were seen as close analogues to the inescapable high-density conditions of his experiments. Studies in prisons found correlations between over-socialisation and negative outcomes such as suicide, violence, psychopathy, and stress. Environmental psychologists also differentiated between physical density (space per person) and social density (number of individuals in a space), finding the latter to be a more critical factor influencing behaviour. This research suggested that human environments could be designed to mitigate the negative effects of social density by providing opportunities for privacy.

Despite ongoing debate and criticism regarding the applicability of his findings to human societies and the potential misrepresentation of urban social problems, Calhoun's research has undeniably had a lasting influence on how America has viewed its cities and the potential consequences of overpopulation. His work continues to be cited and interpreted by various groups, reflecting the enduring and unsettling nature of the questions he raised about population density and its impact on social behaviour.