Of Mice and Rats

Rodent lessons on overpopulation, "behavioural sink," and social disintegration

Jon Mills

Photo (CC BY-SA 3.0), Polarqueen via Wikimedia Commons (cropped from original)

In the 1940s, ethologist John Calhoun began to study the effects of population density on rats. He confined wild Norway rats to a quarter-acre enclosure where they had a bounty of food, plenty of space to mill about, removed any source of predation or conditions for disease, and he watched.1

Soon a colony formed and the population boomed. But by the end of 27 months, the population stabilized at only 150 adults, despite the fact that reproduction rates were predicted to produce 5000 by that time. One reason was an extremely high infant mortality rate. Despite an adequate amount of space, stress from social interaction led to disruptions in maternal functions where very few young survived.

This observation in the wild led to a series of more controlled experiments using domesticated rats indoors. As the population density increased, behavioural pathology emerged among both females and males. Females were largely unable to carry a pregnancy to full term, died after delivery if they did, or neglected their litters if they survived. Males became more frenzied, aggressive, resorted to sexual deviation, even cannibalism, followed by morbid withdrawal, where they would only come out to feed or roam about when others in the community were asleep.

Social disintegration soon occurred: factions of rats divided into different groups with modified sex ratios, congregated in certain pens while leaving other areas sparse, ate rarely or only in the company of other members, and eventually crowded together in a pen as one big mob. This aberrant social phenomenon, a “pathological togetherness,” disrupted courting practices, building of nests, and nursing and caring for the young. Infant mortality rates ran as high as 96% for the most disordered groups in the colony.

With this background in mind, Calhoun set out to create the perfect world, this time with mice.2 He constructed Utopia: Universe 1. The basic design consisted of a closed physical universe approximately 9 feet square and 4.5 feet high with galvanized metal walls at the top. There were tunnels and layers comprised of segmented units and segregated cells with separate story apartments, retreat nesting boxes, food hoppers, water dispensers, and an open congregation floor area covered with ground corn cob to allow for communal feeding, social interaction, and access to each tunnel.

As the population expanded, young males grew into adult male counterparts competing for roles in an already established social order. With no place to emigrate, those who failed withdrew “physically and psychologically,” became despondent and inactive, and pooled on the floor near the center of the universe.

The mice had everything they could ever dream of: unlimited food and water, shelter from the elements, disease, predation, and invasion from other species, and an ambient temperature. The initial four pairs of mice doubled rapidly until reaching a population of approximately 620, before the exponential growth started to slow as a new social organization arose.

All was good in paradise until males began to compete for dominance and hierarchy in this closed social system. The most successful males were associated with brood groups that produced the most litters, but as the population expanded, young males grew into adult male counterparts competing for roles in an already established social order. With no place to emigrate, those who failed withdrew “physically and psychologically,” became despondent and inactive, and pooled on the floor near the center of the universe.

As the senior territorial males became more fatigued in fending off their maturing associates, they were also less successful in defending their territories, which left nursing females more exposed to invasion of their nests. As their nest sites became more vulnerable, females adopted the aggressive role of territorial males, which included attacks on their own young who were maimed and forced to leave the nests before normal weaning. Soon conception declined, pregnancies were aborted, offspring were wounded during delivery, and mothers carried their young outside of the nest to abandon them.

The social matrix began to collapse when females rejected their progeny, and pushed them out into the dense and dangerous jungle before the development of any attachment or affectional bonds were achieved.

Successive generations were increasingly unable to engage in species-normative behaviors including: courtship, procreation, maternal care, territorial defense, and hierarchical intra- and intergroup organizational complexities, to the eventual point of extinction. The last surviving births were on day 600 after colonization. Conclusion: when the spirit dies, the species dies.

Calhoun pointed to the “behavioural sink,” the tendency of disenfranchised groups to become fragmented in their behaviours to the point of societal decay due to the accumulation of negative interactions with others, absence of defined roles, and overpopulation.

What we may garner from Calhoun’s experiments with rodents is remarkably analogous to the human animal. When children are neglected and forsaken by their mothers and fathers, abandoned on the streets, abused by their elders and society, and subjected to insecurity and ferocity, they become traumatized, feel unsafe and persecuted, cease to function adaptively, experience ongoing stress and deterioration in health, wellness, and social adjustment, aggress on others, become hopeless and depressed, and/or withdraw to an autistic state of simple instinctual behaviours aimed at physiological survival until death.

For an animal so complex as homo sapiens, there is no logical reason why a comparable sequence of events should not also lead to species extinction. Just as biological generativity in the mouse involves this species’ most complex behaviours, so does ideational generativity for humans. Loss of these respective complex behaviours means death of the species.

In other words, if people do not have the opportunities to fulfill their aspirations, ideals, and shared communal needs, where enjoyment, purpose, creativity, and mutuality give meaning and provide a social link to life, pathology and mayhem will ensue. Calhoun called this the “behavioural sink,” the tendency of disenfranchised groups to become fragmented in their behaviours to the point of societal decay due to the accumulation of negative interactions with others, absence of defined roles, and overpopulation.

Despite the fact that it is reductive to equate the intelligence and complexity of human life to that of a mouse, it nevertheless remains a chilling reminder of what overcrowded conditions can potentially lead to in a controlled society where plenty of food and water remain available. Our current total world population is nearly eight billion, and the United Nations estimates it will likely be over 11.2 billion by 2100.

 

 

Jon Mills is a philosopher, psychoanalyst and psychologist living and practicing in the Greater Toronto Area.


This article appears in our Summer 2020 issue.

 

 

 

 

 

 

 

  1. https://en.wikipedia.org/wiki/John_B._Calhoun#Early_rat_studies
  2. Calhoun (1973) Death Squared: The Explosive Growth and Demise of a Mouse Population, Proceedings of the Royal Society of Medicine, 66: 80–88.

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