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The Behavioral Sink – The Effects Of Over-Crowding On Mice

Every aspect of Universe 25—as this particular model was called—was pitched to cater for the well-being of its rodent residents and increase their lifespan. The Universe took the form of a tank, 101 inches square, enclosed by walls 54 inches high. The first 37 inches of wall was structured so the mice could climb up, but they were prevented from escaping by 17 inches of bare wall above. Each wall had sixteen vertical mesh tunnels—call them stairwells—soldered to it. Four horizontal corridors opened off each stairwell, each leading to four nesting boxes. That means 256 boxes in total, each capable of housing fifteen mice. There was abundant clean food, water, and nesting material. The Universe was cleaned every four to eight weeks. There were no predators, the temperature was kept at a steady 68°F, and the mice were a disease-free elite selected from the National Institutes of Health’s breeding colony. Heaven.

Four breeding pairs of mice were moved in on day one. After 104 days of upheaval as they familiarized themselves with their new world, they started to reproduce. In their fully catered paradise, the population increased exponentially, doubling every fifty-five days. Those were the good times, as the mice feasted on the fruited plain. To its members, the mouse civilization of Universe 25 must have seemed prosperous indeed. But its downfall was already certain—not just stagnation, but total and inevitable destruction.

But Calhoun’s work was different. Vogt, Ehrlich, and the others were neo-Malthusians, arguing that population growth would cause our demise by exhausting our natural resources, leading to starvation and conflict. But there was no scarcity of food and water in Calhoun’s universe. The only thing that was in short supply was space. This was, after all, “heaven”—a title Calhoun deliberately used with pitch-black irony. The point was that crowding itself could destroy a society before famine even got a chance. In Calhoun’s heaven, hell was other mice.

So what exactly happened in Universe 25? Past day 315, population growth slowed. More than six hundred mice now lived in Universe 25, constantly rubbing shoulders on their way up and down the stairwells to eat, drink, and sleep. Mice found themselves born into a world that was more crowded every day, and there were far more mice than meaningful social roles. With more and more peers to defend against, males found it difficult and stressful to defend their territory, so they abandoned the activity. Normal social discourse within the mouse community broke down, and with it the ability of mice to form social bonds. The failures and dropouts congregated in large groups in the middle of the enclosure, their listless withdrawal occasionally interrupted by spasms and waves of pointless violence. The victims of these random attacks became attackers. Left on their own in nests subject to invasion, nursing females attacked their own young. Procreation slumped, infant abandonment and mortality soared. Lone females retreated to isolated nesting boxes on penthouse levels. Other males, a group Calhoun termed “the beautiful ones,” never sought sex and never fought—they just ate, slept, and groomed, wrapped in narcissistic introspection. Elsewhere, cannibalism, pansexualism, and violence became endemic. Mouse society had collapsed.

On day 560, a little more than eighteen months into the experiment, the population peaked at 2,200 mice and its growth ceased. A few mice survived past weaning until day six hundred, after which there were few pregnancies and no surviving young. As the population had ceased to regenerate itself, its path to extinction was clear. There would be no recovery, not even after numbers had dwindled back to those of the heady early days of the Universe. The mice had lost the capacity to rebuild their numbers—many of the mice that could still conceive, such as the “beautiful ones” and their secluded singleton female counterparts, had lost the social ability to do so. In a way, the creatures had ceased to be mice long before their death—a “first death,” as Calhoun put it, ruining their spirit and their society as thoroughly as the later “second death” of the physical body.

Calhoun had built his career on this basic experiment and its consistent results ever since erecting his first “rat city” on a quarter-acre of land adjacent to his home in Towson, Maryland, in 1947.

But in fact the full span of Calhoun’s research had a more positive slant. The misery of the rodent universes was not uniform—it had contours, and some did better than others. Calhoun consistently found that those animals better able to handle high numbers of social interactions fared comparatively well. “High social velocity” mice were the winners in hell. As for the losers, Calhoun found they sometimes became more creative, exhibiting an un-mouse-like drive to innovate. They were forced to, in order to survive.

Later in his career, Calhoun worked to build universes that maximized this kind of creativity and minimized the ill effects of overcrowding. He disagreed with Ehrlich and Vogt that restrictions on reproduction were the only possible response to overpopulation. Man, he argued, was a positive animal, and creativity and design could solve our problems. He advocated overcoming the limitations of the planet, and as part of a multidisciplinary group called the Space Cadets promoted the colonization of space. It was a source of lasting dismay to Calhoun that his research primarily served as encouragement to pessimists and reactionaries, rather than stimulating the kind of hopeful approach to mankind’s problems that he preferred. More cheerfully, however, the one work of fiction that stems directly from Calhoun’s work, rather than the stew of gloom that it was stirred into, is optimistic, and expands imaginatively on his attempts to spur creative thought in rodents. This is Robert C. O’Brien’s book for children, Mrs. Frisby and the Rats of NIMH, about a colony of super-intelligent and self-reliant rats that have escaped from the National Institute of Mental Health.

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One response to “The Behavioral Sink – The Effects Of Over-Crowding On Mice

  1. Pingback: Daily Linkage – July 25, 2012 | The Second Estate

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