Arch. Myriam B. Mahiques Curriculum Vitae

Sunday, October 11, 2009

Overpopulation in cities: John Calhoun´s experiment with rats

That´s terrible overcrowding in India.

Asian overcrowding.

Overpopulation is a term that refers to conditions by which the population density enlarges to a limit that provokes the environment deterioration, a remarkable decline in the quality of life or a population collapse. (Nasif Nahle, 2003). It has a detrimental effect on people; it is the cause of the destruction of natural habitats of many animal and vegetal; people die more and more from illnesses associated to organic and inorganic wastes; water, will be desperately needed….
Some social and psychological consequences are: tendency to dominate spaces; violence; depression, anxiety, emotional stress, quarrels in families and among neighbors; early marriage and divorce; incest, school drop outs.
Many years ago, I have seen an impressive documentary film about rats and overcrowding in comparison with humans –laboratory animals are a good substitute for humans in hazardous environments-; the documentary was based in the ecologist John B. Calhoun´s experiment with Norway rats. And, to my surprise, I found its complete explanation in Edward T. Hall´s book ¨The Hidden Dimension¨. This is the experiment, and conclusions for urban overpopulation are obvious.

A funny (?) overcrowding cartoon.

The research began at Johns Hopkins in 1946 and continued through the '60s, when Calhoun, then a research psychologist, initiated his studies of population dynamics under natural conditions, in a disused land in Towson, Maryland, by introducing five pregnant Norway rats in a quarter acre outdoor enclosure with plenty of food and no predation issues. He observed them for 28 months. The population expanded to conform a ¨rat city¨, it never exceeded 200 individuals and at last stabilized at 150, as social fights were so disruptive to normal maternal care, that only a few of the young survived. The point is that female rats, in a natural environment could have produced 50000 progeny in 28 months, but available space could not have accommodated this number.

Calhoun´s behavioural sink, 1970.

These animals grew up in confinement, for generations, without the ability of escape or migrate to a frontier. They developed social pathologies similar to humans in overcrowded cities or settlements (let us think about slums). Behavioral disturbances reached the levels of deadly fights, sexual deviation and cannibalism.
In response to invasion and the large number of males, females became aggressive and this attitude generalized to their baby rats. And so became the beginning of mortality. Overcrowding produced dramatic results ranging from aggression to many forms of abnormal behaviour, to mass die off.
Calhoun's goals are unusual because psychologists conducting this type of research, mostly apply to individuals and not social groups. Calhoun´s work remains unfinished; they should continue to produce new insights. His experiments could include a frontier or many frontiers, as this is the case of refugees and immigrants in real life.
All this text is based on chapter III of The Hidden Dimension by Edward T. Hall, including some sentences.

Further reading:
Winn, Larry. Universe 25. September 1998
Nahle, Nasif. Overpopulation. Published on 10 November 2003 by Biology Cabinet Organization.

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