Critical Mass

Mike Freedman is an independent filmmaker based in London. He’s in the final production stages of a feature-length documentary called Critical Mass, which is about the impact of human population growth and consumption on our planet.

Mike’s staring point is the work of John B Calhoun, a US psychologist who did a lot of research into the effects of overcrowding. Calhoun’s most famous experiment is ‘Mouse Utopia’ in which he created the perfect living environment; devoid of predators, with unlimited food and water, and plenty of places for the mice to nest. The only limitation was space. Into this ‘world’ he released four breeding pairs and watched what happened. The mice took a while to get used to their new environment. In the wild, mice are located somewhere near the bottom of the food chain, so few get to enjoy a peaceful old age, making them somewhat nervous by nature. But after 104 days they started to breed.

And carried on breeding.

Over time their ‘world’ became more and more overcrowded to a point where it was impossible for them to behave like mice at all. Dominant males were unable to defend their territory and when the stress of trying to do so became too much, they simply gave up. Random acts of violence became commonplace; mothers wounded their own young and attacks on non-dominant males were not defended.  The last surviving birth was on day 600, after this point the mouse society broke down completely. Females stopped reproducing and males withdrew completely. Many of the former dominant males made their way to the most isolated parts of the enclosure. Never engaging with the other mice, eating, drinking and sleeping alone, they spent every waking moment grooming themselves, which caused Calhoun to dub them ‘The Beautiful Ones’. Despite the continued abundance of food and water, the population declined quickly towards extinction.

Calhoun’s work had a profound influence on urban planning and the design of mass transportation systems. In humans, overcrowding can lead to a decline in task performance and an increase in aggression and other anti-social behaviour. The simple fact is, we don’t like crowds. Commuters who join an already crowded train for a short journey, have much higher stress levels that those who joined the train earlier when there was more space available, even though their journeys may be much longer. There is a direct correlation between inmate density and the incidence of prison riots: overcrowded prisons are much more difficult  to control.

Overcrowding also leads to a decline in altruistic behaviour. In 1968, Bibb Latane and John Darley carried out the first in a series of studies into Bystander Apathy. The research was in direct response to the murder of a US woman called Kitty Genovase, who was killed in a brutal attack, which lasted over 30 minutes. Although the crime was was witnessed by 38 people, none of them did anything to help; no one even called the police. Latane and Darley’s experiments created similar emergency situations – researchers feigning heart attacks at a busy tube station – and their results showed that the likelihood of assistance was inversely proportional to the number of people present.  Their explanation was a diffusion of responsibility: the more witnesses there are, the less responsibility each witness feels to offer help.

Despite all the debate about climate change, population growth is the elephant in the room. Overcrowding really is going to be our biggest challenge in the short to medium term. Over the next three decades the world population will increase from its current level of 7 billion, to more than 9 billion – the equivalent of adding a city the size of Rio de Janeiro every month. Today, more than 50% of the global population live in cities – the first time in history that the proportion of urban residents has outnumbered those living in rural communities – and most of those 2 billion new people will be born in the megacities of Asia, Africa and South America (the number of megacities – those with a population greater than 10 million – will also increase from ten to 29 by 2030).


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