Are people just rats after all?

Back in the 60s and early 70s I remember reading a story in Scientific American about a psychologist (John B. Calhoun) who performed an experiment with lab rats (an experiment that probably would not be permitted these days). He built them a large, comfortable habitat, and gave them all the food and water the wanted. He kept their habitat well cleaned, with fresh litter every day. Beyond that, he did nothing. He let them breed without limits. As more rats were born he provided more food and water and clean litter, but not more space. Their living space was kept constant.

As the population grew the rats started getting more short tempered and more "neurotic". Attacks on each other increased, and rat suicides became a frequent event. Before long the habitat, in spite of being well stocked and routinely cleaned, descended into chaos with violence, paranoia, and a complete breakdown of the normal social structure of a rodent colony.

To quote Calhoun himself:

Many [female rats] were unable to carry pregnancy to full term or to survive delivery of their litters if they did. An even greater number, after successfully giving birth, fell short in their maternal functions. Among the males the behavior disturbances ranged from sexual deviation to cannibalism and from frenetic overactivity to a pathological withdrawal from which individuals would emerge to eat, drink and move about only when other members of the community were asleep. The social organization of the animals showed equal disruption. ...

... infant mortality ran as high as 96 percent among the most disoriented groups in the population.

Quoting Wikipedia re his final experiment:

... the rats were said to be in "rat utopia" or "mouse paradise", another psychologist explained....

Following his earlier experiments with rats, in 1972 Calhoun would later create his "Mortality-Inhibiting Environment for Mice": a 101-inch square cage for mice with food and water replenished to support any increase in population, which took his experimental approach to its limits. In his most famous experiment in the series, "Universe 25", population peaked at 2,200 mice and thereafter exhibited a variety of abnormal, often destructive behaviors. By the 600th day, the population was on its way to extinction.

Lewis Mumford writing in his book The City in History noted:

No small part of this ugly barbarization has been due to sheer physical congestion: a diagnosis now partly confirmed with scientific experiments with rats – for when they are placed in equally congested quarters, they exhibit the same symptoms of stress, alienation, hostility, sexual perversion, parental incompetence, and rabid violence that we now find in the Megalopolis.

We wonder why our world seems to be going crazy? Could it be as simple as too many people, too much crowding, too little personal space? Are we just like those rodents in that respect?