Why a full building can feel so empty (Universe 25)

October 9, 2026

In 1968 John Calhoun gave four pairs of mice a paradise: food and water on tap, warm nesting space, and room, by his own count, for 3,840. The colony peaked near 2,200, stopped raising young, and died out. It still goes round as proof that crowding will end us. Tested on people, that claim did not hold up. Something smaller did show up in the studies, and it has to do with hallways.

What Calhoun recorded

Calhoun's paper, "Death Squared" (1973), describes the pen called Universe 25. The colony doubled about every 55 days, then stalled at roughly 2,200 mice, with about 20% of the nest sites still empty. After day 600 almost no pups survived to weaning, and the last conception was around day 920. When he finished editing the paper, in November 1972 on day 1588, 27 mice were left. Later accounts report the colony ending at zero.

Some males stopped fighting and courting. Calhoun called them "the beautiful ones": their days narrowed to eating, drinking, sleeping and grooming.

Why the mice stopped

Calhoun's reading was about roles, not space. With few mice dying young, the pen filled with healthy adults, yet there were, in his words, "few opportunities for fulfilling these potentialities." The Science History Institute's account adds that males who lost fights could not leave and start over elsewhere. Calhoun called the loss of the capacity for species-typical behaviour "the first death."

He then wrote that for an animal as complex as man, "there is no logical reason why a comparable sequence of events should not also lead to species extinction." That sentence is the extrapolation. It is a hypothesis, and The Scientist notes the experiment has not been replicated and that its implications for human crowding are a long way from the experimental design.

Does crowding harm people?

Freedman, Klevansky and Ehrlich (1971) ran three experiments in which groups did tasks at different densities. They found no significant effects of density on performance. Freedman and colleagues (1972) concluded that crowding does not have a generally negative effect on humans, and that what effects it has are mediated by other factors in the situation. Freedman restated the point in 1979: high density is not necessarily harmful.

That is not the whole picture. Paulus and colleagues (1977) reported that crowding in prisons can raise blood pressure, sweating, illness complaints and aggression, and that the number of people per housing unit appeared to matter more than the space per person. How many others you share with, not how tightly you are packed, is the thread to follow.

The long corridor

Valins and Baum (1973) compared two kinds of dormitory. In the corridor design, the layout, they wrote, requires residents to interact with too many others, and residents experienced stress and developed behaviour that may reduce it. The other design was the suite, where students shared a space with only a few others.

Baum, Aiello and Calesnick (1978) followed first-year students in long and short corridor dorms. According to the abstract as reported, the long-corridor residents were more competitive and busy with regaining control after one and three weeks, then by week seven they were more withdrawn and showed signs of helplessness. The abstract text came to us second-hand, so treat the wording as secondary.

The people we were built for

In 2011, Hill and colleagues examined 32 present-day foraging societies, more than 5,000 people. Most people in a residential band were not related to each other, and bands averaged about 28 adults. Humans lived as hunter-gatherers for about 95% of their history, so a group of that scale, with every face known, is the setting the social machinery was shaped in. That is context, not a measured cause.

A building with forty doors on one hall is the reverse. The headphones, the closed door, the nod and nothing more: Valins and Baum read that kind of withdrawal as a way of coping with too many others. Like the mice's quiet, it may be a response to a room with no group of your own in it. That reading goes beyond what any of these studies tested.

The wall

Baum and Davis (1980) published "Reducing the stress of high-density living: an architectural intervention." As reviews describe it, they put a wall across the middle of several long corridors, turning one long hall into two short ones, and friendship groups formed more readily. Hold this one loosely: it is one old study, the full numbers are hard to find, and we could not check the abstract directly.

What the evidence supports

Crowds alone did not hurt people in the lab. Density on its own had no general negative effect in Freedman's tests.
Too many others, too often, did. Long shared corridors and prison units produced stress and withdrawal.
A smaller group was the fix that was tried. A wall that cut the long hall in two was associated with friendships forming.
Beyond the evidence: the same few people, in the same place, every week. That is a reasonable guess from the above, and it was not tested. That fix was tried in dorms, not cities.

Sources

Calhoun (1973), Death Squared: The Explosive Growth and Demise of a Mouse Population, Proceedings of the Royal Society of Medicine. pmc · full text
Science History Institute, Death Squared. article
The Scientist, Universe 25 (1968-1973). article
Freedman, Klevansky and Ehrlich (1971), The effect of crowding on human task performance, Journal of Applied Social Psychology. crossref
Freedman et al. (1972), Crowding and human aggressiveness, Journal of Experimental Social Psychology. eric
Freedman (1979), Psychological Review. eric
Paulus et al. (1977), Effects of crowding in prisons. eric
Valins and Baum (1973), Environment and Behavior. eric
Baum, Aiello and Calesnick (1978), Crowding and personal control: social density and the development of learned helplessness, Journal of Personality and Social Psychology. eric
Hill et al. (2011), Science. ASU summary · abstract
Baum and Davis (1980), Reducing the stress of high-density living: an architectural intervention, Journal of Personality and Social Psychology. crossref

This article reports what these studies measured. It is not medical advice. If isolation or stress is weighing on you, talk to a doctor or a counsellor.

Film version, with the sources on screen: Why a Full Building Can Feel So Empty (Universe 25) (4:52).