Where there are more people, there will be more crime. This isn’t necessarily the case per capita; that depends significantly on context. In the United States, there tends to be more violent crime per capita in cities than in rural areas, but there are regional exceptions and that trend is not always followed internationally. So, what can we learn, forensically, about the effects of crowding on violent or otherwise undesirable behavior?
Although it’s very dangerous to draw firm conclusions about humans from studies of infrahuman animals, it might be worth looking, at least from a heuristic standpoint, at what we know about other kinds of mammals when you crowd them together.
Nearly a century ago, Sir Solly Zuckerman examined the behavior of Hamadryas baboons, crowded together in an exhibit colony at London Zoo. The conditions were hardly natural; the baboons, of course, couldn’t get out, and the male-to-female ratio was over fifteen to one. These facts have been used to demonstrate the limitations of this early research; but the fact remains that under these crowded and unnatural conditions, the baboons beat the living hell out of each other, with a tremendous casualty rate that has never been seen for baboons in the wild. Zuckerman’s findings, sadly, were extended far beyond their actual scope; the unnaturally crowded conditions definitely influenced the results (Jolly, 1972).
But at that point, the forensic psychologist, frequently not the least cynical of scholars, might ask how “natural” are conditions in modern Manhattan, or Fresno, or suburbs anywhere?
The answer, of course, would depend on whom you ask; but studies of other mammals, under crowded conditions, reveal similar trends.
Mice and rats have been extensively studied in this regard. Granted, rodents are very different from humans, cognitively and in many other ways. Yet at the same time, like ourselves, rodents are mammals, and we share a mammalian ancestry with them many millions of years older than the advent of the first dinosaurs. Therefore, it might make sense to pay some attention to them.
And when you crowd them together, all hell breaks loose.
Studies of rodent overcrowding have been conducted by many scholars, and not all of them agree. Moreover, all can be criticized on many fronts. But some of the most interesting, from the potential standpoint of the development of new, modern research, were conducted by John C. Calhoun (1962, 1973).
When studied separately in overpopulated environments, the “social organization” of both mice and rats broke down. With overcrowding, there were far more aggressive and hostile interactions. Courtship approaches completely failed in males, or males withdrew from the mating/reproductive situation altogether.
Females showed progressive disruption of nest building. Young animals were neglected or attacked, to the degree that infant mortality reached 80 to 96%. The young were ignored, violently abused, or killed.
Oddly, in research which admittedly has not been replicated in the natural world, a group of male mice emerged that Calhoun called the “beautiful ones.” These animals withdrew completely from all interactions, from courtship and fighting, and spent all their time in what we might call hedonistic pursuits; eating, drinking, sleeping, and grooming themselves. Thus, they stayed in excellent physical shape by withdrawing completely from normal mouse society.
All of this research has been hugely criticized. The research conditions were artificial; sanitation was poor; the research was observational and descriptive, rather than conforming to the hard experimental standards preferred by nasty experimental psychologists such as myself; and some of what happened in these studies has not been replicated in the real world, including the “beautiful ones” effect. Other admittedly hypothetical sources of criticism have also been adduced.
Human beings of course possess vastly greater levels of cognition than do rodents; this has been suggested as a buffer against the negative effects of overpopulation. However, this might be a two-edged sword; our cognitive powers might also allow us to exaggerate or to minimize, in our minds, our perceptions of overpopulation. This is an issue requiring research.
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Yet if these rodent results do have any relevance for the human condition, we might expect the following from unnaturally overcrowded humans:
- Increasingly aggressive interactions, in the streets and on the internet.
- A reduction in healthy sexuality, including an increased self-isolation of many males, who might become increasingly interested in self-care and scornful of women and society at large. Such a “beautiful ones” effect, if it existed, might be expected in the modern world to spread through social media.
- The abuse, neglect, or even murder of offspring, infants and children, with a corresponding lack of empathic response in many parents or observers. Human beings, with our advanced cognitive capabilities, would perhaps create justifications for these actions which, again, might be spread socially through uniquely human technologies such as the Internet.
- Given the physiological arousal involved in crowd-related stress, a diminished level of incisive, specific, feature-intensive logic might be expected, in favor of less-specific, less incisive, and overly broad overarching conceptualizations of potentially important topics. In other words, we’d be more likely to be influenced by slogans and social media trends than by thoughtful considerations of logic and evidence (Sharps & Price-Sharps, 2026).
Calhoun’s studies, and those of Zuckerman, have been criticized to an extraordinary degree; the cynical scholar might be forgiven for asking how much of this criticism is influenced by emotional revulsion at the implications of the results, although there is no question that many criticisms brought against these studies are in general scientifically legitimate. It would be illegitimate, scientifically simply wrong, to apply the results of these much-criticized animal studies to the human species without substantial additional research.
However, we must acknowledge that at present there are well over eight billion people on this planet; and that modern urban and suburban environments are relatively unnatural environments with reference to normative evolutionary history. It is therefore suggested that forensic psychologists begin to research these issues with proper scientific rigor in an increasingly challenging modern world.
