Why are Crowded City Dwellers Living the Slow Life?

What is the psychology of living in a densely populated place?  If you think of New York or Los Angeles, you might be inclined to imagine the fast life, unrestricted sexuality, street gangs, and hordes of uncaring people rushing toward a dystopian future.  But a series of studies conducted by Oliver Sng, a post-doctoral researcher at the University of Michigan, suggests a different picture – population density is associated with a slow lifestyle.

Fast versus Slow Life histories

As an undergraduate, Sng developed an interest in studying human behavior in evolutionary perspective.  Before going to graduate school to study social psychology, in fact, he spent 2 years observing a group of long-tailed macaques at the Bukit Timah Nature Reserve.  Biologists studying animal behavior have distinguished between a “slow” as opposed to a “fast” life history strategy.  A slow life history means reaching sexual maturity at a later age, having fewer offspring, and investing heavily in each of those offspring (elephants, for example, don’t begin having calves until well into their teens, and they nurse each one for several years).  This compares to a fast life history, which, conversely means producing a large number of offspring as quickly as possible, and investing relatively little in each one (some small mammals in Madagascar, called tenrecs, start having offspring a few months after birth, for example). 

Source: Oliver Sng, used with permission

Among animals other than humans, high population density is associated with a slow life history strategy.  This makes sense because if there are a lot of one’s own species around vying for resources, offspring are especially likely to need their parents to help them out. 

What about humans?

When I was a young assistant professor, I taught a class in environmental psychology, which included a section on density and behavior.  In those days, psychologists were convinced that nothing good could come of crowding.  Environmental psychology textbooks would typically describe research on what ethologist John B. Calhoun called the “behavioral sink” – a dystopic state of social pathology that resulted from crowding.  Calhoun placed a large group of rats in a 10 x 14 foot four-room enclosure, and provided them sufficient food and water to allow them to reproduce to their hearts’ content.  The prolific little creatures reproduced quite freely, and were soon as crowded as New Yorkers on a subway at rush hour.  The animals began exhibiting numerous forms of pathology, ranging from extreme social withdrawal to violence, rape and cannibalism.

Calhoun’s research was widely publicized, fueled by the implication that the behavioral sink applied to human beings as well. 

But not all the research supported this picture of density doom and gloom.  After reviewing the findings in this area, psychologist Jonathan Freedman concluded that research with human beings “has not supported earlier belief about the negative consequences of high density,” and that, in fact, psychologists had misinterpreted and overinterpreted a few dramatic and nonrepresentative studies of animals (such as Calhoun’s “behavioral sink” study). 

After Freedman’s review, research on the psychology of density became less popular.  But Sng, working with Steve Neuberg, Michael Varnum, and I, decided to revisit the phenomenon in light of later developments in life history theory.  The results were reported recently published in the Journal of Personality and Social Psychology.

The first study in the series was an analysis of archival data from different societies around the world.  In Sng’s native Singapore, every square kilometer is filled up with 7,987 people.  That is 30 times more people than you’d bump into if you took a stroll around the United Kingdom (at 261 people per sq. km.), and 249 times the density of the United States (at 32 folks per square kilometer).  Despite its extremely dense population, Singaporeans hardly live the hard-paced sexually unrestricted lifestyle, though. They are generally well-behaved and hard-working, and they invest a lot in their small families (20 percent of the national budget goes to education).  And Singapore isn’t alone in this regard.  In general, countries with higher density were found to have lower fertility rates, lower rates of teen pregnancy, longer lifespans, more emphasis on planning for the future, less promiscuous behavior, and more children enrolled in pre-school (indicative of more investment in children). These relationships held even after taking into account a variety of alternative factors, such as economic development, urbanization, and population size. This is consistent with the prediction that density would be associated with a “slower” life history in human beings, as it is in other species.

A second study compared different states in the United States, and found that states with higher density had lower fertility, less teen pregnancy, later age at first marriage, more children enrolled in preschool, more young people obtaining college degrees, longer lifespans, and more participation in retirement plans.  Again, all this is evidence for a slower life history in places with higher density.

The paper also reports two experimental studies in which people were presented with various cues to crowding, such as a news article (purportedly from the New York Times) titled “The Crowded Life: Too Many Too Much.”  The article stated that:

“…Throughout the United States, people are becoming increasingly familiar with long lines, big crowds, and giant traffic jams. There’s a good reason for all this overcrowding. According to statistics released by the U.S. census this year, population densities are growing at an unprecedented rate. In almost every U.S. state, population densities are increasing rapidly…”

Participants were then given a series of choices, such as:

“Would you prefer 1) to have $100 today, OR 2) $140 ninety days from now?”


“Would you prefer to: 1) have ONE child and invest all your resources in that one child OR 2) have MULTIPLE children and split your time and resources across all of them.” 

The results indicated that people who had been primed to think about crowding made more choices associated with a slower strategy – choosing fewer children and long-term rather than short-term payoffs, for example.

To summarize, these results suggest that human beings, like other animal species, adopt a slower life history when they are living in high density conditions.  Does this mean that everyone living in New York and Los Angeles starts having children later, has small families, and focuses on long term rather than short-term payoffs?  Obviously not.  But on average, there are relatively more slow strategists in places with high populations as compared to low populations.  It remains an interesting question why some people living in big cities still adopt a faster life history strategy.

Douglas T. Kenrick is author of:


Calhoun, J. B. (1962). Population density and social pathology. Scientific American. 206 (2), 139-150.

Freedman, J. L. (1979). Reconciling apparent differences between the responses of humans and other animals to crowding. Psychological review, 86, 80-85.

Sng, O., Neuberg, S.L., Varnum, M.E.W., & Kenrick, D.T. (2017).  The crowded life is a slow life: Population density and life history strategy.  Journal of Personality and Social Psychology, 112, 736-754. 



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