In the UK we’re familiar with the practical implications of increasing population density: traffic jams, longer waits to see a doctor, a lack of available housing. What many of us probably hadn’t realised is how living in crowded environment could be affecting us at a deep psychological level, fostering in us a more future-oriented mindset or what evolutionary psychologists call a “slow life history” strategy.
In their paper in the Journal of Personality and Social Psychology, Oliver Sng at the University of Michigan and his colleagues present a range of evidence that shows how this strategy plays out in the more patient ways that we approach our relationships, parenting and economic decisions. In essence, the researchers are proposing that the presence of greater numbers of other people in close proximity prompts us to invest in the future as way to compete more effectively.
The idea behind life history theory comes from observing variations in behaviour between and across species, mainly in terms of how they approach reproduction. Species with longer life-spans that live in greater population densities tend to favour more investment in fewer offspring who take more time to develop. In contrast, species living in lower densities and at great risk of predators tend to favour a short-term strategy, for example having as many offspring as early as possible in the hope that at least some will survive. There’s also evidence that the same species, such as Chinook salmon, adjust their mating strategies to the short- or long-term depending on the kind of environment they’re in.
To test how this might play out with humans, Oliver Sng and his team began by comparing the population densities of countries around the world with a range of parenting and relationship-related outcomes. They found that people in more densely populated countries tend to plan more for the future, have fewer children, have them later, invest in more long-term relationships, and place a greater emphasis on education (this pattern held even after accounting for between-country differences in urbanisation, economic development and population size ). The same pattern also applied across US states: those with greater population density expressed a more future-oriented focus, a “quality over quantity” approach in terms of relationships and child-rearing, and placed more importance on education.
There are problems with how to interpret this kind of correlational data (for instance, there could be unknown factors involved) so the researchers also conducted some experiments. They found that asking participants to read an apparent New York Times story about increasing population density in the US led them to favour future financial rewards over more immediate gains in a simple economic game. Listening to the soundtrack of a large human crowd, as opposed to white noise, had a similar effect.
The researchers also showed that the effects of population density reminders seem to be specific to our stage of life. When undergrad students read the New York Times article about America’s increasing crowding, as opposed to an article about rising squirrel populations, they tended to say they favoured investing more in fewer relationships, but their answers about how many children they wanted, or how much they prioritised education, were unaffected. In contrast, reading about increasing population density led an older group of participants (average age 30) to say they favoured investing more time and effort in having fewer children.
Sng and his colleagues said their results are preliminary: we need more data to confirm these effects and also to explore the potential mechanisms behind them. They believe many mechanisms are likely at play, including population density affecting our hormones and brain development, our motivations (for example, leading us to realise that we need to increase our chances of competing successfully in future), and cultural norms, for example mores around sex and relationships. “Much remains to be examined,” they concluded. “We hope this initial foray will generate renewed interest in a topic that has been all but forgotten, and encourage the field of research on density to become a little more crowded.”
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