As more people move to a city, you’d expect about a one-to-one increase in shirts being worn, for instance, or the number of house keys issued. If something doubles as population doubles, that’s not surprising. What is unusual, though, is when something grows faster or slower than a population. That means people seem to be doing more or less of it, on average, and that could signal an interesting societal quirk.
And that’s why a new paper out of Brazil's Universidade Federal do Ceara and the City University of New York is surprising. It shows that as cities get bigger, certain kinds of death become more common, and others become less so.
For the analysis, the authors looked at car crash fatalities, homicides, and suicides in all Brazilian cities between 1992 and 2009, as well as suicides in all U.S. counties between 2003 and 2007. The authors found that if they doubled the size of a Brazilian city, car-crash deaths would also double, as predicted. But the rate of murder would grow by 135 percent—that is, homicides would more than double.
The rate of suicides, meanwhile, increased slower than population growth, rising just 78 percent when population went up by 100. A similar trend was true among the U.S. counties. There seems to be something about big cities that makes murder more likely but suicide less so.
To the researchers, this suggests that the decision to commit murder or suicide, “instead of being purely a consequence of individual choices, might have strong correlations with the underlying complex social organization and interactions.” In other words, suicide and murder aren't random; they're products of our life circumstances.
In some ways, the suicide part makes very little sense. Cities are stressful; they’re polluted, crowded, and expensive. Metropolises like New York have the ability to make people feel completely alone while surrounded by millions of people. And yet: There’s something about that dense coexistence that seems to work like a buffer against the deepest of depressions.
Social interaction makes us happier, so it's possible that big cities simply provide more opportunities to interact and share experiences. As the authors put it, "a large supply of potential social contacts and interactions might work as an 'antidote' for this tragic event. This result is consistent with the idea that human happiness is more a collective phenomenon than a consequence of individual well-being conditions."
Most suicidal people want to live, but they see no other way to escape their problems. My other theory for this phenomenon is that populous areas offer more options across the board—in access to mental-health practitioners, types of jobs, and/or the ability to find a new mate or social group—so fewer people feel like they have no other choice but to end it all.
Brazil in general has a very low suicide rate and high murder rate, but the fact that suicide rates in big American cities were similarly low seems to corroborate the Brazil data. The most suicidal U.S. cities are the relatively mid-sized and sparsely populated towns of Las Vegas, Colorado Springs, and Tucson.
If anything, this study is a bit of a double-edged sword for advocates of population density. Living in a teeming mass makes you less likely to experience inner turmoil, it seems, but more likely to want to off your neighbors. Hell might be other people, but they might just save you from yourself.
This post originally appeared on The Atlantic.