If you are like me, you’re worried about the increasing amount of aggression displayed by people, both at home and abroad. School-yard and urban shootings, coupled with civil and jihadist wars, don’t make for calming nightly news.

So I’m going to go out on a limb with this blog, to suggest that these aggressive human behaviors derive from the stress of overcrowding in a world of rising human population.

Forty years ago, the population biologist, Charles Southwick, alerted us to the difference between high density and crowding. Some populations can persist at high densities if there is plenty of food, water and shelter. Others show the stress of crowding, even at lower densities, when these resources are in short supply and the news thereof is rapidly communicated through the population. And, Lord knows, with modern social media, the news anywhere is distributed everywhere within seconds.

In his earlier work, Southwick had shown direct correlations between the population density of house mice and aggressive behavior, increasing mortality of young, and deviant sexual behavior. Crowding leads to increasing stress, changes in hormonal levels, hypertension, and declining health. As we crowd ourselves in cities, we are increasingly disconnected from nature and the mental refreshment that nature offers.  As in other species, our increasing population numbers lead to mass migrations to new potential habitats.

So, when I look at the civil war in Syria that has caused massive human migrations of desperate people, I wonder just how much of their misery is derived from a decade of crop failures and droughts in that region, coupled with one of the highest rates of human population growth in the world. At least one study has linked drought in the Middle East to the impacts of global climate change, wrought by human emissions from fossil fuel combustion.  Climate change lowered the carrying-capacity of the environment, creating crowding and its associated syndrome.

Closer to home, when I look within my own country, I wonder just how much aggression amongst the youth is coupled with the perception of an increasing gulf between rich and poor and diminished expectations that the future can bring a better life. The aggression is enhanced among those who believe that resources are concentrated amongst those of differential privilege. It is hard to know just what causes a disturbed young man to engage in the mass shooting of children and students, but my suspicion is that such individuals find it difficult to find a place in a crowded world of individuals who are each aggressively seeking a share of a limited resource pie.

There is no good metric for crowding—no convenient “crowd-meter.”   But the behavior of humans offers an indirect measure of our increasing crowded planet.

Efforts to stabilize our population are long overdue.

References

Kelley, C.P., S. Mohtadi, M.A. Cane, R. Seager and Y. Kushnir. 2015. Climate change in the Fertile Crescent and implications of the recent Syrian drought.   Proceedings of the National Academy of Sciences 112: 3241-3246.

McHarg, I. 1969. Design with Nature.  The Natural History Press, Garden City, New York.

Miranda, M.L., D.A. Hastings, J.E. Aldy, and W.H. Schlesinger. 2011. The environmental justice dimensions of climate change.  Environmental Justice 4: 17-25.

Southwick, C.H. 1971. The biology and psychology of crowding in man and animals.  Ohio Journal of Science 71: 65-72.