Do you know what the world population was in 1975? 4 billion. That number has almost doubled since then. How does living in increasingly dense environments influence our psychology?

PSYCHOLOGY OF DENSITY

Below is a graph of the 50 U.S. states. On the horizontal axis is average population density of the state. Can you find your own state?

What is on the vertical axis? It’s a combination of multiple indicators. Higher scores on the vertical axis mean that people in the state are more likely to (1) get a college education, (2) marry at a later age, (3) plan for the future, (4) and have fewer children. So from the graph, people in more dense states are more likely to have such behaviors.

It turns out that the same pattern emerges when comparing countries around the world. The full paper with more details is here.

What is going on here? The idea is that living in dense environments leads to greater social competition for limited resources and opportunities. And in order to compete successfully, people change their behaviors in specific ways. We spend more time and energy to build our skills (get more education), delay starting a family as a result (marry later), and also end up having smaller families. Having fewer children means that we can focus our parenting resources on fewer children (as opposed to splitting them across many children), so our children can become more competitive themselves. One might think of this general approach to life as “quality over quantity.”

And the fascinating thing is that this pattern has also been observed in some non-human animals. The theory behind this is that all organisms (including us!) have evolved to change their behaviors depending on environmental conditions. Generally, greater densities seem to trigger what is sometimes referred to as a “slower” reproductive strategy, which has a variety of implications for our psychology.

If you are interested in finding out more, here’s a summary and a Q&A about the work.