Tag Archives: humans

Population density and the spread of humans

Tim De Chant at Per Square Mile comments on a study on the relationship of humans ability to tolerate, and benefit from, living in dense groups and the advantages that conferred for our species “colonization” of the globe.

Density itself wasn’t directly responsible for the first forays out of Africa. Those groups were were too small and dispersed to receive a substantial boost from density. They faced the worst the natural world had to offer, and many probably couldn’t hack it.

Where population density conferred its advantages was when subsequent waves of colonizers followed. Density allowed those people to thrive. They joined the initial groups, growing more populous and drawing more resources from the land. This made groups more stable both physically and socially—full bellies lead to happier and healthier people. As each group’s numbers grew larger, their social bonds grew stronger and their chances of regional extinction plummeted. In other words, once people worked together to establish themselves, they were likely there to stay.

The degree of our sociality has allowed us to bend the curve of population density in our favor. If early humans had been an entirely selfish species—each individual requiring as much or more land than the previous—β would be equal to one or greater. We wouldn’t have lived at higher densities as our populations grew, and early forays beyond the savanna might have petered out. Instead of conquering the globe, we’d have been a footnote of evolution.¹

And here is where we can consider how this affects our modern lives. Population density may have aided our sojourn out of Africa, but it’s clear there are limits. Hunter-gatherer populations appear to be limited to around 1,000 people, depending on the carrying capacity of the ecosystem. Technology has raised carrying capacities beyond that number—as evinced by the last few millennia of human history—but we don’t know it’s limits. A scaling exponent equal to ¾ may have helped our rise to dominance, but it also could hasten our downfall. Technology may be able to smooth the path to beyond 7 billion, but what if it can’t? What if ¾ is an unbreakable rule? What happens if we reach a point where density can no longer save us from ourselves?