Population Size and Post-apocalyptic Fantasies

There’s a persistent narrative in America about collapse involving a small band of heroic individuals surviving through a relatively short hard time to rebuild the human species. Sometimes, “relatively short” means only a few days, while sometimes it is as long as a generation, but the band of people is never bigger than perhaps a thousand people, and quite often, the group is quite small.

The truth is that it would take a population of at least 2500 people to save humanity from a long decline ending in total extinction. Corey Bradshaw does a nice job summarizing the situation in Why populations can’t be saved by a single breeding pair. Keep in mind that this isn’t just 2500 people on Earth, but rather, 2500 people who are part of the same general community or a bunch of separate communities that regularly visit one another. The 2500 have to interact with one another regularly. If there are 1000 in China, 500 in the US, and 1000 in Argentina, that doesn’t count.

In the US, I think the belief that a single breeding pair can re-establish humanity comes from three places: 1) A literal interpretation of the Bible, with all the inbreeding that it implies, 2) Hollywood budgets that limit the size of groups in apocalyptical and post-apocalyptic stories, 3) Lack of understanding of population genetics. I’m not an expert in population genetics myself, but I choose to trust people who have studied the subject in depth.

This is just one misunderstanding about the survivability of the coming collapse of this civilization. Others include the complexity of modern technology, the cognitive capacity of people who are struggling to merely survive, the post-collapse availability of dense energy sources (like oil), the rapid oscillation of climate on a planet that is re-establishing equilibrium after a destabilizing event (anthropogenic climate change), and the genocidal ambitions of those who typically own weapons. In short, there isn’t going to be a happy ending after a period of turmoil.