Bathrooms and the Demographic Transition Model

Bathrooms!

I’ve had students ask me about the demographic transition model, and it all comes down to one thing: toilets.

Not birth rates. Not medical breakthroughs. Not moral philosophy or religion or the Enlightenment. Toilets. Sewers. Latrines. The humble act of not defecating where you drink.

See, for most of human history, people lived in a world where having children wasn’t a choice — it was a survival tactic. You had a dozen kids and crossed your fingers that three would make it. That was Stage One of the demographic transition: birth rates sky-high, death rates even higher, and life expectancy somewhere between "short" and "miserable." Disease was rampant because nobody understood where it came from. Famine, war, dirty water — it was all part of the background noise of daily life. If the rats didn’t get you, the typhus might.

Then, slowly, almost accidentally, everything started to shift. That shift is Stage Two, and it didn’t start in a biology lab — it started in the gutter. Literally. The invention of public sanitation systems, sewers, and eventually toilets meant that the biggest killer of all — contaminated water — was finally being tackled. People started living longer, not because they were suddenly healthier, but because they were no longer being killed by things in their own drinking supply. Death rates dropped. But the birth rates? Those stayed high. Because it takes a while for culture to catch up to plumbing.

That lag created a population explosion. More people living longer, still having loads of kids, and suddenly cities were bursting at the seams. That was Stage Two’s trademark: massive population growth, entirely thanks to a few basic public health interventions. Again — toilets.

Now, enter Stage Three, and this is where it gets interesting. As countries industrialize and urbanize, people start realizing that kids are no longer economic assets — they’re expenses. School becomes mandatory. Women get more education and more say in whether or not to have children at all. Families shrink. Birth rates fall. And just like that, the runaway population growth starts to slow down. Not because of a plague or a war, but because people are making different decisions.

Stage Four? That’s the fully industrialized world. Birth rates and death rates both low. The growth curve flattens. The problem now isn’t too many people — it’s not enough. Aging societies with shrinking workforces, struggling to fund pensions and healthcare. Robots start looking less like a novelty and more like a necessity.

Some argue there’s a Stage Five, where populations actually decline. Countries like Japan, South Korea, and Italy are leading the charge — not by design, but by default. People just aren’t having kids. Some don’t want to. Some can’t afford to. And the whole economic structure starts to look a little wobbly.

So when students ask me how we got from a world of mass infant mortality to one where the biggest demographic problem is not enough babies, I don’t start with economics. Or politics. I start with waste. With the decision to keep human filth out of the water supply. Because once that problem was solved, everything else — the falling death rates, the rising life expectancy, the shifting birth rates, the whole demographic transition — came downstream, so to speak.

In the end, it’s not just a chart about population — it’s the story of how toilets quietly changed the course of human civilization.