I have spent my entire adult life worried about overpopulation. What is the carrying capacity of Earth? At what point will we have a massive die-off? Will there be anything like wilderness left by the time that happens? Enough biodiversity left to adapt to climate change in a way that will be tolerable for humans? Etc etc. Just look at a chart of human population growth and it’s clear that we are in the upswing of a human version of the algae bloom/die-off.

And maybe we are, but I just listened to two Seminars for Long-Term Thinking focused on population, Stewart Brand’s “Cities and Time” and Philip Longman’s “The Depopulation Problem” and I’m thinking differently about it now. It’s looking very likely that our population has doubled for the last time, and most of the rest of our population growth is going to be in old people, not babies. People are living longer and having way fewer kids.

There are a few reasons for the radical shift in population-growth rate. First is urbanization. People are flocking to cities in massive numbers, and in the city, kids are no longer an economic asset like they are on the farm. In economic terms, if you are in the city, you are probably better off without them. Second is feminism, or at least it is a phenomenon feminists are in favor of. Women are getting educated, working, and more in control of their reproduction, so they are having fewer babies. (This is arguably another result of urbanization–if you’re on the farm, women are most economically valuable for making babies. If you are in the city and kids don’t matter so much, why not have that second income?) Third is television. Philip Longman called this phenomenon “TV taking the bandwidth out of the bedroom.” Birth rates are inversely proportional to hours of TV watched. This may be because it is urban, small families that are idealized in TV shows.

Stewart Brand’s version of the story is the more optimistic: Perhaps this means we humans have a shot at long-term survival after all. City living is greener than country living–way smaller ecological footprint per person. We still have to weather the population peak without ruining the planet as a habitat for ourselves, which will be no small feat, but at least there might be light at the end of the tunnel!

Philip Longman’s version is pretty depressing: The only population group able to withstand this small family trend are those who are highly principled, anti-materialistic, and dogmatically in favor of big families: religious fundamentalists. Liberals are a dying breed. Fundamentalist populations are burgeoning. The future looks very conservative and patriarchal. And, since we can now tell the sex of our kids before they are born, it means we will have fewer and fewer women–that is to say, more and more females will be aborted. This is already happening in China, where the sex ratio has reached 6 men for every 5 women. With women a scarce resource plus a highly patriarchal society, and the outlook for women’s freedom does not look good. On top of that are the economic problems that come along with an aging population with fewer and fewer workers to sustain it. We are about to get a small taste of that with the retirement of the Baby Boomers. Over the next 100 years that situation will be global and on a much bigger scale. The poverty and desperation that will produce will put ecological concerns on the sidelines, making Stewart’s version of the story unlikely. He advocates governments giving incentives to have kids, but says that it hasn’t worked at all in countries that have tried it.