Do you remember when Dan Brown could write a book based on our fears of overpopulation, name it after Dante’s Inferno, and then make a stash of cash? Well, it seems that economist fears are now moving in the opposite direction. Underpopulation, falling fertility rates, demographic cliffs: they’re the new population buzzwords.

The problem is math:

1. Where each pair of adults have more than two children over their lifetimes, they are adding to the population. And this can be exponential: because if their children go on to bear more than two offspring per breeding couple, then they’ll be increasing the multiplier effect.
2. But where couples have fewer than two children over their lifetimes, then they are failing to replace themselves.

And in today’s world:

1. Millennials in first world countries are tending to wait to have kids, if they have kids at all.
2. Countries like China and India are stuck with larger populations of men than women, due to things like one-child-policies and gender-selective abortions.

So we face a future, largely of our own making, in which:

1. longer lifespans are making it look as though our population is increasing (because we’re adding people and delaying the death subtraction); but
2. eventually, old age will catch up with us; and
3. when that happens, we’ll have smaller younger generations to support the elderly.

Falling Fertility Rates

Here’s a graph that shows how many nations are not having enough children to maintain their population sizes:

And here’s one showing falling fertility rates:

The main implication here is that the future work force is going to be smaller, while the number of dependents on that workforce is going to increase.

Work Forces and Elderly-Dependency Ratios

That shrinking population of workers:

The growth in the number of elderly dependents:

And this will have its own demographic multiplier effects. For instance, if you have young couples supporting aged parents and grandparents, then they might be less likely to have children themselves – and we might accelerate the depopulation process.

Also, this doesn’t take into account concerns like climate change and the rise of antibiotic resistance – which might do us in long before we even reach the point of being concerned by underpopulation.

Either way, I’m strangely comforted by this sudden reversal of panic stations. It reminds me that there are sometimes natural forces of balance that assert themselves while we’re not paying attention.

Rolling Alpha posts opinions on finance, economics, and sometimes things that are only loosely related. Follow me on Twitter @RollingAlpha, or like the Rolling Alpha page on Facebook at www.facebook.com/rollingalpha.