The human population on this little blue-green pearl we ride around on has been increasing since there have been humans. It's something we've assumed for some time will continue, and quite a few pearl-clutching books and essays have been written about the dangers of human population growth. But now, at least in the developed world, the human population is cresting - and over the next hundred years or so, will actually start to decline. Key distinction: in the developed world.

For everyone alive today, the present population boom is all we've ever known. But as the above chart shows, a bust seems all but certain later this century as birth rates fall across the world.

Fixated as we are on the here and now, the population peak that's coming might seem totally unprecedented. In a new paper published to the Proceedings of the National Academy of Sciences, anthropologists from various institutions across the United States share some needed perspective. In fact, exponential expansions and occasionally jarring recessions have defined human population growth for tens of thousands of years.

You can see the abstract of the paper here.

This is not, however, a universal phenomenon. That is key, and here's why, and I'm going to tell you: This decline in the rate of population growth, and the eventual population decline, is something we are seeing in the developed world and, to some extent, in the developing world. In particular, Russia, China, Japan, and much of Europe — at least, ethnic Europeans — are about to fall off a demographic cliff, and in the next hundred years or so, the face of humanity on planet Earth is going to change a great deal.

The reason for that is that there are places where the human birth rate is still increasing, sometimes dramatically.

See Related: Birth Rate in Freefall as 1 in 4 Americans Puts off Having Kids Due to Climate Fears 

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Here are the top ten nations, as far as birth rates: Niger, Angola, Democratic Republic of Congo, Mali, Benin, Chad, Uganda, Somalia, South Sudan, and Burundi.

What do those ten nations have in common? They are all third-world nations with astronomic poverty rates, with large portions of their populations living at the subsistence level. Children in societies like this are a combination of free labor and old-age security, whereas, in modern, developed nations, children are an expense. They are an expense that most people happily take on, as children bring joy and meaning to our lives, but they are nevertheless an expense.

It would be easy to bemoan the death of the developed world; as the saying goes, the future belongs to those who show up for it, and much of the developed world just isn't showing up. But there is also an opportunity here. A large part of what makes the developed world, you know, developed is (relatively) low corruption, free markets, and private property. Those are the keys to prosperity in a society, and those are the attributes that the third world needs to adopt to achieve lasting prosperity. Of course, there is very little indication that these nations are about to suddenly realize the blessings of liberty; it is those blessings, not raw numbers, that are likely to change the way the human population on this planet looks in generations to come.

The world is going to look very different in 150 years. But then, it looked very different 150 years ago. Any predictions we might make in this field of discourse are largely guesswork.