Comment by a-priori | Hacker News Reader

Comment by a-priori | Hacker News Reader

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The world population is not experiencing exponential growth. It's experiencing logistical growth (i.e, following a logistical function rather than an exponential function). We've just been seeing the first half of the curve, which does approximate exponential growth.

But we're starting to see it turn around. In the most developed countries, fertility has dropped to replacement or lower. As the remaining countries develop, their fertility rates are also dropping. It's reasonable to extrapolate from this that at some point in the future, the global fertility rate will be at or below replacement.

The constraints are microeconomic. It's expensive to raise children, especially when you factor in opportunity costs (this part is key to why world population won't stabilize at starvation levels). When you give people birth control, people seem to make a rational economic decision about how many children to have. That provides the feedback mechanism you mentioned.

The developing world has birth control but, in large parts of it (e.g. most of africa), most people aren't using it. This is for economic reasons. In these economies children are your pension fund. There's no RRSP funds or old age security payments. Just children who (hopefully) look after you in your old age. If you have only one or two you will either be an unreasonable burden upon them or simply be abandoned to starve.

The economic support system for seniors in the developed world is currently under a lot of strain too. In countries where pension funds are funded from current taxes the baby-boomer retirement is going to be a tremendous drain on society. The baby-boomer generation should have tucked away a nice huge fund to pay them in retirement as well as support the greater demand on the medical system. Instead, they racked up huge amounts of public debt. Massive amounts of immigration and raising the retirement age have been the stop-gap measure of choice so far, but the developed world's support for senior citizens could easily revert to that of the developing world's without much warning!

So, yes, children are expensive, but for most of history and in large parts of the world today they are a necessary investment for retirement. In only the developed world of the past century have financial pressures favored fewer children, and that could easily change.

fertility rates are dropping worldwide. At some point in the next 30 years, it is expected to fall below replacement level.

Check out this graph comparing fertility rates. China and Iran (!) now have fertility rates below that of the U.S.

http://www.google.com/publicdata/explore?ds=d5bncppjof8f9_&#...

Curiously, rates for Italy and Germany are separated from other developed countries by about .5% http://www.google.com/publicdata/explore?ds=d5bncppjof8f9_&#...

The developing world has birth control but, in large parts of it (e.g. most of africa), most people aren't using it. This is for economic reasons.

I would argue that in many, if not all, of these places this is instad due to poor education, misinformation or religious opposition.

Edit to add: It's also important to distinguish when men have access to birth control and when women have access to it. Fertility rates won't drop until women can control how many children they have.

> But we're starting to see it turn around. In the most developed countries, fertility has dropped to replacement or lower. As the remaining countries develop, their fertility rates are also dropping.

And in the most developed most-developed countries, that has reversed: http://www.nature.com/nature/journal/v460/n7256/abs/nature08...

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