Energy Use and Population Growth

Willian Stanley Jevons was a 19th century economist who is most famous for formulating what is now known as the Jevons Paradox: technological progress that increases the efficiency with which a resource is used, tends to increase (rather than decrease) the rate of consumption of that resource.

I've just started reading the book The Jevons Paradox and the Myth of Resource Efficiency Improvements. I'll be reviewing the book itself later, but right now I want to post some thoughts that came up as a result of reading the foreword.

The foreword is by Joseph Tainter, author of the book The Collapse of Complex Societies, which is somewhat famous in doomer circles. In the foreword he discusses some areas where we see Jevons's theory at work in our everyday lives, including an interesting look at the increase in police weapons use due to the lower personal cost to the officer of using a Taser versus a handgun. One of the things he mentions in passing is the cost of raising children, with the comment that Jevons might predict that as the cost of raising kids went down we might have more of them. That made me say, "Hold on, we're seeing exactly the opposite! As societies get richer, which lowers the cost of everything including children, their fertility rates drop! What's going on?"

Then I remembered a quote earlier in the foreword, which clarified the law of supply and demand with one crucial word: "Any time one reduces the cost of a valued resource, people will respond by consuming more of it." A little light bulb blinked on. If the value the consumer places on a good drops, even lowering the price will not tempt more consumption. Perhaps the value societies place on children is changing, and that change is causing some of the drop in birth rates we're now seeing.

My hypothesis is that increasing energy use lowers the marginal value of children as labour.

To generate the hypothesis I followed this chain of thought:

One significant value of children is as workers, especially as field hands and manual labourers in less developed countries.
A child would lose that labour value as the society became richer and used more machinery to replace human labour.
As children lost their economic value there would be less incentive for parents to have them, even though their cost would decline as the society got richer.
Machinery requires energy to operate.
The per capita consumption of energy is a useful proxy for the level of a country's mechanization.
Therefore, if the hypothesis is correct, a country that used more energy per capita (lowering the need for human labour) should exhibit a lower fertility rate as the marginal value of children as labour declined.

In Wikipedia I found two lists of countries organized by Total Fertility Rate and per capita energy consumption. I plotted the values for 135 countries against each other and came up with the following graph:

The correlation is clear. Countries with high levels of energy use tend to exhibit low fertility rates, and vice versa. What this seems to imply is that increasing energy use is one of the most significant mechanisms driving Stage 3 of the Demographic Transition (possibly up to half the total influence). This relegates all the other factors such as contraception, urbanization, education, female literacy, etc. to supporting roles, as they split the remaining 50%. The primary factor in reducing population growth rates is shown to be rising energy use that displaces the value of human beings as labour.

What this finding might mean for an energy-constrained future needs more reflection, but if the hypothesis holds up there could be significant upward pressure on birth rates in such a world.
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