The Demographer’s Folly
Author’s Note: I have returned home from extended vacation and hope to begin frequent blogs again.
Alarmists have trumpeted the end of the world for many years. Now, a simple extrapolation of continued low fertility rates in Japan predict the last Japanese person will die around the year 2600 (give or take a few hundred years). This calculation highlights a common failure of demographers in calculating future population trends. Why? It fails to consider the individual.
It is commonly known that children born to conservative parents are likely to be conservative themselves. And vice versa. Similarly, a child born to a Christian family will almost certainly die a Christian, and not a Muslim. The point is that memes for many attributes are passed on. If you also consider that the more religious a person is, the more children they tend to have, one verifiable feature comes true - fertility is ‘passed on’ from mother to son, father to daughter.
Consider a population that has 1000 people (all twenty years old) with a fertility rate of 1, and 10 people (also twenty years old) with a fertility rate of 10. For arguments sake, assume that there is no intermarriage between these two groups, and that fertility is perfectly ‘inherited’. From a demographer’s perspective, this population has a fertility rate of 1.07. Consequently we can expect that the population will continue to drop. If we consider people’s individual preferences, there will be an initial drop off in population, followed by its rapid rise.**
While these assumptions are clearly extreme, if they hold even to a small extent (Orthodox Jews have many children, and their children have many children, etc), then worldwide fertility rates may only drop temporarily rendering future predictions upon which policy is made - like how much social welfare can be afforded - wrong.
* A fertility rate of 1.07 will yield generations of approximately 1010, 540, 290, 154, etc. Using individual preferences we find generations of approximately 1010, 550, 500, 1375.