Jason Collins reviews Eric Kaufmann’s Shall the Religious Inherit the Earth?: Demography and Politics in the Twenty-First Century.
To give a sense of the power of this higher fertility, the Old Order Amish in the United States have increased from 5,000 people in 1900 to almost a quarter of a million members. In the United Kingdom, Orthodox Jews make up 17 per cent of the Jewish population but three-quarters of Jewish births.
…Kaufmann’s case worries me more than tales of government deficits due to demographic change. Even if you assign a low probability to Kaufmann’s projections, it provides another strand to the case that low fertility in the secular West is not without costs.
The numbers cited about Orthodox Jews in the UK struck me as fishy, based on what I know about the U.S. Suppose that there are 80 non-Orthodox Jewish women and they each have one child (a really low fertility rate), for a total of 80 non-Orthodox Jewish births. Then suppose you have 20 Orthodox Jewish women, and they have to account for 3/4 of all Jewish births, which means that they need to give birth to 240 children, or an average of 12 children each. There are in fact several sub-groups within Orthodox Judaism, and there are some sects in which families of that size are common, but there is no way that the average family size of all Orthodox Jews is 12 children.
There is a larger objection that I have, which is that the high growth of the fervently religious starts from a low base. Assume that non-fervent women have one child each, and fervent women have ten children each. If you start with 999 non-fervent women for every fervent woman, it is going to take quite a few generations for the fervent to “inherit the earth.” Meanwhile, much else will change.
[UPDATE: In a comment, Megan McArdle points out that the arithmetic in the above example leads to the fervent reaching parity in 3 generations, and then soaring to dominance thereafter. But as she points out, the discrepancy in fertility between the fervent and non-fervent is not as wide as in the examle. And if nothing else, I can fall back on “much else will change.” By the end of this century, we could very well see dramatic changes in medical science, including reversal of aging and cloning.