The great Muslim TFR mystery

I first heard about the population explosion when I was a stripling of 15. Our Year 9 geography teacher told us that global population would reach 8.5 billion by the year 2000. Back then, in 1960, it was less than three billion.

Well here we are in 2012 and global population stands at around 7 billion. We're unlikely to reach 8.5 billion before 2030 at the earliest. The population has exploded but not nearly as fast as was predicted.

So what happened?

Population growth rates in any one country depend primarily on four factors:

(1) Proportion of women of child bearing age

(2) Average lifetime number of babies per woman. This number is called the total fertility rate and is abbreviated to TFR

(3) Net migration

(4) Death rates

For the Earth as a whole we can probably forget the third factor. So far as we know there is no net migration to Earth from Mars, Alpha Centauri or anywhere else.

Longevity is increasing in most countries so age-adjusted death rates are all falling.

The really important number is TFR. A TFR of 2.1 under modern conditions is usually considered replacement level. With a TFR of 2.1 each cohort of women will just replace itself.

It was not always thus. In mid-eighteenth century London, for example, replacement level was somewhere between three and four. Child mortality rates were much higher then.

But for now let's consider 2.1 a replacement level TFR.

Even with a TFR below 2.1 population could still go on growing for a while. This happens when, due to previous high birth rates, there is a large cohort of women of child-bearing age. We see this in China which has had a below replacement level TFR for many years but where the population is still growing slowly. It should stabilise in the next few years and then start declining because the present cohort of women is not replacing itself.

TFRs have been declining across the world for 50 years at a rate no one back in 1960 thought possible. Currently no European country has a TFR above replacement level. The closest seems to be France where TFR is boosted by a large population of immigrant origin from countries that traditionally have high TFRs.

However, here is the kicker. Which group of countries has seen the most spectacular fall in TFR?

It will come as no surprise to learn that the greatest falls in TFR have occurred in poor countries. These are the countries that had the highest TFRs to begin with.

However there are large regional variations.

Take a look at the table below. It shows TFRs in 1960 and 2011 for a selection of countries and regions. The first number shows TFR in 1960 taken from World Bank Development Indicators. The second number is TFR in 2011 from CIA World Factbook.

Bangladesh: 6.72 --> 2.55
Egypt: 6.60 --> 2.94
Indonesia: 5.67 --> 2.23
Iran: 6.94 --> 1.87
Iraq: 6.25 --> 3.58
Malaysia: 6.31 --> 2.64
Morocco: 7.17 --> 2.19
Pakistan: 6.65 --> 3.07
Saudi Arabia: 7.22 --> 2.26
Syria: 7.47 --> 2.85
Turkey: 6.12 --> 2.13
Yemen: 7.29 --> 4.45
World: 4.92 --> 2.47
Brazil: 6.21 --> 2.16
China: 5.67 --> 1.55
India: 5.87 --> 2.58
Sub Saharan Africa: 6.62 --> 4.90

You will notice that the first 12 countries in the table are all Muslim countries. It includes all the biggies.

So here is the great Muslim TFR mystery.

The theory is that traditional Muslim societies in which women are repressed should have persistently high birth rates. Yet when we look at the data it hasn't happened. Muslim societies have experienced precipitate declines in TFR. Even in outright theocracies like Iran and Saudi Arabia TFRs in 2011 were less than a third their level in 1960.

All the Muslim countries in the table had TFRs above the global average in 1960. By 2011 Indonesia, Iran, Morocco, Saudi Arabia and Turkey were below the global average.

In 1960 all 12 Muslim countries in the table had TFRs well above replacement rate. By 2011 Iran was below replacement, Turkey was effectively at replacement and Indonesia, Morocco and Saudi Arabia only marginally above replacement.

And yet as recently as 2000 Saudi Arabia had a TFR of 4.01!

Yemen's trajectory is especially interesting. Its TFR actually peaked at an improbable 9.22 in 1984 before dropping to the current relatively low level of 4.45.

For the world as a whole TFR has halved between 1960 and 2011. In this group only in Iraq and Yemen is TFR in 2011 more than half the 1960 level.

By some measures Muslim countries have experienced a greater fall in TFR than most countries at a similar stage of development. Certainly there is no evidence that Muslim countries' population growth rates are stuck in high gear.

Why TFRs should have declined so precipitately among Muslim countries is something of a mystery. Perhaps it is because most of them had anomalously high TFRs to begin with and are now reverting to the mean.

No one knows whether the downward trend in global or Muslim TFR will continue or perhaps reverse course.

As the man said:

A trend is a trend
But the question is; when will it bend?
Will it alter its course
Through some unseen force
And come to a premature end?

What is certain is that when it comes to human beings the only certainty is uncertainty

And sociologists' theories about population, or anything else, aren't worth the pixels.