Where The Girls Are

You may or may not believe in the theories propounded by Mark Steyn and others as to the powerful effects that demographic changes will have on the future of the world in general and the relative balance of power between Europe and the Muslim world in particular, but there’s no denying that demographic trends are a powerful historical force that influences every other aspect of the world – quite simply, you can’t look meaningfully at what the people want or are capable of doing until you know who the people are. A nation’s people really are it’s most important resource, without which all other resources, from capital to natural resources to strategic location, will lie fallow or fall to other hands.
There are a lot of different ways to slice the demographic data. Steyn often uses birthrates to explan the dramatic differences between growing populations in places like Yemen and rapidly aging and shrinking ones in the old Soviet Union and Western (especially southern) Europe. But while the birth rates are probably the best data point, I fear that some observers tend to write them off because they are trends, and trends after all can change.
Another way to look at the numbers, though, is that once a year is over, there’s a fixed number of children born in a country, and while you can add more by immigration – which in many cases changes the fundamental nature of the population if done in numbers large enough to move the needle, trend-wise – and you can subtract for infant mortality or other calamities, basically you have a hard, fixed, historical number. Russia can increase it’s 2009 birthrate but it can’t change the number of children born in Russia in 2006 – and that number will be part of the baseline for future population growth or decline. Trends plus time equal history.
What follows is a look at some of those hard numbers.

In measuring potential for the future population of a country, the most important number is how many young women will be of childbearing age at any particular point in time. While young people of both genders have a variety of contributions to make (the number of young men, specifically, tends to be useful in projecting a country’s immediate miliary capacity), but the most basic fact of life is that only women can give birth to the next generation, and they do so one child at a time (unlike young men, who of course can at least in biological terms father large numbers of children per year). So for the purpose of projecting the limits imposed by current reality on future population trends, the best metric is the number of little girls, who will grow up in time to be the mothers of the next generation.
Using the 2007* figures from the CIA World Factbook, here are the top 35 countries (plus the EU, which the Factbook gives a listing separate from its member states) ranked by number of girls age 15 and under, along with each nation’s current population rank.
You can see how dramatically some of the rankings are changing, and in particular how implacably the population of India is pulling away from the pack. At the same time, recall that some of the fastest-growing youth populations are in desperately poor countries where poor health conditions impose a cap on growth – I’ve marked with an asterisk any country with infant mortality rates above 75 per 1000, as those countries are likely to see less long-term growth than the number of young girls would otherwise indicate. For now, at least, I’ll present the data without a lot of additional analysis.

Among the top 51 from 2007 (the ones above Yemen), the following countries didn’t make this list, with the rough number, in millions, for girls 15 and under:

What would be the economic impact of population growth? Well, that’s much more speculative, but let’s just, as a back-of-the-envelope estimate, look at what happens if you take the numbers in the chart above and multiply them by current per-capita GDP numbers. Note that this isn’t a ranking of the whole world, just of the countries in the top chart, and it’s not total GDP, just GDP per capita multiplied by the number of young girls:

The effects here may not seem like a dramatic shift in the global balance of power, but when you then factor in how population changes as well as pre-existing trends are likely to affect per capita GDP, the picture can get a good deal more interesting.
* – I ran these numbers a few months ago; only in the last week or two did the site update to 2008 numbers.