How many children are women having?

**This is the first of a few posts on population growth and climate change.**

For the human population to not decline you basically need each woman to, on average, produce more than two babies. In rich countries the figure needed is about 2.1, in poorer countries it’s a lot higher, for the simple reason that children are much less likely to reach reproductive age. In technical terms this is referred to as replacement level fertility, go above and population will increase in the long term, go below it then population will decline in the long term. Of course this only refers to the indigenous population. Population increases due to immigration can offset this.

How much does the average number of children per woman vary by country? The graph below shows average number of children per woman versus population in every country on earth in 2010. (I have logged the population axis because India and China skew it)

PopChildren

Surprisingly, there are 79 countries that average less than 2.1 children per women.

Which countries are these? Below I have plotted a word cloud of all of these countries.

image

Many of these are developed countries, which have gone through what is called the demographic transition. Exactly why birth rate is so slow is something of a mystery. In blunt Darwinian terms you wouldn’t expect women to lack fecundity when they are wealthy.

There are some surprises here. Iran averages just under 1.7 births per woman. Italian women, it would appear, do not listen too closely to advice of the Vatican. They average just over 1.4 births per woman. China’s one child policy has also put it on the list, with an average of 1.6 births per woman. Who is the lowest? Taiwan with 0.9 children per woman, though they recently boosted this a little bit.

We are also looking at a very heft chunk of humanity. Adding up the populations of all of these countries and we get a total of 3.3 billion. A simple lesson here is that when we are looking at the environmental impact of population growth it is not really a good idea to look simply at the global population. Countries vary massively in how much their population is growing, and by how much their citizens impact on the environment, in particular their carbon emissions.

(All of the data used here are taken from the excellent Gapminder website.

For the statistically inclined,the wordcloud was made using the R package “wordcloud” )

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6 thoughts on “How many children are women having?”

  1. So who’s above 7 and whose below 1? And what was the global average, about 2.4? You’ve teased me really, i was getting interested an then you stopped.

    If you are going to debunk some assumed emissions correlations at national level it is always good to start with the global fit which is quite smooth: http://tinyurl.com/bh88m2f

    Looking forward to seeing where you are headed

  2. This was Stewart Brand’s argument for encouraging development – although there are some oddities in the stats above, developed countries still dominate for low birth rates

  3. Very interesting. The work that I have yet to see is how a population transitions (back) from where it is now to a new, lower, demographically stable one. ie with an age distribution that remains constant over time. How does it arise naturally? How does anyone “engineer” it ? Required to avoid youth “explosions” or aged population “explosions”. Has parallels with neutron populations in reactor cores.

    1. You’re right, Robin, it is an interesting post, and I think you ask the same question as I would; ie, “…how a population transitions (back) from where it is now to a new, lower, demographically stable one. ie with an age distribution that remains constant over time?“.

      My thought is that I can’t see how it can. The world has developed always with a predominantly young age profile; at first because of a high birth rate and rapid decline and die-off of the infirm and old, and more latterly — since improvements in medicine at the start of the last century — because of the population explosion. Indeed I’d go as far as to say that the historical younger age profile forms almost a fundamental of current economic thinking.

      So the trick will be now to shrink back the world population to a more globally-equitable and thus sustainable level, while facing a completely new demographic where older people form a much higher percentage of the population. Thus we must all become used to being productive until the very end of our lives. It seems retirement, as it is known, must become largely an indulgence of the past.

      But I’ll be interested to see where Robert goes with this.

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