development poverty

Understanding the demographic transition

Population is one of the more heated areas of the sustainability debate. There are those who see population as enemy number one when it comes to the environment. The more of us there are, the greater our ecological impact will be. Unless reined in by deliberate policy, the emerging middle classes of developing countries will eat the planet.

Others say that since population growth is greatest in the poorest countries, consumption is the bigger problem. If one new American will have a bigger environmental impact that 25 Sub-Saharan Africans, surely we should the focus on overconsuming Westerners rather than scapegoating African mothers?

As usual, the truth is more complex than all this, but the nuances tend to get lost in all the value judgements and the long shadow of bad population policies in the past. Another big factor is the misunderstandings around why the population is growing.

Unhelpfully, we often talk about ‘baby booms’ or a ‘population explosion’, which implies a fertility problem. “People are having too many children” is the central theme of most conversations about population. But this is to misrepresent the fundamental reason why populations grow. We’re better off talking about a population transition than population boom. Here’s a useful graph:

The most important thing to notice here is that the increase in population isn’t from people having more children, but from fewer people dying. The world’s population has risen dramatically in recent decades because advances in medicine have prolonged life expectancy, and developments in agriculture have given people healthier and more dependable diets. More people are being born than are dying, and hence the increase. For all its complications, this is a nice problem to have – the alternative is people dying young.

The second thing to note is the downward curve of the birth rate – the top side of the red space in the middle. The natural consequence of a falling death rate is that people choose to have fewer children.

One of the ways in which population theorists have been wrong in the past is that they have been writing in the middle of that red section of the graph. All they see is the upward trend in population numbers, and their extrapolations point to inevitable disaster. In reality, the culture changes as people gain healthcare and sanitation and food security. The next generation will reach child bearing age and will choose to have fewer children than their parents, because they can be more confident that their children will survive into adulthood.

As the end of the graph shows, the end result of the transition is stability again. The population reaches equilibrium, where there are fewer deaths and fewer births. That’s where most developed countries are now, having passed through the transition. Many of the world’s poorest communities are on the other side of the graph – they haven’t yet seen the fall in death rates and we should expect a jump in population in those places.

Population growth occurs in the lag between the fall in the death rate and the fall in the birth rate, so the challenge for us to reduce that red space by as much as possible. That means dramatically accelerating the provision of basic healthcare, clean water and sanitation. It means addressing food security issues, encouraging greater self-sufficiency, and sharing technology and best agricultural practice.  It also means slowing the diversion of food into biofuels and meat production. Once people are at liberty to choose smaller families, we need to ensure they are able to do so, and there is a huge unmet need for contraceptives.

Once you understand the process of a demographic transition, the endless claim that “people are having too many children” starts to look simplistic. These are huge cultural shifts that play out across generations. Different countries or regions are at different points along the transition, and need different interventions. And you can’t separate population from the broader narratives of development. There’s also a host of considerations about how you  manage a demographic transition, from the youth bulge through to an aging population – but that’s a post in itself.

We need to stop arguing about whether population matters or not – of course it does. And we need to stop arguing about whether it’s a bigger issue than consumption, because that’s to reduce it to abstracts that aren’t relevant on the ground. Most of all, we just need to talk more intelligently about demographics.

  • The graph here is from the Royal Society report People and the Planet, which is a useful and balanced analysis of population and consumption. I’ll be writing more about it soon.


  1. That’s a nice theory, and I hope it’s true. I think it’s important to remember, however, that it’s an extrapolation. If you think about where we are right now, we’re still in a situation where births substantially outnumber deaths. I’d be interested to hear on what basis you think our population will reach homoeostasis in the future.

    It’s also worth remembering that if we voluntarily control our population, it will be one of the few instances where any creature has successfully done this — humanity’s record is historically poor.

    We must try — but we mustn’t be complacent.

    1. It’s not an extrapolation – as you can see, there are no dates on that bottom line. It’s not an attempt to say what’s going to happen. It’s a model that shows the basic shape of a demographic transition. A complete transition is observable in pretty much every developed country, and most countries fall somewhere within the model.

      And no, we mustn’t be complacent. I think I made that point in my conclusion.

  2. Just thinking more about that graph — it doesn’t actually make sense. Notice that on the left, it is the death-rate that fluctuates and the birth-rate is constant, whereas on the right it is the other way around (constant death-rate, oscillating birth-rate). Also, the graph is suggesting that the part coloured-red represents population increase, however, the parts of the graph where the death-rate is above the birth-rate are also coloured red. They should be recoloured some other colour, to represent population decrease.

    I understand that the graph is highly idealised, but I still think it should be internally-consistent 😉

  3. I appreciate the intent, but I’m afraid it is a lot more complicated than explained here. I don’t believe a service has been done by repeating some myths while debunking others. Rather than write a lot let me point you to these excellent recent essays with some surprising information. Take the time to read them and you’ll not get fooled again by the myths that get repeated time and again:

    Dave Gardner
    Director of the documentary
    GrowthBusters: Hooked on Growth

    1. It sure is more complicated than that, and I’m not claiming to have written the final word on the subject. The demographic transition is a general theory. It’s a pretty good one, but of course there are exceptions. It’s an observable phenomenon, but not one we hear much about, hence the post. It’s only controversial once you drill down into cause and effect, but the general shape of a demographic transition is pretty

      Looking through your links, I only see one of the ‘myths’ that I might appear to be reinforcing, and that’s the link between development and the birth rate. I’m familiar with the other arguments here, but it’s a chicken and egg situation which is not resolved as far as I’m concerned. You can put in place good voluntary population policies and help drive development. But you need a basic level of development before you can set out on that road or you’re not going to convince anyone to take part. The two go together.

      The other big factor which I’ve left out here is urbanisation. We know that when people move into cities, they have less space and have fewer children.This too is a development trend that brings down the birth rate, although it has sustainability problems of its own.

      Population campaigners tend to get upset at the demographic transition because people use it to explain away the problem. But that’s an abuse of the idea, and not what I’m out to do here. The transition exists and it’s important, but it doesn’t imply complacency.

      The transition is particularly important when you come to look at the wider demographic changes happening in society, things like youth bulges in some countries, or aging populations in others. We absolutely have to get our heads around this, or we’re going to have major social crises down the line.

      My whole point here is to reject simplistic explanations of population growth or decline, and to remember that different countries are in different places.

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