The Impact of Population Growth
Tim Dyson


Editors Introduction
One hundred and fifty years ago life was very insecure in Western Europe. Birth and death rates were high and life expectancy was low: a quarter of children might die before their first birthday, and famine or epidemic frequently decimated populations. Since then, Western Europe and North America have gone through a demographic transition that has radically transformed our lives and the world we live in. In this interview Tim Dyson, professor of population studies at the London School of Economics and Political Science, discusses the demographic transition throughout the developed and developing world, and considers the invisible yet powerful forces of population growth and decline, of mortality and birth rates.

Could you outline the main population trends in the world today?

Tim Dyson: The countries of the world can be divided into three broad categories. First, there are those countries where birth rates are still high--about 35 or 40 births per 1,000. These sorts of populations are to be found in northern parts of the Indian sub-continent and large areas of central and west Africa. The populations in such areas are growing fast. They are young populations with high birth rates: In parts of sub-Saharan Africa populations are growing at rates of 2.5 or even 3 percent per year. Although birth rates are still high, they are in general decreasing in this category of country, but it is going to take several decades before they reach acceptably low levels.

At the other end of the spectrum are countries with very low levels of fertility. These include most of Europe, Japan and, to some extent, China. On average, in these areas women have two or less live births each. Their populations are fairly old--they are going to age increasingly as the decades go by--and they are not growing very fast. In fact some of these populations would be declining were it not for a certain amount of in-migration.

The main contrast between these two types of population is that the first group have high fertility and the second group have very low fertility. Virtually the whole world is moving from the high group to the low group, so most countries fall somewhere between the two.

There is one other broad group of countries that I think has to be identified nowadays. This is the group of countries badly affected by HIV/AIDS. The countries worst affected are in sub-Saharan Africa, particularly in eastern and southern parts of sub-Saharan Africa. They have increasing death rates, and in many of them life expectancy has reduced very substantially. Many of them also have declining birth rates, and as such are moving towards a situation of zero population growth. However, this is due to a very particular event: namely the HIV/AIDS pandemic.

What factors influence the decline or increase in population growth rates?

Dyson: In small countries migration can be a very important factor. The smaller the population, the easier it is for in-migration or out-migration to have a significant effect on whether the population is growing or shrinking. In very large countries, such as China or India, in- or out-migration has virtually no effect on the rate of population growth, simply because the populations themselves are so large that even the out-migration of several million people has a negligible impact on the overall rate of population growth. However, migration is very variable from country to country.

The main factor that differentiates populations around the world is the birth rate. In parts of sub-Saharan Africa and North India, women have on average five live births. That means that birth rates are very high. Death rates everywhere have declined quite substantially in the last 40 or 50 years, so these populations are growing, essentially because of the high birth rates. A key issue for the future is how fast birth rates come down in different populations.

The improvement in mortality applies in virtually all developing countries as well. For example, life expectancy in India at independence in 1947 would have been slightly over 30 years. Today it is more than 60 years. This means life expectancy has almost doubled in the space of 50 years--a tremendous improvement. Most countries in sub-Saharan Africa were also experiencing improving mortality and death rates until the advent of the HIV/AIDS epidemic, which is a very particular tragedy. If you look at developed regions of the world, such as Europe, Japan and North America, life expectancy has continued to climb and is, in general, still going up.

What impact has demographic growth had?

Dyson: It is probably best to divide this question into two. We can consider the impact of demographic growth on individual countries and then on the world as a whole.

In the context of the world in which we live, there is a general view (at least among demographers) that rapid population growth is problematic for poor countries. It means that governments have to provide more schools and more jobs for constantly expanding populations of children and people of working age. One of the great advantages of a slower rate of population growth is that, rather than building more schools for servicing an increasing number of children, you can commit resources to improving the quality of education that children get. Eventually, one of the advantages of slower population growth is that governments don't have to produce quite so many jobs. Thus for very poor countries rapid population growth poses major challenges from an economic perspective.

However, rapid population growth can pose a number of other serious challenges. If one ethnic group is growing or thought to be growing faster than another ethnic group, it can lead to political turmoil. Also, in some parts of the world there is no doubt that rapid population growth has contributed to environmental deterioration. For example, in parts of sub-Saharan Africa there has been very little increase in agricultural yields, even though populations are increasing, so the only way they can produce more food is to bring areas of forest or savannah into agricultural use.

Another aspect of population is urbanisation. Urbanisation tends to proceed as the demographic transition occurs. The developing world has witnessed the rise of rapidly expanding cities, which might be growing at rates of 3 or 4 percent per year. These citizens require housing, sanitation, water supplies, electricity ... the list goes on. The challenges surrounding the provision of urban infrastructure are absolutely immense.

When I was born the total population of the world was about 2.5 billion. The world's population now is over 6 billion, and it will probably increase to something approaching 9 billion. In my lifetime we have been adding an extra billion people about every 13-14 years; yet when I was born, there were only 2.5 billion people on the planet. This does have, I suspect, major consequences at the global level--not so much in and of itself, but combined with the fact that, as populations develop, they use more and more energy. In other words, I think that demographic growth at a global level is problematic if you couple it with the levels of energy that we consume. I hasten to add that it is the rich populations of the world, such as Western Europe and North America, that burn a lot of oil, coal and fossil fuels, and make a large contribution to the phenomenon of global warming. Increasingly, however, development in the rest of the world means that populations there, quite reasonably, will follow similar paths, perhaps with greater efficiency than we did in the past, but nevertheless they are going to be burning more fossil fuels too. So when considering what the problem for population growth at the global level is, I think we must take into account the increased levels of energy use. We may well be facing severe challenges in the decades ahead, as many people realise.

What is the demographic transition? Has it had any broader consequences for society as a whole?

Dyson: I do think it's important to define the demographic transition. If we go back 150 years in Western Europe, birth and death rates were high (30-40 per 1,000), life was very insecure and women had high levels of fertility. If you look at much of the developing world, those sort of conditions applied 50 or 60 years ago. The demographic transition is the process whereby death rates drop, the population starts to grow and, after a delay, the birth rates come down as well. Given a hundred years, you find that birth rates and death rates are both low. So the demographic transition is the transition from high birth and death rates to low birth and death rates. Western Europe and North America have come through the demographic transition. Many countries in the developing world are still going through it.

The implications of this transition are absolutely huge. One of the things that occurs as populations go through it is that they start to urbanise. From having a relatively small urban sector, the demographic transition brings about the urbanisation of the population. Whereas in Africa today, 20 percent of the population live in cities, in Western Europe 80 percent of the population live in cities. Another aspect of the transition pertains particularly to women's lives. The demographic transition massively changes the condition of women's lives and therefore underpins the changes that take place vis-à-vis women's position in society. In a pre-transition state, women might have had, on average, six live births during their reproductive lifetime. It monopolised their lives. High fertility trapped women within the domestic domain. High fertility also goes with high mortality: although women might have six live births, they also lose a substantial number of them. In the post-transition state, women have two live births on average and they live much longer. Their two children will probably survive, so reproduction and the domestic domain comes to take up a very much smaller proportion of women's lives. One of the indirect consequences of the demographic transition has been that women have had their position transformed.

People don't notice the demographic transition. It occurs over very long periods of time. In the case of England that transition took 200 years to work out. China is a supposedly rapid transition state but, even though China began to go through it in the 1930s or 1940s, its population will still be growing 20-30 years from now. Birth and death rates came down really quite fast, yet the effects of the transition will last for a period of 100 years. Individuals don't really get to witness those sorts of changes, although they are absolutely fundamental to the way in which human beings live.

Fortunately, I live in a society where life expectancy is roughly 75 years; that applies throughout the developed world. It would be salutary if we were to transport ourselves back to circumstances in which a quarter of children might die before their first birthday, life expectancy at birth could be 30 years or less, there were famines and epidemics of various kinds, and women were having six live births each. That was a totally different world to the one in which you and I are lucky enough to live. It was a world in which people could not plan or control their lives. However, as mortality has improved, so us human beings are very considerably more secure in our environment, and have been able to invest in such things as education in a way that would have been almost impossible when life was unpredictable and hazardous.

Why has mortality declined?

Dyson: The reasons why mortality declined in Europe and North America historically undoubtedly had a lot to do with environmental improvements, water supplies, sanitation, housing, clothing, cleanliness and those sorts of fundamental changes. As time went by, our knowledge about disease causation and our medical techniques improved, and these have made contributions as well. The developing world has benefited to a considerable extent from technical advances devised elsewhere, such as immunisation. In some developing country contexts, sub-structural socio-economic processes have played less of a part in reducing mortality than technical inventions that have come from elsewhere.

Can policies affect the demographic transition?

Dyson: It all comes back to this issue of mortality decline. I don't think governments had much to do with the mortality decline in nineteenth-century Europe. However, looking at the developing world today it is clear that, by introducing various health programmes, governments have had a great deal to do with the fact that their populations are living longer. To some extent the same point applies to fertility. Fertility in Western Europe didn't come down because of government programmes. It came down for a variety of reasons, but essentially people during the first half of the twentieth century and the latter part of the nineteenth century decided for themselves that they wanted to control their fertility.

Developing countries were very aware of the fact that if their birth rate stayed high then there was going to be very considerable population growth. Governments, first in Asia and then elsewhere, decided that they wanted to facilitate the reduction in birth rates, so they set up family-planning programmes. Although there is a lot of academic argument about whether family-planning programmes are effective and how much they bring down birth rates, I don't think there is much doubt that they played some role in making birth rates come down faster than they otherwise would have done. Nowadays, in the so-called `developing world' vis-a-vis both mortality and fertility decline, governments have been much more proactive than was the case historically.

This feature was taken from an interview held at the London School of Economics and Political Science on 7 May 2002. Copyright London School of Economics and Political Science.