Our point: intense competition for limited resources is the ubiquitous effect of population growth. Of course, supply-and-demand problems are not confined to higher education – we used that example to illustrate that even in areas where you don’t normally think about the problems of population growth, it looms large. There are plenty of other examples of how increasing demand for limited space or goods has begun to change things in your own lifetime, especially if you have lived for a few decades. The traffic is worse. Housing prices have gone up. It is harder to find a job. The list goes on and on.
All of these things you may view as pretty subtle impacts of population growth, but one impact that is not subtle at all is immigration. It’s in the news all the time these days, in country after country. Worldwide, at least every thirty-two seconds a migrant crosses some border between nations, and that’s only the ones we know about. Immigration is where population growth in those poor places that you may regard as someone else’s problem really hits home. More migrant workers are coming in, taking jobs and requiring basic social services that somebody has to pay for. Throngs of people are bowing to Mecca each evening outside Catholic churches in Italy and France. Children are streaming across the Mexican–American border each night, despite expensive fences and patrols attempting to keep them out. Those things are happening because in poor parts of the world, where population is growing fastest, the growth outstrips local resources, and little vignettes of Ehrlich’s Hell emerge. Poverty, disease and death become the definition of normal in those places, and not surprisingly, the people suffering living there want to escape to new territory that offers a better way of life. So they come to your town.
The population is growing so fast in poor countries for what is actually a positive reason – death rates have been coming down. Population growth is a function of both the number of births and the number of deaths. If the numbers balance, the population remains constant; if there are more births than deaths, the population grows; and with more deaths than births, it declines. From the purely biological perspective, in order to keep your species going, you need to have at least two children per family to replace the parents when they die; most species hedge their bets by having a few more than two offspring per set of parents, and humans up to now have been no different. In historically poor places like India, Nigeria and Pakistan, to name just a few, until very recently living conditions were so bad that the only way for a family to be sure to have at least a few children reach adulthood was to have a lot of them. The very good news for many of those places is that they are now gaining access to basic levels of health care and more reliable food supplies, with the wonderful result of reduced childhood mortality; more children have been growing up to have families of their own. For instance, in India, mortality of children under five years old has fallen from about 120 deaths per thousand births in 1990, to about seventy deaths per thousand births in 2010.
But old lessons die hard. Even though survival rates in such places are now higher than they used to be, the ingrained cultural tradition is still to have lots of kids, because people still expect to lose many. Since more children are surviving to have their own babies, population growth rates skyrocket. This lag-time effect means that half of all the population growth between now and 2100 is expected to take place in only eight countries, seven of which are regarded as poor by developed-nation standards: Nigeria, India, the United Republic of Tanzania, the Democratic Republic of the Congo, Niger, Uganda and Ethiopia (listed in order of their contribution to world population growth). In the number-eight spot for countries contributing most to population growth is one that is not poor by any stretch of the imagination: the United States.
These, and other countries like them, now have fertility rates that are too high, that is above two. The ‘fertility rate’ is basically the average number of children born per woman; two is the magic number if you want the population to level off rather than continue to grow indefinitely, because at that number each set of two parents on average replace themselves with two kids; hence a fertility rate of near two is called the ‘replacement value’. To be precise, the actual replacement rate is a little higher than two, presently 2.1 in industrialised countries and 2.3 on a worldwide average, because not all children survive to reproduce, but we round it to two for ease of discussion.
Given current demographics, if all of the countries that now have fertility rates above replacement (like those eight listed above) see a decrease that quickly brings them down to replacement, by 2050 we’d end up with a global population that stabilised at a little over ten billion people, and then remained constant after that. Just half a child over replacement rate, and we’re at more than sixteen billion by 2100. Half a child under replacement rate would allow us to stabilise at around our present seven billion by 2100 – but even in that optimistic scenario we still hit nearly ten billion around the year 2050, before population finally begins to fall. So any way you cut it, we’re adding close to three billion people to the planet over the next three decades. If you are interested in what goes into these models, and country-by-country data, the information is readily available from the 2013 United Nations Department of Economic and Social Affairs Population Division publication World Population Prospects: The 2012 Revision, Highlights and Advance Tables, and Volume II, Demographic Profiles, which provide most of the population numbers we use in this book.
Obviously, the population-growth impacts in poor countries, where the numbers of people are increasing very, very fast, are going to be different from the first-world impacts we’ve been talking about for developed countries. Today poor places – like India, Pakistan and especially many African countries – already find it hard to provide adequate food, water and health care, and basic services like electricity, toilets and sewage-treatment plants, and these problems will only get worse.
Take the best-case scenario of one of these growing-population countries, India. India is on track to decrease its birth rate to the replacement level of around two children per couple by 2050. Even so, between now and then births will add four hundred million people to the country, increasing its native-born population from the present 1.2 billion to about 1.7 billion. This is roughly double the number of people India added from 2000 to 2010, which contributed to dramatic changes in the country. Those changes are hard to miss. In 2012, on a return trip to Bangalore, it was obvious that the city had extended its urban sprawl radically compared to how it was when we visited in 2007. Where there had been open ground, new neighbourhoods, businesses and highways had sprouted. So had the number of shanty towns. Vehicles of every kind filled the streets, and people were ubiquitous, day and night. Seemingly everywhere you looked there was scaffolding made from bamboo-like tree branches, with barefoot workers hoisting buckets by rope, building supersized components of new concrete structures that were transforming the skyline. This, remember, in what is already the most densely populated large country in the world.
That was the on-the-ground expression of some rather startling statistics – while overall India’s population increased by about 17 per cent from 2001 to 2011, Bangalore’s population grew by a whopping 47 per cent. Even its urban sprawl, which tripled the area covered by the city (from 226 square kilometres in 1991 to 716 square kilometres in 2010), has not been enough to prevent a huge increase in population density in the last decade (from 2,985 people per square kilometre to 4,378 in 2010).
This trend to urbanisation as population grows is because people born into poor rural areas tend to move to the city in search of a better life, a pattern that repeats over and over in history, and which, as we noted above, the United Nations predicts increasingly for the future. In India, Bangalore is a particularly good city to come to if you’re looking for work: it is one of the country’s intellectual, economic and entrepreneurial engines. But not all cities experience equal immigration and growth as population increases. Delhi’s growth (21 per cent) was just a little over India’s as a whole (17 per cent) for the period 2001–2011. At the same time the area around Mumbai saw its population increase by only 4 per cent; however, all of that increase