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Liz, Tony, Emma and Clara, on the road to Kurnool, India, February 2007

It was late afternoon, the sun getting low in a hazy sky, and our car was the only one on a narrow ribbon of asphalt stretching off into the distance, dusty brown fields on either side. Our Indian driver’s response to seeing the line of bandits blocking the road – stringy-muscled, sun-browned men in all manner of well-worn baggy pants and ill-fitting, mismatched shirts, kids in raggedy shorts and T-shirts, even a few women in their saris – was born more out of the last couple of days’ frustrations than out of any ill will. His eyes darkened and narrowed a little, he muttered what may have been the Telugu equivalent of ‘Dammit, not again!’ and then he jammed the accelerator to the floor. Our Indian colleague Uma yelled, ‘Lock your doors!’ Just as we braced for impact, imagining who knows what carnage, the bandits dropped the rope they were stretching across the road, dived every which way to avoid being run over, and with a couple of big bounces we were over the line of rocks they’d placed in our path. One second, we were worried about being robbed; the next, we were feeling a little as if we were the bad guys, with angry, scared faces flying past the car windows, baskets rolling towards the barrow pit, and us leaving it all behind as we sped down the road.

That was the third time we had had a run-in with bandits in two days, which is why our driver was getting fed up with it. The first time he was downright scared, like the rest of us. Travelling with two daughters you’re supposed to be watching out for – Emma was fourteen at the time, and Clara was ten – adds to the anxiety in those kinds of situations, but as a two-career couple, both needing to do the fieldwork our jobs demanded, we had only two basic parental options. One of them, leaving the girls back in California while we were off gallivanting in India for a month, wasn’t something we were prepared to do. So there they were, with us, our Indian host Uma (the same Uma who was trekking up the Himalayas with Liz in the previous chapter) and our driver, the girls watching the adults to figure out the protocol in this foreign land, as the car was brought to a stop by people banging on the windows and shouting something or other in threatening voices. The odds were decidedly unbalanced from our perspective: a bunch of stern-looking fellows demanding money versus our group of two men, two women and two girls; them on their home turf, us strangers in a strange land; and none of us but our driver able to speak the language (even Uma did not speak this region’s language – there are over a hundred languages in India, after all). As this was the first attempt at highway robbery since we had set out from Bangalore, our driver took the negotiation tack, something along the lines of (as was later loosely translated for us) ‘You really don’t want to mess with these foreigners, the cops would be all over you.’ Whatever he said, it seemed to work, a small donation ensued, the brigands backed off, and we continued down the road.

We hadn’t travelled much further, maybe a couple of hours, when once again we saw congestion up ahead, this time caused by a throng of women moving from car to car. Dressed in spotlessly clean saris of dazzling colours – the pinks, yellows and blues a startling contrast to the stark countryside – they were laughing, singing and playing tambourines, the bangles on their arms sparkling in the sun and adding their own chime to the rhythm. As we got closer, though, we sensed that something was a little off. The tambourine players seemed to be intentionally creating a distraction; then a different group of saris would swoop around the car that had been brought to a halt. And all of the sari-wearers’ shoulders seemed a little broader, and their hips a bit narrower, than they ought to be. When we got closer still, we saw that the elegantly made-up faces and sari-clad bodies were in fact those of men. One more thing to explain to our daughters: it was a gang of transgenders (known as ‘hijras’ in India) who were holding us up. Honestly, there’s not much to do in that situation but laugh, part with some money, and go on your way. Even Uma was surprised.

We had landed in Bangalore a few days before, and were journeying from there to some caves we needed to explore in the off-the-beaten-path Kurnool district, about a hundred miles south of Hyderabad. As we set out, our heads were still reeling a little from jet lag and the culture shock that inevitably hits a Westerner on their first trip to India. In Bangalore the sensory chaos was awe-inspiring, at times overpowering: what seemed like infinite numbers of sputtering, belching and roaring motorcycles, yellow tricycle taxis, cars, buses, trucks, bikes and pedestrians, with a few cows thrown in for good measure, jockeying for a space on the road or on the vehicles, no apparent rules, apparently every man and woman for themselves. The tempting fragrances of baking naan and exotic spices somehow found their way through the wood-, coal- and petrol-fumed air. Women completely shrouded in black burqas clustered in front of a shop window displaying sexy red underwear on otherwise naked mannequins. Well-dressed businessmen and fashionable ladies in all sorts of colourful attire milled through elegant shops and high-end restaurants, while beggars conducted their forlorn business right outside. Feral dogs roamed the alleys even in the centre of town. And as we walked down the streets – a mishmash of pavement and dirt – there was ubiquitous chatter, none of it understandable to us, coming from faces that radiated every expression from bright smiles, to curiosity, to in a few cases a touch of hostility.

After that full-on immersion in the human condition, the road trip – highway robbers and all – felt downright relaxing, except for what seemed to us several near misses of head-on collisions, but which our driver assured us were all in a day’s work for him. Even the best roads have few signs, and many are barely wide enough for one vehicle. Passing means finding any wiggle room you can, sometimes pulling in your wing mirrors. As we drove we were barraged by pedestrians, oxen carrying their loads, crammed buses with people hanging out of the windows, sitting on the roofs or holding on to the rear bumpers, and the extraordinary Indian trucks, which are lovingly and beautifully decorated, often with little blinking Christmas-tree lights, tasselled front-window curtains, or hand-painted slogans like ‘India is Great’ in bold blue letters on a bright orange and yellow background.

We finally navigated to the caves, after driving through a village street so narrow that we could touch the walls of the houses on either side if we stuck our hands out of the window – and where surprised faces looked up from washing, cooking, napping and all manner of everyday activities to see the rare sight of a nice car with a family of foreigners basically driving through their living quarters. We were in a little-populated area by Indian standards, but still, there wasn’t a square inch of land that did not have a heavy human footprint. And we had long ago left power and running water behind.

The purpose of our journey was to find some rich fossil deposits in those caves that would tell us something about what India’s wildlife and the rest of the ecosystem were like before the country’s human population grew to its present density – among the highest in the world, with close to 1.3 billion people packed into an area about a third the size of the United States, where only 316 million people live. The part of India we were in was particularly interesting to us in that regard, because humans (or our closely related progenitors) had occupied that landscape for more than a hundred thousand years.

The fossils were there, as was an enormous python Emma revealed in the beam of her flashlight – it probably fed on some of the millions of bats whose eyes shone down from the roof of the cave. But truth be told, we were a lot more concerned with the tens of millions of people we had been seeing all around us. Because we knew that by the time Emma and Clara were our age, the average population density of the whole world’s habitable land will be about equal to India’s now. We wondered, what might we expect to see in a world like that?

Paul Ehrlich presented one vision in his classic book The Population Bomb, published in 1968. Perhaps more than any other single effort, that book brought human population growth into the public consciousness, in no small part because it painted a near-future world that looked like a slum in one of India’s most densely populated cities:

I have understood the population explosion intellectually for a long time. I came to understand it emotionally one stinking hot night in Delhi a few years ago. My wife and daughter and I were returning to our hotel in an ancient taxi. The seats were hopping with fleas. The only functional gear was third. As we crawled through the city, we entered a crowded slum area. The temperature was well over 100, and the air was a haze of dust and smoke. The streets seemed alive with people. People eating, people washing, people sleeping. People visiting, arguing, and screaming. People thrusting their hands through the taxi window, begging. People defecating and urinating. People clinging to buses. People herding animals. People, people, people, people. As we moved slowly through the mob, hand horn squawking, the dust, noise, heat, and cooking fires gave the scene a hellish aspect.

Although Paul (and his wife Anne, a powerhouse of facts, figures and logic also known for her own work on population growth) fully recognised that there is much more to India than that first impression, his point was a simple one: that night in Delhi was what he thought the world could look like if its population continued to grow as it had been doing in the years leading up to 1968. In fact, he thought there was a very real possibility that population growth would drive the world into despair before the year 2000 – let’s call that Ehrlich’s Hell – in large part because of the difficulties in producing adequate food and other resources.

To everyone’s great relief (Paul’s and Anne’s included), Ehrlich’s Hell didn’t happen, at least not globally, and at least not yet, for reasons we’ll talk about towards the end of this chapter. It hasn’t even happened in India – cities like Bangalore are vibrant, thriving places; crowded yes, but exciting and full of opportunity too. The basic point made in The Population Bomb, though, and which Paul and Anne continue to make, remains a fact. There are biological limits for the human species, just as there are for every other species, our incredible technological achievements notwithstanding. And the world is moving towards those limits all too fast.

Here are the sobering realities. After we had colonised all the continents except Antarctica, the prehistoric human population averaged somewhere around ten million. It took thousands of years, until the early twentieth century, to grow to two billion, which is the number of people the Earth is thought capable of supporting without further major technological interventions. With those interventions, our population has almost quadrupled just since our great-grandparents’ time, to more than seven billion of us today. If we humans, averaged worldwide, continue to grow our population at the rate we’ve done over the last decade, our numbers will rise to over twenty-seven billion by the year 2100.

Few, if any, people who make their living studying biology think that can actually happen, as we’ll elaborate upon in later chapters. For one thing, there is not enough land to grow food, or enough fish in the sea, to feed that many people. For another, wars, disease and other catastrophes would almost certainly knock the human population back to significantly smaller numbers long before we hit twenty-seven billion – that is, sometime in the next few decades – as past history is all too clear in showing us. The infamous Black Death of the fourteenth century killed an estimated 30 to 60 per cent of Europe’s population; the one–two punch of the First World War and the 1918 flu pandemic may have wiped out as much as 9 per cent of all the people in the world; and the Second World War felled as much as 4 per cent. Basically, as we tried to keep growing to twenty-seven billion, we’d be packed so tight that we would be like too many rats in too small a cage, and nature’s version of population control would kick in. Ehrlich’s Hell would almost certainly spread far and wide.

What does look inevitable, though, based on just about any reasonable population-growth model out there, is that we’re destined to see a world with somewhere between nine and ten billion people by the year 2050, as we’ll explain in a little more detail below. That virtual certainty means the world you’ll be living in by mid-century is going to be very different from the one you are used to now. The big picture is that we have to pack a couple of billion more people into the relatively small proportion of Earth’s land that is available for occupation. That’s actually only about 20 per cent of the planet’s land surface, which is what’s left over after you subtract the 40 per cent we need to grow food and the 40 per cent that is such inhospitable terrain – rugged mountains, barren deserts, glaciers – that it can’t be heavily populated. The upshot is that if you like rural living, kiss it goodbye; those wide-open spaces peppered by just a few houses will be no more. City life will even more resemble living in a sardine can. As Paul Ehrlich put it: ‘People, people, people, people’.

To set what is going to happen in perspective, just think about current population densities. In 2013 India packed in (on average) about four hundred people per square kilometre, compared to the United Kingdom’s 260, and the United States’s thirty-two. By 2050, on average we’ll see India’s population density everywhere we can easily live. Of course, most people are crammed into cities, where population densities are off the charts compared to averages for a whole country. Greater Los Angeles has 1,400 people per square kilometre, greater Beijing 3,200, greater London 5,600, the New York metropolitan area 10,600, and Delhi twelve thousand. All you have to do is walk down a main street in any one of those cities – or worse yet, try to drive down one of them – to get a sense of what such population densities really mean for a way of life. Yet children growing up now are likely to look back when they are adults, and remember the cities of today as being sparsely populated. The United Nations estimates that by the year 2050, 70 per cent of humans, up from today’s 50 per cent, will be urban dwellers – that is, 6.4 billion city folk versus the present 3.3 billion. Almost double the number of shoulders to jostle you as you try to walk down the pavement.

If you’re from a developed country, as most of you reading this book probably are, and especially if you already live in a city and are pretty happy there, most things you’ve heard about population growth may well make it sound like somebody else’s problem. After all, in developed countries, we like to think we’ve got fertility rates pretty much under control (although that’s actually not the case in the United States, as we’ll see). You probably already know that it’s in poor countries that the population is growing fastest, and sad as it is to hear about deteriorating conditions on the other side of the world, you may think that things aren’t apt to change all that much where you live. But if you reflect a little more deeply on that assumption, you’ll realise you are already experiencing the impacts of population growth.

Here is one example from our own lives. It is a first-world problem, for sure, but it is illustrative in showing how growing numbers of people influence nearly everything. Emma and Clara have grown up a lot since they travelled to India with us. They’ve both finished high school and have gone off to college, but the angst of their college application process is recent enough that it still lingers in our minds. We are not alone there: college application angst infects millions of American households each year. But the elevated stress of that whole process is a new thing, because competition for college slots is just so fierce these days. Back when we were of high-school age, you threw in one or two applications, maybe three if you were really motivated, and you didn’t worry too much, because, assuming you had decent grades and hadn’t done anything too egregious, your chances of getting into where you applied were pretty good, even in top-tier universities. We’ll use Stanford University as an example, simply because we live next door to it and Liz works there. About 22 per cent of 9,800 applicants were admitted in 1970.

Back then, we (and certainly not our parents) never thought to track those percentages (or of applying to Stanford, for that matter). But today, things have changed. High-school students and their parents are well aware that in 2013, only 5.7 per cent of nearly thirty-nine thousand applicants were admitted to Stanford, and in 2014 it was even worse: 5.1 per cent of 42,167 applicants. That’s not confined to top-tier universities; it’s a global trend. In fact, what’s going on with Stanford applications is mild compared to what’s happening at top-level universities in highly populous places like India, which are routinely turning away 98 per cent of their applicants. The Indian Institute of Technology usually receives up to five hundred thousand applications, and accepts only 2 per cent of them; Shri Ram College of Commerce, part of the University of Delhi, has just four hundred slots for twenty-eight thousand applicants – only 1.4 per cent.

Those kinds of numbers are what cause stress levels in American households with high-school-age children to go through the roof each college-application season. Families (at least, the relatively few who can afford it) spend thousands of dollars to increase their children’s SAT and ACT scores by a few points, and then hundreds more dollars for them to apply to a dozen or more colleges, all carefully vetted and sorted into the categories of ‘reach’, ‘target’ and ‘safety’ schools. The reality is that the chances of getting into your top choice are slim at best, and random chance often dictates acceptance even into the safety schools. The net effect is that among high-school students (and their parents not infrequently get in on the act as well), competition can be fierce for grades, recommendations, internships, sporting teams and those other coveted achievements that make a college application stand out.

All this stress goes right back to the fact that there are so many more people in the world nowadays. Despite universities increasing their class sizes to provide places for more students, there just isn’t enough money, available classroom and lab space or land to make it possible for universities to accept much higher percentages of the applicant pool. More people apply each year in part because there are simply more students of college age each year. Over the same time that applications to places like Stanford quadrupled, global population doubled (3.7 billion in 1970, compared to 7.1 billion in 2013). On top of that, proportionately higher numbers of all those new families worldwide moved into socioeconomic categories where a shot at a university education seemed worth taking – that’s a good thing, but it still brings the overall chances of acceptance down. And, in the face of higher odds, more American students apply to multiple colleges to hedge their bets, further increasing the applicant pool for many colleges simultaneously.

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 was in its suburbs, which grew by 8 per cent, whereas the city centre actually lost about 5.8 per cent of its population. This illustrates another point: when cities get too crowded, the only way they can grow is out. Mumbai now packs in more than twenty thousand people per square kilometre over an area of about five thousand square kilometres – equivalent to a square of real estate that measures a little over seventy kilometres on each side. And of course, if they don’t have adequate infrastructure, as is the case with Mumbai and many other cities, living conditions are not very pleasant.

The lesson here is that as population grows, people flock disproportionately to the most desirable places, which, in the absence of equally fast growth of infrastructure, causes some major problems. In Bangalore, for example, the influx of people has outpaced both the infrastructure and the availability of natural resources, making it routine for electricity and water to be available for only parts of the day in those areas of the city that even have access at all. Yet that lack of supply leads to higher prices, so even as the quality of life goes down, the cost of living goes up. In the state in which Bangalore is located, Karnataka, the cost of keeping the lights on, and supplying the population with fuel and food, has more than doubled since 2005. This reflects a general trend in the ten most populous states in India.

The flip side is that if cities do develop adequate infrastructure to handle high population densities, the cost of living goes sky high because of limited supply of homes and office space in the face of high demand, and the costs of maintaining all that infrastructure. Manhattan, for instance, has a population density of 18,500 people per square kilometre, not too far below that of Mumbai. A nice place to live, for sure, if you like city living, but at $3,973 per month, the average apartment there will cost you about $2,800 more per month than the nationwide average for the United States. New York City as a whole, with 10,600 people per square kilometre, is the fifteenth most expensive city in the world. Greater London is even more pricey: with 5,600 people per square kilometre, it was the most expensive city in the world in 2014. Such figures drive home the point that it costs a lot – and to many people, is prohibitively expensive – to live in a city that is both densely populated and has a well-functioning infrastructure, although of course the correlation between population density and cost of living is modified by a host of other factors, such as governmental system, proximity and access to natural resources, town planning, and so on.

The general lesson of rapid growth of a city’s population outstripping its capabilities to provide adequate infrastructure applies worldwide. In China, Beijing provides another cogent example. In the decade 2000–2010, China’s population grew about 6 per cent, reaching a little over 1.3 billion people. In the same decade, Beijing’s population increased 30 per cent, from about fourteen million to twenty million. The difference in percentage-growth is because, just as happened in Bangalore, many, many people migrated from the countryside to the city. As a result, Beijing too is experiencing problems: a water supply that can only support 60 per cent of the city’s residents, inadequate housing and public transportation, lack of access to medical care and education, and air pollution so bad that on many days the only way to see what the sunrise would look like is to look at a stock picture on a big video screen in Tiananmen Square.

As far as nations with growing populations go, India and China are probably the lucky ones, because the end of their population growth is in sight. Given the pace at which birth rates have been decreasing in those countries, both are on track to see growth of their populations stop by mid-century, and then at least remain stable and possibly even decline. And both are large nations that are rapidly advancing their economies, technology and social systems with at least some foresight of population-growth impacts, and with the full awareness of their governments that slowing population growth is a priority.

Not so with many countries that are in much worse shape economically, and with even less adequate natural resources. According to the most recent demographic projections, it seems a fait accompli that by 2050, ‘Five least developed countries – Bangladesh, Ethiopia, the Democratic Republic of the Congo, the United Republic of Tanzania and Uganda – will be among the twenty most populous countries in the world.’ By 2100, three more least developed countries will climb into the top twenty list for most populous – Niger, Sudan and Mozambique.

In fact, it seems to be a general rule that the poorer the people, the faster their population grows. This correlation holds both within countries, and from nation to nation. In India, for instance, birth rates among higher economic classes are pretty much at replacement value; the growth that is still occurring is in the poor rural population. And at the global scale, it is the poorest countries that are the population-growth hotspots. The UN Population Division projects that most of the forty-nine least developed countries are on track to see their populations triple or more between 2013 and 2100, and several are heading for a fivefold increase, including Burundi, Malawi, Mali, Niger, Nigeria, Somalia, Uganda, the United Republic of Tanzania and Zambia. You might have noticed that countries in Africa seem to be showing up with high frequency on these lists, and indeed Africa is the place that promises to launch a tidal wave of global change from its rapidly growing masses.

Which brings us back to the impacts on developed nations. Sudan and South Sudan are regions that provide a window into where the world would be headed if population growth in Africa plays out as predicted. The two countries’ combined populations grew from 8.3 million in 1950 (Sudan 5.7 million; South Sudan 2.6 million), to 45.5 million in 2010 (Sudan 35.6 million; South Sudan 9.9 million), to 58.5 million in early 2014 (Sudan 47.5 million; South Sudan eleven million). That sevenfold increase of numbers of people in the region has been accompanied by a twenty-two-year-long civil war that in 2011 finally split what used to be one country into two; genocide in Darfur that has gone on since 2005 as Janjaweed (the ‘devils on horseback’) militia and Sudanese forces maraud through villages on ethnic-cleansing missions; and widespread hunger, disease and death. These are life-and-death problems for the countries’ inhabitants – in South Sudan alone, in February 2014 a third of the population, nearly four million people, were desperately hungry, nearly a million people had been displaced from their homes, many thousands had been killed, and government forces and rebels were razing towns for what seemed no good reason.

That translates to some very noticeable global impacts. The cost of humanitarian aid to South Sudan quickly rose to over £800 million, and the conflict drew in neighbouring countries, in this case army and rebel fighters from Uganda. At an even larger scale, war-torn, unstable countries become breeding grounds and safe havens for international terrorist groups, which is exactly what happened as far back as the 1990s in the Sudan region, and which continues to be a problem there today.

The link between rapid growth, local wars and escalating global conflict is one of the most important population-growth impacts. We devote Chapter 9 to that topic, but a pertinent issue to mention at this point is that with rapid population growth usually come important changes in the so-called population pyramid. The ‘population pyramid’ refers to the number of people in infant, child-age, teenage, young adult, older adult and geriatric age groups. Rapid population growth bulges the teenage and young adult categories, which means there just get to be too many curious, energetic young people with no productive way to channel their energy. You can see that bulge in recent trouble spots such as Sudan, South Sudan, Egypt, Somalia, Pakistan and Afghanistan, where about 20 per cent of the population is fifteen to twenty-four years of age. In much of Africa, about half the population is aged fifteen or below, and just 3 per cent are sixty-five or older. Contrast that with more stable countries, like the United States, the United Kingdom, France, Germany, Norway or Japan, which have only about 17 per cent of their populations under the age of fifteen, and 16 per cent aged sixty-five or older.

The problem with swelling the ranks of young people relative to the rest of the population, especially in poor countries, is that unemployment increases disproportionately among young people as well. Indeed, unemployment among young people was one of the key drivers that led to the Arab Spring uprising that toppled rulers throughout the Middle East, including Hosni Mubarak’s regime in Egypt in February 2011. The same problem was still causing huge protests that threatened Mubarak’s successor Mohamed Morsi in early 2014, when eight out of every ten jobless Egyptians were under the age of thirty. The projections of the population pyramids for these and other poor countries, even assuming they drop their current higher-than-replacement birth rates to replacement values, suggest that the fifteen-to-twenty-four age category will continue to remain at around 20 per cent of the population well into mid-century. Which means that millions more unemployed, high-energy and highly intelligent young people will be either expressing their dissatisfaction and destabilising society in their own countries, or looking for opportunities elsewhere. The resulting societal volatility in the poor countries with an oversupply of young people is further fuelled by the paucity of experienced, older and wiser leaders.

At the same time, the population pyramid of the richer countries will be turning itself upside down. An inevitable side-effect of slowing population growth rates is going through a period when old people outnumber the young. This is because during baby boom years, as happened in the United States right after World War II, lots of young people are added to the population. If they don’t have babies in equally copious numbers, the older people end up outnumbering the children coming up the ranks behind them, with obvious societal impacts, not least of which is that as the baby boomers grow older, there are fewer and fewer younger relatives to care for them in their old age. In addition, the workforce of people in the young to middle-age categories becomes comparatively small, hampering society’s ability to fund and staff programmes that give senior citizens the level of care and comfort they need. Such impacts can turn society upside down – for example, in Japan, more adult nappies are sold than baby nappies, a consequence of people in the fifteen-to-twenty-four age category making up only about 10 per cent of the demographic, compared to those over sixty-five, who comprise 23 per cent.

Remember, most of these population-growth impacts we’ve pointed out are a best-case scenario, which assumes that fertility rates will, within the next thirty years, fall to replacement value in all countries in which they are not already there. In this book, we’re not even going to try to imagine just how bad things will get if we don’t drop fertility rates to replacement level, fast – except to say, we suspect we’d really get to see what Ehrlich’s Hell looks like. A key point to remember, though, is that no matter which of the population trajectories we actually follow – getting to replacement rate fast, half a child below replacement rate, half a child above replacement rate, or business as usual – we’re still going to hit between nine and ten billion people by 2050. That’s the reality we’re stuck with in trying to make a viable future, and all the other issues we cover in this book are underpinned by it.

The trillion-dollar question, then, is whether it is actually possible for the human population to top out at no more than ten billion by 2050. The answer, fortunately, is a resounding yes. There are three ways to get there. One of them is a way nobody wants – some sort of global catastrophe that wipes out a large portion of the human population. We’ll elaborate on the possibility of this in later chapters – things like pandemics, or war. But the bottom line is that a global catastrophe would be the most tragic sort of population control, filled with pain and loss, dystopia for most of us. There are better ways.

China hit on one solution: the one-child policy, which was officially announced in September 1980 in response to population growth that had been encouraged after a famine cost at least thirty million Chinese lives a generation earlier. The law imposed severe penalties in the form of fines, taxes, or even property loss, for families that exceeded their allotted single child, and rewarded families that stayed below the limit. Two generations later, the success of this approach in terms of limiting population growth is undeniable – China’s population is poised to peak around 2030, after which demographic models indicate that it will fall quickly back at least to the level it was in the 1990s, about a 30 per cent decrease with respect to its peak population size. The social success is arguable. By the standards of most countries, injecting that amount of government control into the bedroom would at best be wildly unpopular, and would be viewed by many as downright draconian. It also introduced some real problems that have to be grappled with now and in the future, among them a disparity in the numbers of young men (too many) versus young women (too few), as a result of a cultural preference for boys which often led to infanticide for girl babies; the abandonment of unwanted children; and ‘Little Emperor Syndrome’, which refers to the fact that a generation of Chinese have grown up in the absence of siblings, with the result that many exhibit poor social skills, feel entitled, and are risk-averse. In addition, China is already experiencing the topsy-turvy population pyramid that other countries will soon be seeing, with simply too many old people to be cared for by the much fewer younger ones.

The third way to bring down birth rates rapidly is the one that has enjoyed the most widespread success, with the main social consequences being positive. It is, in fact, the one that has been employed in most places in the world that are now at or below replacement fertility rate. It’s deceptively simple: make sure girls have access to decent education and job opportunities, and that contraception is readily available to those who want it. Time after time, this approach has resulted not only in bringing fertility rates under control, but in raising the standards of living for families and communities. Education is particularly important: the good things that correlate with educating girls and women not only include many fewer births, but also healthier mothers, better survival of infants and children, decreased risk of sexually transmitted diseases like HIV/AIDS, and much better earning power. The economic rewards alone are big: just one year of primary school tends to add 10 to 20 per cent to a woman’s earning power later in life, and a secondary-school education gives her 15 to 25 per cent more. Which of course also means her family enjoys that much better quality of life. More than that, the country does too. Studies show that by empowering women through education, national economies benefit.

It was just such an approach that turned what is now one of the most densely populated countries in the world away from the brink of disaster. The tiny island nation of Mauritius, located about two thousand kilometres off the eastern coast of Africa, packs in more than six hundred people per square kilometre, a density one-third higher than India and four times higher than China. At about the same time that China was recognising its population-growth problem and instituting its one-child policy, Mauritius was recognising that its ballooning population was straining resources too. The local elimination of malaria, higher living standards and improved health care had brought down death rates, while birth rates continued to increase at a fast pace. Both countries integrated access to contraceptives into their health-care systems, but Mauritius emphasised education instead of laws that limited family size, including making school free by 1976, which made it much easier for families to choose between sending their sons or daughters out to work or continuing their education. But already by that time, as Ramola Ramtohul wrote in an article entitled ‘Fractured Sisterhood: The Historical Evolution of the Women’s Movement in Mauritius’, ‘Mauritius had a generation of young women, especially among the upper classes, who had had access to quality education and thus had a different outlook on life’ (Afrika Zamani 18 & 19:71–101, 2010–2011).

The result: a more than 60 per cent decline in fertility rate over the years 1965 to 1980, and a 75 per cent decline by 2010. Along with this came increasing prosperity for the country’s people as a whole – from a low-income agricultural economy in 1968 to a diversified middle-income economy over the ensuing decades. In fact, for the past few years Mauritius has ranked first among Africa’s countries (and forty-fifth worldwide) in terms of economic competitiveness, a measure that includes such things as infrastructure, education, financial market development, technology and market size.

That recipe for success is translatable to other countries that today stand where Mauritius did half a century ago, but it requires one more essential ingredient: tolerance for diversity of cultural traditions, and openness to new ways of doing things. Mauritians had those things built in through their history, with a succession of Portuguese, Dutch, French and British colonisers, who over the course of a few centuries melded with Africans (originally brought in as slaves), Indians (brought in as indentured servants when the slave trade was abolished) and Chinese settlers. Once colonial rule was removed, the resulting ‘rainbow nation’ included four ethnic and four major religious groups that had found ways to peacefully co-exist and work together to make things better. That kind of tolerance and cooperation will be absolutely essential if the Mauritius success story is to be replicated elsewhere; religious intolerance and ethnic rivalries end up being deal-breakers.

The drop in fertility rates in countries like China, Mauritius, India and others was unforeseen by Paul Ehrlich when he wrote The Population Bomb, and is one reason his prediction of widespread doom by the year 2000 did not come to pass. When he wrote the book, fertility rates in such countries were near six children per woman or higher; less than a decade later, the carrot or stick approach began lowering that precipitously, with the effect that by the year 2000, the average fertility rate in those countries had fallen to 2.5 or fewer children per woman. The lesson there is that it is very possible to bring population growth rates under control fast, especially when it is done with the carrots of education and economic betterment, in ways that make the majority of people happy and more productive.

The other very important thing that The Population Bomb underestimated was human innovation. The prediction of doom was strongly influenced by the food crisis that was looming in 1968 – people in poor countries had been dying of starvation on a massive scale over the previous few years. But with the recognition of world hunger as a problem, innovation and cross-nation cooperation kicked in, taking the form of the Green Revolution, which ramped up food production many times over in just two decades, and thereby staved off mass starvation for a billion or so people. Later, along came computers, the internet and mobile phone technology, which now make possible a global conversation about any world crisis, and harness what could be called a global brain – at last count more than six billion connected people – to formulate and implement feasible solutions. So we bought some time through the last bit of the twentieth century. What about now?

One more lesson comes out of the nearly four decades we’ve had since 1968 to observe how population growth and the human spirit actually work: despite the fact that things didn’t crash by the end of the twentieth century, we are not out of the woods by any means. We now know with reasonable certainty that in just the next half a lifetime, some ten billion people will be on the planet, seething masses overwhelming the capacities of poor countries and banging at the doors of rich ones. As a result, cities will at least double in size, the old will outnumber the young in many communities, and many more places will see their social, political and economic systems put in a pressure cooker. Mind you, this is the best-case scenario – where we rapidly bring fertility rates down to replacement rate in all the nations where that is currently not the case. Even this optimistic scenario means that population growth is about to tip humanity into a future that will be as different from the present as the India we experienced in 2007 was from our home in the United States back then. Whether that future ends up looking like Ehrlich’s Hell remains to be seen – it still could, if we make the wrong choices.

But one thing is for sure: sustaining at least the quality of life that the world provides to people today is not going to happen if we ignore how an extra three billion of us are going to impact the planet. It’s not just our numbers we have to worry about – it’s also what each of us needs and wants.