In 1,000 years, the human race has multiplied 20-fold. Today’s 6 billion people may be 9 billion by 2050. Yet the increase has slowed; rich nations breed less

WHEN Thomas Malthus, an English economist, in 1798 published his “Essay on the Principle of Population” , quoted above, he caused a sensation. At the time the world’s population was close to 1 billion, having risen slowly and erratically from maybe 300m at the start of the millennium; which in turn was probably not much, if at all, more than it had been in 1AD. And today? Give or take the odd 100m of us, 6 billion.

When Malthus wrote, there was no widespread sense that numbers were running out of control. The general mood was upbeat. Indeed, most thinkers considered a growing population a good thing: more people, more hands at work, more output.

A century earlier, a pioneer statistician, Gregory King, had predicted that the human race would double from its then total of around 650m in about 600 years’ time, and ventured boldly:

In fact it will do so in about 2006.

By Malthus’s time, a few prophets of doom had begun to give forth. Giammaria Ortes, an Italian economist, wrote in 1790 that no one wanted to see humanity grow

But Malthus’s message was much more urgent than that. Some—probably unrepresentative—American figures gathered by Benjamin Franklin had persuaded him that, unless checked, most populations were likely to double every 25 years, increasing at a geometric rate (1,2,4,8,16 and so on), while food supplies would grow at only an arithmetic rate (1,2,3,4,5 and so on). Sooner or later the food was bound to run out.

Mankind had a choice: either let matters take their course, thus inviting “positive” checks—wars, plagues and famines—to reduce numbers to sustainable levels; or adopt “preventative” checks to ensure fewer children, for example by bridling passion and delaying marriage. Malthus was not optimistic that enough people would choose restraint. He himself tried to set an example by not marrying until he was 38 (and then had three children in quick succession).

Malthus was wrong in expecting populations to double every 25 years. But not far wrong: in the 200 years since he wrote, the time it takes mankind to double has shrunk from several centuries to 40 years. And he was clearly right to note that the earth’s resources are finite, though he vastly underestimated man’s ingenuity in utilising them more efficiently, and at making new inventions. Technology and innovation, speeded up by the industrial revolution, allowed food supplies to increase at a faster-than-arithmetical rate. Even during Malthus’s lifetime, crop land was being expanded rapidly as forests were felled, and innovations such as crop rotation and selective breeding brought large increases in yields. These continue, through the “green revolution” of the 1950s to today’s high-yielding, if unloved, genetically engineered crops.

What Malthus could not have predicted, since nothing like it had ever happened before and it was barely under way by his day, was something known now as the “demographic transition”: the way societies alter as they get richer. First comes a decline in mortality, leading to a short population explosion; then, after an interval of variable length, a steep decline in the birth rate, which slows, halts or may even reverse the rise in numbers.

For most of human history, people had lots of children, of whom many died in infancy. If things were going well, and there were no serious wars, epidemics or famines, more would be born, more would survive longer, and populations would rise. From about 1000 to 1300, Europe enjoyed a spurt of economic growth. A lot of new land was taken into cultivation, and the number of cities multiplied. The population doubled or trebled.

Enter, in 1347, via the Mediterranean, the Black Death. Within a few years this plague had traversed the continent. By 1400 Europe’s population had shrunk by maybe 25m, about one-third. Plague reappeared periodically over the next three centuries, the last big wave rolling over north-western Europe in the later 17th century, soon after the Thirty Years War, which had already slashed Germany’s population. In the New World, smallpox brought by Spanish conquistadors and European settlers in the 16th century killed maybe 10m-20m of the native populations. Not even the 20th century has escaped such scourges: the worldwide flu of 1918-19 is thought to have caused 25m-40m deaths, far more than the first world war; and since 1980 AIDS has killed some 12m people, so far.

In pre-industrial Europe, frequent food crises also served as periodic population checks. When bad harvests pushed up the cost of grain, more people died and, while the trouble lasted, couples had fewer children. Figures from Tuscany (not alone) in the 16th-18th centuries show grain prices and mortality closely correlated. But by the 19th century the days of famine in Europe were largely over, except in Ireland, where the potato blight of 1846-47 and its side-effects may have killed a sixth of the 8m-odd people.

The transition begins

By the mid-19th century most of Europe was in the first stage of the demographic transition. Mortality had lessened, as wars, famines and epidemics had; local food shortages were rarer, thanks to better economic organisation and transport; public health, medical care (notably, midwifery) and the control of infectious diseases such as cholera and smallpox had improved. The population spurted, as Malthus had predicted. Between 1800 and 1900 Europe’s population doubled, to over 400m, whereas that of Asia, further behind in the demographic transition, increased by less than 50%, to about 950m.

Europe by now was crowded, and most worthwhile land already under the plough. But there was space elsewhere. Thanks to a steady trickle of migration over the previous three centuries, North and South America by 1800 each held about 4m people of European extraction. From around 1850 that trickle became a flood. Over the next 100 years or so, some 50m Europeans quit their continent, most going to North America, others to South America and the Antipodes. At the peak of this wave of emigration, Europe was exporting about a third of the natural increase in its population.

But something else was happening there that would have taken Malthus by surprise: as people came to expect to live longer, and better, they started to have fewer children. They realised they no longer needed several babies just to ensure that two or three would survive. And as they moved from country to town, they also found that children were no longer an economic asset that could be set to work at an early age, but a liability to be fed, housed and (some of them) educated, for years. Worse, with too many children, a mother would find it hard to take and keep a job, to add to the family income. Nor were offspring any longer a guarantee against a destitute old age: in the new industrial society, they were likelier to go their own way.

Thanks to Europe’s new-found restraint, in the past 100 years or so its population has risen only 80%, to 730m, and most countries’ birth rate is now so low that numbers are static or falling. But their composition is very different from the past: better living standards, health and health care are multiplying old heads, even as the number of young ones shrinks.

In contrast, Asia’s population over the same time has nearly quadrupled, to more than 3.6 billion. North America’s too has grown almost as fast, but largely thanks to immigration. Africa’s has multiplied 5 1/2 times, and Latin America’s nearly sevenfold.

Why these differences? From around 1950, mortality in developing countries also began to fall, and much faster than it ever had in Europe. The know-how needed to avoid premature death, especially of small children, travelled so readily that life expectancy in many poor countries is now not far behind the rich world’s. But the attitudes and values that persuade people to have fewer children are taking longer to adjust.

Yet adjust they do. In China, the world’s most populous country, with over 1.2 billion people, and still relatively poor, the demographic transition is already almost complete; not only has mortality come down faster than in other countries with similar income levels, but in recent decades a sometimes brutal population policy (now being relaxed a little) has restricted couples to one or two children. India’s population rushed ahead for longer, and has just reached 1 billion, despite attempts to slow it, including a period in the 1970s when the government promoted large-scale sterilisation. The UN’s “medium-variant” forecast is that by 2050 India’s headcount may be over 1.5 billion, slightly ahead of China’s. Yet in India too fertility has fallen fast. Only in Africa is population growth still rampant, though slowed by AIDS, which in some countries is killing a large proportion of the young adults.

Does more mean worse?

Demographers like to dramatise this recent population growth by asking a spooky question. Of all the people who have ever lived, how many are alive today? The answer requires a lot of guesswork, except for the very recent past; but a fair estimate for the number of people born throughout human history is 80 billion-100 billion. With mankind now numbering 6 billion, the astonishing answer must be: 6-7%. The figures are even more spectacular if you count man-years lived rather than people, because life for early man was usually short: at birth, he could expect 20 years of it in 10000BC, only 27 as late as 1750AD, and 58 today. On that reckoning, those alive today account for one-sixth of the time that humans collectively have spent on earth.

Is all this rise in numbers necessarily a bad thing? Economists have disputed endlessly: does it promote economic growth, by expanding the workforce, or, if it happens too quickly, choke growth off? Their answers seem to boil down to an unhelpful “It all depends.” But then governments’ population policies are not guided solely by economics. Prussia’s Frederick the Great made a sharp political point when he observed in the 18th century that “a country’s wealth is the number of its men.” Two centuries later, Mao Zedong insisted that “China’s vast population should be viewed as a positive asset.”

Of course, numbers are not the only measure. The United States, with its 275m people, has less than 5% of the planet’s population, yet it dominates the other 95%. Still, in many rich countries the birth rate has now fallen so low that the population is actually shrinking; and in some their governments see this as a problem. Their main fear may be that soon there will be too few young workers around to pay for older ones’ pensions. But at the back of their minds there may also be the thought that, say, a Japan of 105m people in 2050 (the UN’s medium forecast) might carry less clout than today’s Japan of 125m.

Mankind had a choice: either let matters take their course, thus inviting “positive” checks—wars, plagues and famines—to reduce numbers to sustainable levels; or adopt “preventative” checks to ensure fewer children, for example by bridling passion and delaying marriage. Malthus was not optimistic that enough people would choose restraint. He himself tried to set an example by not marrying until he was 38 (and then had three children in quick succession). Mankind had a choice: either let matters take their course, thus inviting “positive” checks—wars, plagues and famines—to reduce numbers to sustainable levels; or adopt “preventative” checks to ensure fewer children, for example by bridling passion and delaying marriage. Malthus was not optimistic that enough people would choose restraint. He himself tried to set an example by not marrying until he was 38 (and then had three children in quick succession). Many say the globe is already overcrowded, risking environmental disasters such as global warming and pervasive pollution. Nonsense, say others: with careful management it could carry plenty more, say 10 billion. A few optimists, if that’s the word, muse that, with a bit of squeezing and the astute use of technology, the figure might be several times that, maybe even 100 billion.

One thing is sure: even if from tomorrow every couple on earth practised Malthusian restraint and stopped at two children, the momentum built up by the huge population growth in developing countries since 1950 will keep numbers rising fast for decades to come; the UN’s medium forecast for 2050 is 8.9 billion people. But, fingers crossed, soon thereafter even the poorest countries may have lost their enthusiasm for large families, while couples in some richer countries may—may—have rediscovered that two children are, and have, more fun than one. A century or so from now, if mankind survives that long, its number may have reached a new (and surely better) steady state.