Some historians have estimated that in 10,000 BCE, the world population was 2.4 million. By 1,000 CE, it was 295 million. By 1800, it was 900 million. So, for thousands of years, the human population grew, but very slowly. The annual growth rate was probably never more than .5%.
But after 1800, the annual growth rate increased to .8% in 1900 and to 2.2% in 1962, which was the highest rate of growth in human history. After 1962, population has grown, but at a declining rate. Population has grown from 1.5 billion in 1900 to 6.1 billion in 2000, and then to 7.5 billion at the end of 2016.
Growth in population depends on the combination of two factors--the rate of fertility and the rate of mortality. Prior to 1800, the rate of fertility was often high, but the rate of mortality was also high. Women gave birth to many children with the expectation that only a few would survive to adulthood. In the 19th century, beginning in northwestern Europe and North America, fertility remained high, but mortality declined, because improved standards of health and sanitation based on improved knowledge in medical science and public health lowered the rate of infant mortality and lengthened life expectancy. Consequently, population began to grow faster than ever before in human history. No country in the world today has a lower life expectancy than the countries with the highest life expectancies in 1800.
Beginning in the first half of the 20th century, the most developed nations began to show a drop in the rate of fertility. Social scientists have called this the "demographic transition." In the more developed countries, women delay the age of their first pregnancy, and they choose to have fewer children. As parents invest more in the education of their children, and as women have more opportunities for investing in their careers outside the home, parents choose to have fewer children. By the 1960s, some countries saw fertility rates fall below replacement levels (less than 2.1 children per woman), which brought a decline in population along with an ageing of the population. (See my previous post on the demographic transition.)
In recent years, however, there has been some evidence that as societies move into the very highest levels of human development--as measured by long life expectancy, great wealth, and high levels of education--the declining trend in fertility is being reversed. By 2005, Sweden and some other highly developed societies were showing this, although the increase in fertility was still not yet up to replacement levels. (See Mikko Myrskyla et al., "Advances in Development Reverse Fertility Declines," Nature 460 [6 August 2009]: 741-43.) For me, this shows that the natural human desire for children will always assert itself, although parents in the socioeconomic circumstances of modern liberal societies will often prefer to invest heavily in fewer children.
Even if the demographic transition has slowed the rate of growth in world population, the stupendous growth in population has continued. Is this a sign of human progress or not? Many thinkers of the Liberal Enlightenment have said yes. David Hume, for example, in his long essay on "Of the Populouness of Ancient Nations," criticized ancient nations for having a lower growth in population than modern nations, and he argued: "every wise, just, and mild government, by rendering the condition of its subjects easy and secure, will always abound most in people, as well as in commodities and riches. . . . if every thing else be equal, it seems natural to expect, that, wherever there are most happiness and virtue, and the wisest institutions, there will also be most people" (Essays, Liberty Fund, p. 382). Hume believed that population was growing faster in modern nations than in ancient nations because there was more liberty in modern nations: "human nature, in general, really enjoys more liberty at present, in the most arbitrary government of Europe, than it ever did during the most flourishing period of ancient times" (383). After all, the primary difference between the economic life of the ancients and that of the moderns was the practice of slavery among the ancients.
Like Hume, Etienne Damilaville, in his article on "Population" in the French Encyclopedia, edited by Diderot and d'Alembert, claimed that liberty fosters a growing population, because "it is under mild, limited governments, where the rights of humanity are respected, that men will become numerous" (Encyclopedic Liberty, Liberty Fund, p. 502).
This belief that growing population was a sign of human progress in a free society was challenged by Thomas Malthus in his Essay on the Principle of Population (1798), who warned that since population tends to increase faster than the production of food, restricting the number of births was the only way to avoid famine and starvation.
This Malthusian pessimism has been adopted by many modern environmentalists, who insist that the modern growth in human population is unsustainable and must soon lead to a catastrophic collapse of human civilization. In 1968, Paul Ehrich began his best-selling book The Population Bomb by declaring:
"The battle to feed all of humanity is over. In the 1970's the world will undergo famines--hundreds of millions of people are going to starve to death in spite of any crash programs embarked upon now. At this late date nothing can prevent a substantial increase in the world death rate. . . . We must have population control at home, hopefully through a system of incentives and penalties, but by compulsion if voluntary methods fail. . . . The birth rate must be brought into balance with the death rate or mankind will breed itself into oblivion" (11).Ehrlich wrote that he first knew "the feel of overpopulation" during "one stinking hot night in Delhi":
"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 f100, and the air was a haze of dusty 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 slowing through the mob, hand horn squawking, the dust, noise, heat, and cooking fires gave the scene a hellish aspect" (15).For an environmentalist like Ehrlich, Hell is "people, people, people, people"--too many people!
Ehrlich's prediction of massive famines in the 1970s in overpopulated countries like India proved false because of people like Norman Borlaug. Borlaug, an agronomist from Iowa, spent his life developing high-yield hybrid crops that would solve the problem of global hunger. His success in doing this was called the Green Revolution. After working for many years helping farmers in Mexico, Borlaug moved in 1963 to India and Pakistan, where he showed farmers that they could have better crops with bigger yields. He also advised governments that farmers should be paid market prices for their crops instead of imposing price controls to subsidize food for urban people, because such price controls would reduce the supply of food. Today, India and Pakistan produce seven times more wheat than they did before Borlaug arrived. In 1970, Borlaug won the Nobel Peace Prize for his work increasing the global food supply and thus averting the famines predicted by Ehrlich in 1968.
Major famines have largely disappeared from the world. The great famines of the 20th century were mostly man-made in illiberal regimes like the Soviet Union, China, Cambodia, Ethiopia, and North Korea. In the 21st century, socialist regimes like that in Venezuela continue to produce food shortages. Mao's "Great Leap Forward" famine in China (1958-1962) killed 30 million people, making it perhaps the greatest single catastrophe in human history. Once the collectivized farms in China were abolished, and farming was privatized, food production increased, and now China produces a surplus of food for world markets. The freedom for people to choose their own work, and to reap the rewards, has made this most populous nation on Earth prosperous.
For Julian Simon, an economist at the University of Maryland, people like the Chinese farmers and Norman Borlaug illustrate the point that a growing human population is good, because people are so productive and inventive in solving problems that human beings are the "ultimate resource," and so having lots of them is good for us. Simon's classical liberal approach to population made him Ehrlich's greatest adversary.
Simon argued that there are no resources for human life without the human effort to discover and use them. So, for example, petroleum is not inherently a resource. The Native Americans had no use for it. It became useful only after human beings discovered how it could be used to satisfy human desires and then found efficient ways to extract it and sell it.
Of course, human beings are consumers of resources as well as producers, and people like Ehrlich assume that in general people consume more than they produce, so that population growth is bad. But Simon argued that growing human populations in free societies, where people are free to be inventively productive, will produce net increases in resources.