Overpopulation

 In 2020, the human population of planet earth is 7.8 billion. In 2023, it has reached 8 billion. Of all the species to have ever existed on the planet, none have been quite so successful as humanity. The first human hunter-gatherers who were anatomically just like us first came on the scene about 200,000 years ago. Their numbers were small—a few thousand at first—but Homo sapiens was an energetic creature and over the course of generations increased in numbers and spread around the planet, from the arctic tundra to the tropics, from rain forest to desert, and even crossing the oceans to make their homes on islands as remote from the mainlands as Hawaii. But their numbers remained quite small—between one and five million at the beginning of the Agricultural Revolution, 10,000 BCE.

Agriculture made it possible for human populations to increase exponentially. Hunter-gatherers tend to have small families—no more than one child every three or four years. Farm families, more certain of where their next meal was coming from—tended to have more children. After all, children on a traditional farm could be put to use while still very young and become economic assets to the community while the children of hunter-gatherers are still learning to find food and shelter in the wilderness. By the first century CE, about 200 million humans lived on the planet—about the same population as modern day Nigeria. While there were vast stretches that remained completely or nearly uninhabited, parts of the world were becoming decidedly crowded. Tertullian, an early Christian writer, philosopher, and occasional heretic, made passing reference to the crowded state of things in the Roman Empire.

Since Tertullian’s time, the earth’s population has, in spite of the continued presence of pestilence, famine, war, and earthquake, continued to grow. In fact, in the second and third centuries CE when Tertullian was recommending sexual abstinence for just about everyone, the world’s population was just beginning to take off. Improvements in agriculture, the Industrial Revolution, better sanitation, and a decided lack of abstinence made it possible for the globe’s population to reach one billion sometime around the year 1804. A century later, it had doubled to two billion. Fifty years after that, it had doubled again to four billion. Today, 7.8 billion men, women, and children occupy the planet, all of them hoping for a reasonably comfortable lifestyle. Most of them want children of their own. Some of them want a lot of children.

Almost any discussion of population growth and overpopulation begins with the Reverend Thomas Malthus (1766-1834). Malthus was born into a large, wealthy, and intellectually inclined family in Surrey, England in the midst of the European Enlightenment. In keeping with English tradition, his oldest brother was raised to inherit the family home and estate. His sisters were expected to marry well and have lots of children. Younger brothers, like Malthus, had relatively few choices. Respectable English gentlemen could go to sea. They could become military officers. Or, they could become clergymen in the Church of England.

For intellectually curious gentlemen like Thomas Malthus, the Anglican clergy offered a number of advantages. The work was not especially challenging. Malthus secured an appointment as curate of Oakwood Chapel in Surrey. His responsibilities included reading a weekly sermon to the assembled parishioners of Oakwood Chapel, performing the occasional wedding, baptism, and funeral, and that was about it. The position gave him a living, which meant that he had a place to live, a modest income, and plenty of time to pursue other interests. Malthus used his ample spare time to write.

Though he was a child of the Enlightenment, Malthus had adopted a decidedly pessimistic view of human nature. He was especially skeptical of the Enlightenment notion that people were fundamentally good and could, if given the opportunity, solve most of the problems of life with a proper application of reason and good will.

As a country parson, Malthus was familiar with the hardships experienced by the common folk of the parish. When the rains came in due season and the crops grew well, food was plentiful and cheap. Life was good. Hard work was rewarded with plenty of food. Confident in their continued good fortune, farm families had children. Lots of children. Inevitably, of course, hard times followed. Crops failed. Hunger stalked the once prosperous families, and children, welcomed into the family just a year or two earlier, became unsupportable burdens. Inadequately fed, children were vulnerable to diseases that better fed children might have shrugged off as a minor inconvenience. They suffered. They died. But then the crisis was over. Food was once again plentiful and more children were born and the cycle of plenty followed by hunger started over again.

These observations were at the heart of Malthus’ 1798 publication, An Essay on the Principle of Population. His argument was straightforward. Human populations tend to grow. As long as there is enough food, shelter, and security, women of childbearing years can be expected to have children every two or three years, leading to what Malthus called a geometric population growth. For example, if a small island, say a hundred square miles, were initially populated with ten men and ten women, and if the resources of that island were plentiful, we could expect each of those women to have at least five children over the next twenty years, at which time the original twenty settlers would have grown to a population of seventy. On an island of a hundred square miles, there are still plenty of resources to go around, so the population growth continues into the second generation when the twenty-five daughters of the original ten women give birth to 125 children. Twenty years later—as the first generation of settlers is beginning to pass from the scene—375 children would be born and suddenly, the island which seemed so spacious would begin to seem a bit cramped. Resources would become a bit less plentiful. By the time this generation had borne their children, as inevitably they would, the islanders would come to experience problems unknown to their grandparents—hunger, overcrowding, and competition for resources that would lead to violence and suffering. Eventually, the population would stabilize with just enough food for survival and the population kept in place by regular visitations of famine, epidemic disease, and warfare. Suffering would no longer be an occasional trial but a continual and inescapable affliction.

But, the optimists of Malthus’ day (and our own) might say, people can be inventive. Even in Malthus day, new crops, better plows and means of cultivation were being invented. Traditional means of agriculture were giving way to new methods which allowed the land to produce more food than ever before. Surely, the human dwellers on this small island could find new ways to feed themselves and their growing population. Malthus agreed, but with a dire warning. Food production could be increased, but only incrementally. An acre of land that produced one ton of wheat last year might, with care and hard work, be persuaded to increase its productivity by ten percent a decade—from 2000 pounds (one ton) to 2200 pounds and then, a few decades later, another ten percent to 2420 pounds and more. But, Malthus warned, in this same time, the population has grown exponentially. Each baby girl born grows up to give birth to five or ten children. The increase in food production will never keep up with population growth unless, alas, the numbers are kept in check by famine, disease, and violence.

This, Malthus argued, is not the story of a small island but of humanity. Unless population growth is restrained by hunger, disease, or violence, human populations tend to double every 25 years. He referred to this as exponential population growth. The carrying capacity of the land and sea to support the population grows, at best, arithmetically—by a few uncertain percentage points a year. Thus, the population will always exceed and surpass the ability of the earth to feed and shelter it. People will die. Looking at the population chart above, there seems to be little reason to doubt Malthus.

Overpopulation is not the same things as having a large or even a growing population. Nor is it synonymous with having a high population density. A region, a nation, or a planet, is overpopulated if the population outstrips the carrying capacity of the land and water. Put another way, if a country does not have enough resources to provide everyone with nutritious food, a safe place to live, useful and meaningful work, an appropriate education, and clean water, that country is facing overpopulation.

Singapore is one of the most densely populated countries on earth. With a population of 5,897,743 (as of July 14, 2021) and a land area of 700 square kilometers, Singapore’s population density is high by any standard. But with an average life expectancy of 84 years, and extremely low rates of child and infant mortality, Singapore’s population appears to be healthier and better fed than many countries with far lower population densities (such as the United States). Singapore is wealthy. It plays a crucial role in the world’s economy and generates enough wealth to import the resources Singapore is not able to create on its own.

But some countries are clearly on the verge of disaster.

Beginning in the 1950s, agricultural scientists, most notably Norman Borlaug, began developing and promoting a host of new agricultural technologies, from fertilizer to new varieties of grain, to better water management and supply chain organizations. This Green Revolution made it possible for populations to continue to grow without the constant threat of starvation. Even so, the earth has only so much land available for farming, and continued pollution and population growth threatens much of its agricultural potential.

In the 1960s, the birth control pill and other means of safe birth control became available in most industrialized countries. Women began to have greater control over pregnancies and intentionally reduced their family sizes. People around the world began leaving the countryside—where farming encouraged large families—to find jobs in the cities—where smaller families were easier to manage and support.

Ironically, families are most likely to remain small—with one or two children—if the parents are confident that those children will survive infancy and childhood and grow to adulthood. Such families are more likely to educate their daughters—with the result that marriage and childbearing comes later in life.

If current population trends continue, it is likely that, while the world’s population will continue to expand throughout the 21st century, by the beginning of the 22nd century, population growth will have come to an end. What that world will look like, with ten billion inhabitants all jostling for space, is a different matter altogether.