by Dale Easley
16 July, 2003
How many humans can Earth support? Human population was relatively low for most of the hundreds of thousands of years since the first humans evolved. Through the Middle Ages in Europe, plagues would periodically kill off massive numbers of people. Famine was common. Many children never made it to adulthood, and women commonly died during childbirth. There was no understanding of diseases and how they spread. However, the birth of modern science slowed the death rate through three main factors: improved agricultural techniques, better public health measures, and new sources of energy. The two main factors that slow the birth rate, rising standards of living and education of women, have been slower in their effect, still absent in many parts of the world, and less widely distributed. The slowing death rate without a corresponding slowing birth rate has led to a boom in human population.
A strong agricultural base is crucial to any society. In the U.S., only about 3-4% of the population raises the food to feed us all. This frees up the rest of the population for research, public service, education, engineering, medicine, law, etc. The resulting technology, legal and cultural system, and consumer services and products add great wealth to the society, in turn leading to greater investment in education, technology, etc. This pattern can be seen in the rise of ancient civilizations, where large-scale agriculture required cooperation for irrigation, harvesting, and marketing. As society made the transition from hunting and gathering to agriculture, people settled in towns and then cities. The systems of interaction became more complex and were codified into laws. However, as transportation and cities grew, the opportunity for the spread of disease also greatly increased.
Worldwide, the leading killer of children under 5 years old is diarrhea. This is largely due to drinking contaminated water. An estimated 80% of disease in the developing world is due to water-borne disease. These deaths have been virtually eliminated in the developed world, along with smallpox, plague, and most of the other communicable diseases. The development of medicine had two great steps: the recognition of disease-causing microorganisms and the creation of public-health measures to protect society from a polluted environment. Modern medicine has overcome so many diseases that now Americans largely kill themselves through smoking, overeating, accidents, and preventable diseases.
The final step in enabling a huge population increase was the development of fossil fuels (oil, gas, and coal) as energy sources. A major advantage of using a tractor to plow your corn instead of mules is that you don't have to feed a fourth of the corn to the tractor. A tractor is simply far more efficient, but only because there is an available concentrated energy source. These energy sources have enabled us to build skyscrapers and to live in places in the world that are not friendly to large groups of humans—deserts where water must be brought in, fault zones where building must be earthquake resistant, and coastal areas where hurricanes pound the levees we've constructed. There are few places left where humans haven't ventured, built a building, and transformed the environment. Fossil fuels have powered the human expansion.
Can this population growth be sustained? The short answer is no. Soils form very slowly and are essentially non-renewable—once they wash away or are ruined by poor agricultural practices, it may takes decades or more for the land to be useful again for agriculture. Public health in the developed world may be reaching its limits—how far do we want to go in forcing people to do things that are good for them? And fossil fuels will eventually be exhausted. However, there are many people who believe that human ingenuity will rise to the occasion, developing better crops, new sources of energy with less pollution, and healthier ways of living that are still desirable. I hope they are right, though there is and will be a cost—loss in wilderness, endangered species, and open space. Regardless of the future developments, choosing to educate women and share the wealth with the poor makes good political and moral sense, and a byproduct is the slowing of population growth.