Ten thousand years of human population growth Source: Adapted from Population Reference Bureau (1984) World Population: Fundamentals of Growth, Population Reference Bureau, Washington, DC
Distribution of biological production among plants and animals in the ecosystem food web
Human Ecology – Basic Concepts for Sustainable Development
by Gerald G. Marten
http://www.gerrymarten.com/human-ecology/chapter03.html
Chapter 3 – Human Population
Human population history
From hunting and gathering to agriculture
The physical and mental abilities of modern humans – and their ecological position in the ecosystem – were formed by several million years of evolution as hunters and gatherers. Humans lived in natural ecosystems that contained many different kinds of plants and animals, only some of them suitable as human food. With their hunting and gathering technology, humans were able to capture only a small part of the ecosystem’s total biological production as food for their own consumption. The carrying capacity for humans was similar to that of other animals, and human populations were no larger than the populations of other animals. Humans probably consumed about 0.1 per cent of the biological production in the ecosystems in which they lived.
This changed after the Agricultural Revolution, which enabled people to create their own small ecosystems for food production. Agriculture in its simplest form first appeared about 12,000 years ago in the Middle East. People encouraged wild plants that they used as food to grow near their dwellings, making food gathering easier. They eventually domesticated some of the plants by selecting individual species with desirable characteristics such as edible parts that were larger or easier to process for consumption. They also domesticated some of the wild animals that they used as food. In this way, people were able to increase the percentage of the ecosystem’s biological production that was available for human consumption, and the carrying capacity for humans increased.
The Agricultural Revolution started in the Middle East because that region had the most plants and animals suitable for domestication. Only a few hundred plants and a few dozen animals among all the species in the world were suitable for domestication, and nearly all of them were domesticated at least 5000 years ago. No major new crop or livestock animal has been domesticated anywhere in the world during the past 5000 years, and none can be expected in the future. Some parts of the world, such as Australia and sub-Saharan Africa, had very few plants or animals suitable for domestication. Agriculture began in those areas only after domesticated plants and animals were brought from other places.
Why did humans wait so long to develop agriculture? The effort that people must expend to form and maintain agricultural ecosystems – preparing the land, planting a crop, caring for the crop, and protecting it from weeds, insects and other animals that want to consume it – requires much more human labour than hunting and gathering. People were probably content to live without agriculture as long as they did not need it. It was convenient to have nature do the work of producing food. However, inhabitants of the Middle East may have felt a strong need to find new ways to procure more food about 12,000 years ago, when rapid change to a drier climate reduced the biological production and human carrying capacity of the Middle Eastern ecosystem.
Over a period of several thousand years agriculture spread through the Middle East to Asia, North Africa and Europe, and arose independently in China, North America, Meso-America, South America and New Guinea. Human populations increased in the areas with agriculture. New improvements in food production happened in different places at different times, so the human carrying capacity at any one place increased in steps. Any significant new improvement in agricultural technology generated a rapid increase in carrying capacity, and the human population of that region increased to the new carrying capacity over a period of centuries. Once population growth was no longer possible, people felt the stress of limited food supply. This stress, known as population pressure, motivated people to develop additional improvements in agricultural technology, or adopt more productive agricultural practices from neighbouring people. This made the carrying capacity higher, and the upward cycle of human population continued as a positive feedback loop between population and technology.
The progressive increases in agricultural production generally required more effort to structure ecosystems so that a larger share of their biological production was channelled to human consumption. This is the principle of ‘no free lunch’. Every choice has advantages and disadvantages. Every gain has its costs. One of the costs of more food is more work.
The human population of the planet increased gradually for more than 10,000 years after the Agricultural Revolution. The largest populations were in the great river valleys of India and China. There was a substantial increase in Middle Eastern and European populations during this period. The world population declined by 25 per cent when the plague known as the Black Death swept across Asia and Europe during the 14th century, but it quickly returned to its former numbers during the following century. People in Europe were feeling the stress of a population at the limits of its carrying capacity, but the situation changed as the more powerful European nations embarked on worldwide colonialism and trade during the 16th century. The supply of resources increased Europe’s carrying capacity, and the European population began to grow. Carrying capacity increased even further as the Industrial Revolution gained momentum during the 18th century.
The Industrial Revolution
The Industrial Revolution had a major impact on agriculture. Highly productive crops such as wheat, corn, potatoes, sweet potatoes and rice, which were previously restricted to particular regions of the world where they originated, were quickly spread around the world by European trade and colonialism, giving farmers an expanded ‘menu’ of highly productive crops from which to choose. Mechanization gave farmers the ability to structure ecosystems more than had been possible with only human and animal labour. The Industrial Revolution was accompanied by a scientific revolution, as well as new agricultural technologies that increased agricultural production even further. People were able to capture a much larger percentage of the ecosystem’s biological production for their consumption, and carrying capacity increased. The increase in carrying capacity since the Industrial Revolution has been so large and so continuous that the planet’s human population has been able to grow exponentially for the past 250 years.
Birth rates were high before the Industrial Revolution. Large families helped to meet the high labour demands of farm life and ensure the survival of children in order to care for parents in their old age. Improvements in public health from the scientific revolution drastically reduced death rates in industrializing countries. Their populations increased rapidly because birth rates remained high. By the 19th century, urbanization and improved survival of children made large families less necessary. Birth rates started to decline as people adopted various methods of limiting family size. The populations of industrialized nations continued to grow rapidly through the 19th and most of the 20th centuries. However, their internally generated population growth was nearly zero by the end of the 20th century. The populations of some industrialized nations continue to grow primarily due to migration from other countries.
Increase in the populations of industrialized and developing world nations from 1800 to 2000 Source: Data from Population Reference Bureau, Washington, DC 1900 Developing world Industrialized nations
Population ‘ageing’ has recently become a major issue in industrialized nations. There is a change from a rapidly growing population with a high percentage of young people to a population that is growing slowly or not at all with a high percentage of older people. This is reducing the number of economically productive young people compared to older retired people that they must support. ‘Ageing’ is well underway in Japan, it is beginning in Europe and North America, and within a few decades it will become a major issue in developing world countries that reduce their population growth. Some people in countries with an ‘ageing’ population have suggested that birth rates should be increased to provide more young people to support the elderly – a course of action whose short-term benefits would exacerbate the long-term overpopulation problem, resulting in more elderly people to support in the future. Many industrialized nations such as Japan already have populations and levels of consumption that are much greater than they can support with resources from within their own boundaries. They are scarcely aware of the extent to which they have exceeded their carrying capacity because their privileged economic position allows them to draw upon extensive resources from beyond their boundaries.
Developing world populations began to grow rapidly during the 20th century, when modern public health reduced deaths but births remained high. Most of the world’s population growth is now in the developing world. Large numbers are migrating from crowded parts of the developing world to seek better economic opportunities in North America, Europe and Australia. Births began to decline in some parts of the developing world about 20 years ago, but births remain high in many areas. Even if births decline drastically, the developing world population will continue to increase for several generations. Developing world populations have such a large percentage of young people that, even with smaller families, the number of births from the large number of people of reproductive age will greatly exceed the small number of elderly people who die.
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孔子 (551–479 BC)、釈迦 (563–483 BC)、ソクラテス (469–399 BC) などが生きていた頃の世界の人口は、今の日本の人口とほぼ同じ。人口10万人以下の中小の地方都市も、当時であれば大都市ということになる。
それにしても、最近の人口増加は、恐ろしい。