Lester R. Brown, in the first section of the book In the Human Interest, (1974) sums up the history of the human population problem in the framework of four demographic eras. Here is a further elaboration of this theme to serve as a historical backdrop for our demographic situation.

The first era that characterized our civilization was the hunting and gathering way of life. We do not find hunting and gathering in its original form anywhere on earth today. Even those civilizations today, which are very close to the original form of this civilization use some agriculture and/or animal husbandry to obtain additional sources of food. Among these the !Kung people living in southern Africa may be the closest to the original form of this culture. Nonetheless, in the first demographic era of hunters and gatherers the base population was rather small. The extended families formed bands where the hunting was mostly male occupation, while gathering was mostly the work of women and children. In other words, all members of the band, except the very young, were both producer and consumer. The human population was in a demographic balance where death rate and birthrate, both very high, evened off with a bit of positive edge on survival. The hunting and gathering way of life required a very large area per person for survival. As the numbers of the human population slowly increased, there may have been a crisis because of the very large area/person ratio. (Note: According to an analysis of multiple carbon-dated sites conducted in 1984 by James I. Mead and David J. Meltzer, 75 percent of the larger animals (those of more than 40 kilograms live weight) that became extinct during the late Pleistocene did so by about 10,800 to 10,000 years ago. Whether the cause of this decimation of Pleistocene fauna was climatic or cultural has been debated ever since another American investigator, Paul S. Martin, proposed the overkill hypothesis in the 1960s. Whatever the case, it seems appropriate on paleontological grounds to designate the beginning of a new epoch - the Holocene - at approximately 10,000 years ago. From Encyclopedia Britannica On-Line.) This first demographic era lasted from uncertain beginnings until the introduction of agriculture around 10,000 years ago.

The second demographic era was that of agriculture and animal husbandry, spanning a time from 8000 BC until the Industrial Revolution around 1830. This new way of life considerably improved the carrying capacity of the earth for us. The social unit was the extended family living in the family mansion and surrounded by the cultivated fields. Even young children were part of the work force doing simple tasks and thus, they were producers as well as consumers. The responsibilities of their upbringing was spread out in the extended family structure from parents, to grandparents and to other close relatives living together. Because of the change in carrying capacity, the base population increased to a new value and then leveled off again at the balance of high birthrate and high death rate. It should be noted that in most part of the Western world, our sense of values are deeply rooted in the Classical and in the Judeo-Christian traditions. According to the demographic conditions of our roots then we had to reproduce at our full biological potential in order to balance the high death rate and survive. It is quite possible that the idea of rendering everything sexual reproductive within the framework of a caring family reflects this ecological imperative of the second demographic era.

The third demographic era was that if industrialization. It is rather arbitrary to date the beginning of this era with 1830 because the Industrial revolution developed to its fuller form through many decades. Nonetheless, for practical purposes it will do. There were many changes taking place in this era. Urbanization was one of them bringing the work force closer to the factories. Agriculture has been mechanized through technologies using fossil fuels, coal, natural gas and more recently gasoline. Production in the factories was first made possible changing the energy of fossil fuels into steam, and then later into electricity. Because of urban living a new family structure developed, the nuclear family. Here the responsibilities of bringing up the children rested exclusively on the two parents, both of whom often had to work to make ends meet. The concepts of apartment living, and latchkey kids first belonged to this era. In a new complex world of the industrialized society it became necessary for the children to go to school for many years until they became able to join the work force. For these many years they remained consumers creating an extra burden on the nuclear family. New technologies brought a panacea of better living. As medical knowledge grew starting with better understanding of hygiene, the discovery of immunization against viral diseases, and the discovery of antibiotics against bacterial diseases, death rate has been reduced especially in terms of lowering child mortality. Since birthrate was not adjusted because of moral concerns rooted in the previous era, a demographic imbalance was produced resulting in an exponential population grows. Due to this imbalance, the human population, which was around one billion in 1830, more than doubled by 1945, the end of the second World War, and the end of the third demographic era.

Many of the conditions of the third era persisted into the fourth and last demographic era from 1945 to the present time. What is new in our time is the worldwide network of communication transcending the national boundaries and uniting humanity on a global scale. Further developments of medical technology enhanced the reduction of death rate, although there are signs that some of the magic bullets used in the past may loose their magic. The genome project and genetic engineering are important developments for our future. Urbanization continues to rise creating heavy economic and social problems for many large cities. The impact on earth of humanity’s numbers and way of life shows its negative effects on major most systems the earth provides for us. Human life on earth depends on these systems. There is a decline in fertility and many nations, especially in the European Union reached zero population growth. We experience today, what demographers call a demographic transition from exponential growth to a new balanced situation, hopefully not beyond the carrying capacity of the earth.


Concepts and definitions.

We have experienced in the twentieth century an unprecedented population growth. We entered the century with well over one billion people and by the end of the century there were six billion. Numbers can show the momentum of this exponential growth. In 1830 there were one billion people on the earth. In 1930 there were two billion. In 1960, three billion. In 1975, four billion. In 1886, five billion. In the year 2000 we reached and passed 6 billion. The characteristics of growth can be visualized by figuring the number of years needed to add one more billion to the human population.

Without going into too much detail here, in summary we have the following data for world population today.


World 6137 22 9 1.3 54
More Developed 1193 11 10 0.1 700
Less Developed 4944 25 8 1.7 41
Less Developed minus China 3671 28 9 1.9 37

A = population in millions. B = Birthrate. C = Death rate. D = Growth rate
E = approximate doubling time. Birthrate is calculated as number of births per thousand population at the midpoint of the year, July 1. Death rate is calculated in a similar manner. Growth rate is calculated as the difference between birthrate and death rate expressed as percent.

It is important to emphasize that never in human history have we experienced such an enormous population growth as in the twentieth century. This growth resulted in an very large base population, with an equally large impact on the earth and its resources. This is an ecological problem, and it cannot be reduced to some economic or purely social issues, or to some magic of technology. It is unfortunate that most of our moral sense, most of our values, come from an era when maximization of reproductive success was essential for survival to balance high death rates in a relatively small base population. In our time, the much needed concern is reproductive restraint, with new sets of values and behaviors adjusted to the new conditions of life.

It is also important to realize the momentum of growth. This momentum can be seen in the doubling time of population size for a large base population. The practical formula to calculate doubling time in years for the human population is seventy divided by the percent of growth per year. Short doubling time would not matter too much in a small population. Our base population today is large, over 6 billion. The growthrate per year is 1.3%. If trends do not change we can expect close to 12 billion people in the world by the year 2054, a rather unrealistic scenario in terms of available resources.

Fortunately, attitudes do change. We do promote a process of demographic transition and are moving toward a new balance. (See essay: A Strategy of Change.)

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