Review of related Literature
As can be seen in Figure 1, the world's population grew very slowly until about 1750. There was a long period of stationary growth (no growth) until 1000 B.C.E., when the world's population was approximately 300 million; this was followed by a period of slow growth from 1000 B.C.E. to approximately 1750, at which time global population was an estimated 800 million. Until this time, the world's population was kept in check by high death rates, which were due to the combined effects of plagues, famines, unsanitary living conditions, and general poverty. After 1750, the world's population grew substantially; by 1950 it had tripled to around 2.5 billion. In this 200-year period, the doubling time was 122 years. Growth from 1950 to 1985 was even more dramatic; by 1985, the human population was 5 billion. World population had doubled in thirty-five years. By 2000 global population was 6 billion and is projected to be 9 billion in 2050. Population growth did not become exponential until around 1750. Before that, high mortality counterbalanced the high fertility needed by agrarian parents. Death rates were high and life expectancy was low; life expectancy at birth was in the range of twenty to forty years (most likely around thirty years) until the middle of the eighteenth century. This high mortality was a function of several factors, including poor nutrition, which led directly to deaths through starvation and indirectly through increasing susceptibility to disease; epidemics; and, quite possibly, infanticide and geronticide, especially during times of food shortage. Starting in the middle of the eighteenth century, the mortality rate began to decline in the West, the first place in the world where the natural balance between births and deaths was altered by humans. This decline in deaths occurred not because of major medical breakthroughs (e.g., penicillin was first used only in the 1940s) but rather because of improvements in food availability, housing, water cleanliness, personal hygiene, and public sanitation. Later, in the twentieth century, medical advances, particularly vaccinations against infectious diseases, accelerated mortality decline.
Western mortality decline was relatively slow, paralleling socioeconomic development, and it occurred in a global context in which European population "surplus" (arising from gaps between lowering mortality and more slowly lowering fertility) was able to migrate to new areas (e.g., the United States, Canada, and Australia) that were very sparsely populated by Aboriginal peoples (whose numbers were reduced even more by contagious diseases brought by Europeans). Mortality decline in less developed countries followed a different path. First, mortality decreases did not begin until around 1950, much later than in the West. Second, in many less developed countries, substantial mortality reductions occurred in a short period of time. A classic example is Ceylon (now Sri Lanka), where the death rate was halved in less than a decade, starting in the early 1950s. (In the West, a comparable reduction typically took around one century.) In these less developed countries, mortality decreases were not matched by fertility decreases, where they produce population growth rates much greater than those experienced in the West. So the demographic transition that took two centuries to unfold in the West occurred (or is occurring) within the span of a single life. Third, mortality decline did not parallel economic development. Rather, the impetus behind third world mortality reductions originated, for the most part, in factors external to the society. For example, the speedy mortality decline in Ceylon was due to the importation of American technology (pesticides and the airplanes for spraying them) that killed the mosquitoes that were responsible for malaria, the leading cause of death. During the cold war, it was not uncommon for the United States...
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