The long, nearly flat population curves in certainly masks a number of small-scale trends, both upward and downward. The fossil record is not rich enough to plot a detailed record, but surely at times when weather was pleasant and food from plants and animals was abundant, the human population must have risen. Conversely, when weather was harsh, food was scarce, and diseases were rampant, the human population must have fallen.
The nearly flat population growth curve began to rise more rapidly by about 8,000 years ago when agriculture became established and numerous species of animals were domesticated. The world population is estimated to have been about 8 million people by 10,000 years ago. After the development of agriculture and the taming of animals removed much of the hardship form human existence, the population growth rate is likely to have increased from about 0.0015 percent to 0.036 percent per year, yielding a net gain of 360 people per million per year. This heightened rate of population growth probably raised the number of humans to about 200 million alive at 2,000 years ago.
As humans continued to improve their ability to modify the environment with better shelter and more reliable food and water supplies, the world population grew at faster rates. From about1C.E to 1750, world population grew to about 800 million. Growth was at an average rate of 0.056 percent per year, or another 560 people were added per million per year.
The eighteenth century saw many of the intellectual advances that set the stage for the present phase of cultural change. At long last, the causes of many diseases were being recognized, and the principles of public health were being established. Advances in the medical world greatly improved the odds for the survival of individual humans through their reproductive years. No longer were many mothers and great numbers of children dying childbirth and infancy. Throughout the history of the human race, high rates of birth were required to offset high rates of infant mortality and thus maintain a viable- sized human population.
The eighteenth century saw death rates drop dramatically, but birth rates remained high and population doubling times dropped dramatically, thus population size soared. About 1810, the human population reached 1 billion; by 1925, it had grown to 2 billion; in 1960, it reached 3 billion; by 1974, it was 4 billion; by early 1987, it was 5 billion; in 1999, it reached 6 billion, and is heading toward 7 billion in 2012. Notice the continuing decline in the number of years it takes for a net gain for another I billion people on earth; the effect of exponential growth is racing ahead.
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