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Like the populations of many other living organisms, the size of the human population tends to increase with time. For most of human existence, the population grew slowly. Life was harsh, and limiting factors kept population sizes low. Food was scarce. Incurable diseases were rampant. Until fairly recently, only half the children in the world survived to adulthood. Because death rates were so high, families had many children, just to make sure that some would survive.
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About 500 years ago, the human population began growing more rapidly. Agriculture and industry made life easier and safer. The world's food supply became more reliable, and essential goods could be shipped around the globe. Improved sanitation, medicine, and health care dramatically reduced the death rate and increased longevity. At the same time, birthrates in most places remained high. With these advances, the human population experienced exponential growth, as shown in the figure at right.
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Human Population Growth
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