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We can understand facts about fertility by considering a small, contained population. Let’s imagine a remote--and unique--island populated by 2,000 children, half girls, half boys. As they grow older they pair and have children. By age 30 they have had 2,000 children--half girls, half boys--and have no more. The island’s fertility rate is 2.0 (2,000 children divided by 1,000 women) and its population is 4,000. |
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FERTILITY PRIMER
Imagine the second generation of 2,000 children pair and have children. By age 30 they have had 2,000 children and have no more. The island’s fertility rate remains 2.0 and its population is 6,000.
Imagine the third generation pair and have children and the first generation begins dying at the same rate as a fourth generation is born. For each birth there is a death. For each death, there is a birth. As a result, the population of our imaginary island remains stable at 6,000. A fertility rate of 2.0 is one element of a stable population.
Imagine another island populated by 2,000 children. As they grow older they pair and have children. By age 30 they have had 4,000 children and have no more. The island’s fertility rate is 4.0 (4,000 children divided by 1,000 women) and its population is 6,000.
Imagine the second generation of 4,000 children pair and have children. By age 30 they have had 8,000 children and have no more. The island’s fertility rate remains 4.0 and its population is 14,000.
Imagine as the third generation pair and have children, the first generation begins dying. When the first generation is gone, the population is reduced by 2,000, but with the fourth generation of children added, the population is 26,000. The fertility rate is twice that of our first island, but its population is more than four times as large -- and it continues to grow! Fertility rates matter! |
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©2010 Californians for Population Stabilization. All Rights Reserved
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