Introduction.
About 155 people are born every minute of every day. This recent rise in population is often called the population explosion. If the rate of growth continues, the world's population will have trebled by a he end of the century. 
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World population grew much more slowly in the past. It took about 11,500 years for it to grow from 10 million to 500 million. Since 1800 it has grown very quickly.
• in 8000 b.c there were probably only about 6 million people in the world. Most lived in Asia and Africa.
• by a.d 1, people had spread to most parts of the world. The population had grown to about 255 million.
• by 1600 the world population had doubled to about 500 million.
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In 1987 the world population rose to 5 billion, ten times as many people as in 1600. About three- fourths of the world 's people today live in Asia and Eroupe.
• At its present rate of growth, the world population doubles about every 40 years.