Do you know how many people there were in the world 200 years ago? Just one billion. But only 100 years later, the population was increased by 100percent. In 1971, about 3. 5 billion people lived on the earth. Forty years later, the number doubled(翻倍). On October 31st, 2011, the 7 billionth world citizen (公民), a baby girl was born in the Philippines(菲律宾). At this speed, it will shoot up to 8 billion by the year 2025.
Most new babies were born in developing countries. Most families have four or five children. In many developed countries, the population is increasing slowly. Most families have only one or two babies. In 1950, about 25 percent of the world's population lived in developed countries. By 2050, the number will reduce to 10 percent. In many developing countries, people are now short of food, water and medicine. What's worse, farmland is becoming less and less, and farmers are moving to cities to make a living. But cities couldn't satisfy their needs at all. Finally, many people can't find jobs, and they become poorer and poorer.
To solve these problems, many developing countries are taking measures to control the population.
