This is Gwen Outen with the VOA Special English Development Report.

New research shows that Earth will have more than 9000 million people by 2050. The world population is currently estimated at 6.4 thousand million.

The research is from the Population Reference Bureau, a private group based in Washington. It says most growth will take place in developing countries in Africa and western Asia.

India is expected to pass China as the world's most populated nation. By the middle of the century, the report says, India will have over one and one-half thousand million citizens, an increase of fifty percent.

China currently has one 1.3 thousand million people. The Population Reference Bureau says the population should increase about ten percent by 2050.

Most industrial nations will see a drop in their populations. The only big exception is expected to be the United States. The report says the United States will remain the third biggest nation. The population is close to 300 million now. It is expected to reach 420 million. The report says this will be because of immigration and low death rates among babies.

Between now and 2050, Niger is expected to be the fastest growing country. The biggest decrease is expected in Bulgaria.

The study is based on information from governments and the United Nations. Researcher Carl Haub wrote the report. He examined infant death rates, life expectancy, birth rates and the age structure of nations. The study also considered family planning use and, for the first time, rates of AIDS.

Mister Haub says most growth will take place in countries with young populations and traditionally large families. He points to Nigeria and Japan as two nations that are moving in opposite directions in terms of population.

In Nigeria, almost half the people are under the age of 15. Few are over 65. Nigerian women generally give birth about 6 times during their lives. By comparison, the average Japanese woman has one child. And today about 20 percent of Japanese are over the age of 65.

Mister Haub expects the Japanese population to decrease by 20 percent. He estimates that the population of Nigeria will increase by more than 120 percent by the middle of the century.

This VOA Special English Development Report was written by Jill Moss. This is Gwen Outen.

life expectancy: an expected time to live as calculated on the basis of statistical probabilities（平均寿命）