Abbreviated ZPG, it’s an international movement for population control. It had its beginnings in an organization formed in 1968 called Zero Population Growth, which was established with the help of American biologist Paul Ehrlich (1932-). In his book The Population Bomb (1968), Ehrlich argues that the world’s population is growing at a pace that will outstrip its supply of natural resources, reaching the conclusion that overpopulation will inevitably cause widespread starvation and death. While his critics charge that this is an oversimplification of the situation, Ehrlich and others who subscribe to his views argue that overpopulation may not be the only factor leading to a severe shortage of natural resources around the globe, but it surely is the most important. The movement urges parents to have no more than two children; at this rate (called a replacement rate) there would be no population growth. In the late 1990s researchers reported that in the United States and in much of Europe, the birth rate is below replacement level, while in some of the world’s poorer countries, the average birth rate can be as high as eight children per woman.