High Quality Content by WIKIPEDIA articles! Zero population growth, sometimes abbreviated ZPG, (also called the replacement level of fertility)[1]is a condition of demographic balance where the number of people in a specified population neither grows nor declines, considered as a social aim. Zero population growth is the ideal to which countries and the whole world should aspire, according to some, in the interests of accomplishing long-term environmental sustainability. A loosely defined goal of ZPG was to have a fertility rate of 2.11 meaning a couple would have no more than 2(.11) children to replace themselves, the .11 is to prevent infertility or early death from lowering the current/future population levels. In this world of legalized divorce, that definition should be revised to say each adult would have no more than 2(.11) children with one or more spouses.In less developed countries (LDC), the replacement level of fertility is often as high as six children per couple.