<P> Some commentators disagree with the concept of "optimum population", believing that the human population will always, in the long - term, be able to adapt to the requirements of a larger population . </P> <P> Any conception of an optimum population level must lie between a minimum viable population of the human species and the maximum level of population that can be sustained by the carrying capacity of the planet Earth . </P> <P> Various end - targets are often balanced together in estimating the optimum human population, and different emphasis on different end - targets cause variability among estimates . </P> <P> The optimal world population has been estimated by a team co-authored by Paul R. Ehrlich . End - targets in this estimation included: </P>

When is a country thought to have an optimum population