şu sayfada bir bilgi var,
www.npg.orgConsidering food production, the load that human activities are imposing on the biosphere, global warming, chemicals and pollution, labor and wages, issues of social equity, and the problems of crowding, disease, and misery, NPG believes that a world population size of two to three billion would be optimal.
2-3 milyar denmiş, bir kaç yerde daha bu şekilde geçiyor.