Recently, the environmental situation in many of developing countries has deteriorated. These countries have confronted with overcrowding population, environmental degradation and poverty. In this report, we shall concentrate our attention on the environment of common pool resources (CPRs), which are characterized by non-excludability and rivalness. Some environmental issues of CPRs are mainly due to externality of CPRs. We shall prove that the environmental and population-related problem should be solved from these aspects. In this paper, we first study several factors which affect the scale of population. Next, we shall set a hypothesis concerning the familism (the family system), which affects the size of family and the scale of population significantly. Moreover, we also hypothesize the existence of an optimum family size and an optimum population determined by an optimum family size. Then we study the issues both by theoretical approach and empirical analysis. Finally, we prove some conclusions about the population size to be consistent with environmental preservation.

JEL classification : Q50, Q56