According to the classical definition,given by United Nations World Commission on Environment and Development in 1987, development is sustainable if it "meets the need of the present without compromising the ability of future generation to meet their own needs." It is usually understood that this "intergenerational" justice would be impossible to achieve in the absence of present-day social justice, if the economic activities of some groups of people continue to jeopardize the well-being of people belonging to other groups or living in other parts of the world. Imagine,for example, that continuing deforestation of the Amazon basin, know for its outstanding biodiversity, leads to the extinction of an unresearched plant species that could help cure acquired immune deficiency syndrome (AIDS), a lethal disease threatening people all over the world. Or