The "tragedy of the commons," which is an expression of the externalities associated with a failure of societies to price a scarce good, has served as an illuminating metaphor for our excessive use of the biosphere. However, social scientists have not translated the excessive use of the commons into the analysis of our reproductive behaviour. In his lecture, Sir Partha Dasgupta will first develop an account of the feedback and then point to a class of externalities that arise from the social-embeddedness of our preferences for both consumption and reproduction. The latter externalities have a different character to the ones experienced in the commons and can be weakened by civic engagement, they do not require centralized tools such as taxes and subsidies.