Utilitarian population ethics and births timing.

Summary Births postponement is a key demographic trend of the last decades. To examine its social desirability, we study how utilitarian criteria rank histories equal on all dimensions except the age at which individuals give birth to their children. We develop a T-period dynamic overlapping generations economy with a fixed living space, where individual welfare is increasing in the available space per head, and where agents have children in one out of two fertility periods. When comparing finite histories with an equal total number of life-periods, classical, average and critical-level utilitarian criteria select the same fertility timing, i.e. the one leading to the most smoothed population path. When comparing infinite histories with stationary population sizes, utilitarian criteria may select different birth timings, depending on individual utility functions. Those results are compared with the ones obtained when agents value coexistence time with their descendants. Finally, we identify conditions under which a shift from an early births regime to a late births regime is socially desirable.