Generation time as optimal stopping time

The timing of peak reproductive effort is a central problem in life-history theory, yet a simple first-principles target for that timing relative to lifespan has been missing. We propose that generation time is an optimal stopping time. Under the 1/e-law of best choice, the unique strategy that guarantees the highest minimum probability of selecting a superior option is to wait until a cumulative fraction 1/e of opportunities has passed. When reproductive opportunities arrive in an approximately time-homogeneous way over adult life, that threshold is 1/e (about 37%) of maximum lifespan. This fraction is confirmed by standard population dynamics for indeterminate growers, combining von Bertalanffy growth with constant mortality. A compilation of published reproductive schedules in plants, animals, and humans illustrates the predicted alignment across taxa and absolute timescales. The 1/e-law thus supplies an organizing quantitative account of a core life-history schedule.