Is eternity sufficient?

Why does life manifest itself through a succession of mortal individuals rather than through a single living being able to persist indefinitely? And why does life consist of a plurality of species rather than a single form? The essay examines four possible answers: an internal insufficiency of the being, an external value or end, a logical or physical impossibility, and the hypothesis that the existing configuration is a brute fact with no further reason. Particular attention is given to the idea that imperfection and the need for improvement over time might justify the structure of life, to the problem of the origin of an eternal being, to the thermodynamic objection formulated in probabilistic terms, and to the identity of a spatially distributed being. The result is bounded: the arguments examined do not show that mortality, succession and plurality are absolute necessities. The analysis shows, however, that indefinite persistence depends on residual risk, and that probabilistic results must be referred separately to three configurations: the single individual, the integrated system and the lineage. For a single individual under a constant non-zero risk, persistence has probability zero; an integrated system may reduce its overall risk through repair, redundancy and regeneration; a lineage may persist with positive probability without thereby requiring a plurality of species. The non-necessity of succession therefore depends on the physical possibility that the individual or the integrated system have a finite cumulative risk; the non-necessity of species plurality does not depend on it, since the model is compatible with a lineage that does not diversify, though it does not guarantee that it remains a single species over time. The essay thus clarifies the conditions that a proof of the impossibility of an eternal being would have to meet.