In the community that comprises a multicellular organism, dying gracefully is a dignified last task. Knowing that their life is ending, cells request their replacement.
Like all organic entities, cells have a limited lifetime. Apoptosis is a form of programmed cell death that occurs in all multicellular organisms. Many diseases trace to botched apoptosis.
A cell manages many biochemical events on its way out. One is to place a protein marker on the cell’s membrane that signals the immune system of imminent demise.
Immune cells arrive to provide protection and reassurance. The dying cell then requests a successor.
So multicellular organisms smoothly outlive the individual cells of which they are comprised, until terminal fatigue overtakes the entire ensemble, and an organism discovers its own mortality.
Alla Amcheslavsky et al, “Transiently ‘undead’ enterocytes mediate homeostatic tissue turnover in the adult Drosophila midgut,” Cell Reports (24 November 2020).
“Cells in limbo rouse allies before they perish,” Nature (25 November 2020).