Repair-contributor loss sustains tissue damage

Ageing may make tissue damage self-sustaining. This hypothesis asks whether support-cell mix sets the tipping point. Stromal cells maintain tissue support. Repair contributors may restore it at their own expense. The proposed mechanism uses frequency-dependent selection: a behaviour’s advantage changes with its share. Above a critical share, contributors would expand and damage subside in linked tissues; below it, they would decline and damage would recur. The test holds total cell number, starting damage and daily load constant while varying the initial contributor share. It predicts opposite long-term trajectories around one threshold. Fixing composition should remove the transition, separating this proposed cause of persistent damage from rival explanations.