8. What are hallmarks of aging?

The hallmarks of aging framework is a useful checklist of recurring molecular and cellular changes, especially for organizing experiments and interventions (e.g., genomic instability, loss of proteostasis, senescence, inflammation). It is not a definition of aging or the essence of aging. In a systemic view, many hallmarks are interdependent manifestations of deeper constraints (imperfectness, finite maintenance, tradeoffs), and they mix drivers, compensations, and consequences. Also, boundaries between hallmarks are fuzzy, the same change can be protective in one context and deleterious in another, and the framework can encourage a single-hallmark thinking instead of systemic thinking. Used carefully, hallmarks are a map of recurring phenomena in aging and can be interpreted as partially overlapping projections or manifestations of the broader deleteriome.