**2. Aging and lifespan**

Aging is a natural universal phenomenon affecting all living organisms (e.g., plants, animals, and humans). It is a progressive deterioration of the cell and organ functioning due to damage accumulation over time. The exact underlying mechanisms of aging at the cellular level are not fully understood. The most popular theory is the free radical theory [7].

Lifespan is a biological characteristic of every species. However, it can be modified by mutations or by a variety of interventions (e.g., lifestyle, pharmacological, stem cell, and genetic interventions) [8–24].

Lifespan of living organisms ranges from few hours (animals) to few thousand years (plants). Phenotypic plasticity can affect the long lifespan of both plants and animals [25].
