Fig. 1. Partial and complete rejuvenation.
At advanced ages, aging is associated with several hallmarks (shown by 7 circles), which may be targeted by certain candidate interventions (shown next to each circle), thereby slightly reducing the biological age of an organism. However, since these approaches affect only some pathways, cells or organ systems, without affecting others, they may only lead to fragmentary or partial rejuvenation. In contrast, complete rejuvenation (shown by a large circle in the middle of the figure) should reset the age of all cells and systems, such that the organism becomes essentially indistinguishable from the same organism in the much younger state.