Theseus's Paradox, Theseus ship
A metaphysical problem concerning the persistence of identity and change in objects
If there are Time-invariant parts in the Ship of Theseus that are never replaced, they could be considered the physical essence of that entity. In humans, while skin cells and many atoms of organs are replaced through digestion processes, the core neuronal structure of the brain, Cardiac muscle cells, and Lens protein in the eyes are never replaced at the atomic level throughout one's lifetime. Thus, we can consider the physical essence of a human to be the core framework excluding Neuroplasticity, heart muscle, and visual proteins.