This is because much of what makes us older is not the age of our cells but the deterioration of the systems that generate them. Aging is the cellular equivalent of playing telephone: each generation of cells does not quite regenerate the structure it inherited and so mistakes and imperfections creep in. My skin has aged not because my skin cells are forty-three years old—they are not; they are constantly being replaced with new cells generated by my adult stem cells—but because, over time, problems and imperfections have developed in the structure of my skin and have then been passed from one
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