Why do we age? The fundamental causes of aging at the molecular level are relatively well established , and have been addressed on the podcast before . One example is the loss of protein homeostasis , which contributes to misfolded proteins ( a characteristic exhibited in neurodegenerative diseases like Alzheimer’s ). Another example is the accumulation of senescent cells, which induces chronic inflammation and contribute to functional decline of tissue over time . So we understand, to some extent, how aging happens, and the proximal causes of the time-related decline of physiological function that all of us experience. But the question of why aging happens in the first place is a more challenging one, one which has bedeviled evolutionary biologists and philosophers for years. You might think, intuitively, that the process of natural selection would gradually remove individuals that were subject to these signs of senescence. Aging increases mortality, and organisms that ex