For decades, the standard scientific explanation for ageing has been almost apologetically vague: it is a "complex, multifactorial process" involving a slow accumulation of cellular errors. This view suggests that our bodies simply wear out, like old machinery, due to unavoidable DNA damage and toxic by-products. However, a unifying new "four process model" suggests that ageing is not a random slide into chaos, but a structured sequence of biological events driven by the forces of natural selection occurring within our own tissues.