Why Do We Actually Die?: Evolution, Aging, and Disease.

This essay asks why humans age and die, and answers from the standpoint of evolutionary biology. Natural selection acts strongly on traits that affect survival and reproduction up to reproductive age, but only weakly on what happens afterward. Three complementary theories - mutation accumulation, antagonistic pleiotropy, and the disposable soma - explain why the body is not built to be maintained indefinitely. In this picture, cancer, cardiovascular disease, type 2 diabetes, and dementia are neither punishments nor isolated defects but line items on a single bill: the price of a body shaped to pass on genes, not to last. The essay also shows why the bill is not fixed (elephants, the role of grandmothers, prevention, and early detection), why life expectancy has risen without abolishing aging, and why the roles of stress and heredity are often overstated. It is a popular-science essay based on published sources, not original research, and it has not been peer reviewed.