Degenerative diseases of ageing as problems of natural selection. A commentary upon the concept of 'normal ageing'.

(1) The field of experimental gerontology is reviewed in relation to past and current views on the definitions and origins of degenerative diseases in relation to ageing. (2) It is concluded that the present concensus defines age-related degeneration of cells, tissues and failures of homeostasis as expressions of the accumulation of chemical and metabolic errors, which cause deviations from the precise structural specifications of youth. (3) Errors accumulate because to commit resources to correct them would reduce the materials and energy that could be devoted to reproduction. (4) The evolutionary perspective is that the balance between error correction and reproduction was set by natural selection in past environments where most members of the population died from accidental death, at, or close to, peak reproductive performance. (5) This opens up a theoretical pharmacological perspective where it might be possible to treat degenerative diseases by the activation of error detection and repair mechanisms.