| Wear-and-tear effects |
After a certain amount of time, the living organism becomes 'unusable', stops working and dies. (The following theories can be summarized under this general theory.) |
| Immune function impairment |
Impairment of immune function results in disease and death. Ageing may represent deterioration in immune ability. |
| Somatic mutation |
Accumulated damage to cellular components results in altered cellular function. Ageing may represent accumulated cellular damage at the molecular level. |
| Free radicals |
Highly reactive, oxidative free radicals damage cellular components. Ageing may represent accumulated damage from free radicals. |
| Cross-linkage of macromolecules |
Abnormal chemical bonds form between cellular structures and cellular components, such as collagen, and result in altered cellular function. Ageing may represent accumulated damage in macromolecules. |
| Metabolic causes |
Metabolic exhaustion causes deterioration of the organism. Ageing may represent metabolic depletion. |
| Species-specific restricted ability of cells to divide |
This theory is based on the observation that normal cells in tissue culture only divide a defined number of times and then die. |
| Genetic programme theory |
Lifespan concluded by death is a genetically determined characteristic. |
