degeneration

noun

• The process or state of growing worse, or the state of having become worse.
• That condition of a tissue or an organ in which its vitality has become either diminished or perverted; a substitution of a lower for a higher form of structure.

  "fatty degeneration of the liver"

• Gradual deterioration, from natural causes, of any class of animals or plants or any particular organ or organs; hereditary degradation of type.
• A thing that has degenerated.