From the OED:
obsolescence, n.
1. a. The process or fact of becoming obsolete or outdated, or of falling into disuse.
b. spec. The process whereby or state at which machinery, consumer goods, etc., become obsolete as a result of technological advances, changes in demand, etc. Cf. planned obsolescence s.v. PLANNED ppl. a. 2.
2. Biol. and Med.a. The gradual disappearance or atrophy of an organ or part; persistence of an organ, tissue, etc., without function or activity; (also) spec. the penultimate stage in the evolutionary loss of a character, or in the extinction of a species.