Definitions of reversion:

• noun:   turning in the opposite direction
• noun:   a return to a normal phenotype (usually resulting from a second mutation)
• noun:   (law) an interest in an estate that reverts to the grantor (or his heirs) at the end of some period (e.g., the death of the grantee)
• noun:   a reappearance of an earlier characteristic
• noun:   returning to a former state
• noun:   a failure to maintain a higher state