retrogression

Etymology

noun

1. A deterioration or decline to a previous state.
   History and experience, the enshriners of the past, and investigation, the discoverer of the present and preparer for the future, will prevent retrogression. 1849, Hogg's Weekly Instructor, page 388
   Suns spring into being, and then their height of power being reached, the process of retrogression begins, and after aeons they become dead masses of matter, awaiting another impulse which starts again their inner energies into activity and a new solar life cycle is begun. 1908, The Three Initiates, The Kybalion: Hermetic Philosophy, archived from the original on 2011-08-27
2. (biology) A return to a less complex condition.