When talking about Pokémon, fans (and maybe some non-fans) will surely be familiar with the process of evolution, as the changing of species from a lesser form to a greater form. What is rarely talked about is the reverse, which is called "devolution" by analogue. It's obvious why few people talk about it, since no one really wants their evolved Pokémon to "devolve". Yet the process exists in certain ways, and it deserves a bit of discussion.
The process has come into its own in the TCG - particularly most recently - with some cards that command the process to be performed by removing the top evolution card of a Pokémon, forcing it to devolve to the prior stage. It's a bit of a nasty trick, but then the cards that enable this to happen are also relatively few; it's still a trick for players to look out for because the results and side effects may be as unwanted as the process itself.
Meanwhile, outside of the games, the anime has depicted "devolution" - albeit in an illusory fashion - with some Pokémon seeing the lesser forms of themselves through some prompted imagery. Like the cards in the TCG, though, instances of these are few and admittedly not as memorable (or even definitive) as other scenes, including those that depict the inverse process - even if it's still somehow possible through certain Pokémon powers.
Given the constraints of the process, it can be seen why the process is not often evident. It represents a physical reversion that in real life and practically derived settings would be impossible to do. In most cases, the process is (or would be) almost "tantamount" to time travel, which even with some Pokémon powers in play is still limited in capacity and may not necessarily have the expected and intended effects for the process.
Still, the existence of the "devolution" process may be considered a demonstration of what some Pokémon species may actually be capable of, even if that may not be all that evident or practical for them in whatever settings they are involved. Evolution as its inverse will remain the dominant process of Pokémon development as is true of the reality that moves ever forward, yet some "backwardness" may serve as an added intrigue.
One year ago: PokéParkour
Two years ago: Moon Matters, Pokémon Matters
Three years ago: From Draft to Post: The Thought Process of Pokémon Blogging
Four years ago: Pokémon Unite Halloween Event
Five years ago: Being a Scanner or Diver with Pokémon
Six years ago: On Tap for Go
Seven years ago: Pokémon Go Community Day Repeat, 10/28/2018



