So, in an episode of the Sinnoh anime, there is an episode where Dawn’s Piplup is seeming sickly and tired all of the time, and disappears during the night. It turns out that Piplup is about to evolve, however, it uses the move Bide to keep itself from doing so. When the evolution process finally starts in battle, Dawn is at first very excited, but then confused when Piplup bides the evolution away. Do you think this raises some interesting questions on a Pokemon’s control of evolution?

Hmm.  Interesting.  I will note that I’ve seen hardly any of the Sinnoh series and don’t really know anything about Piplup’s portrayal as a character, but putting that aside…

In some ways it’s a similar situation to what Bulbasaur faced in Bulbasaur’s Mysterious Garden, except that here the pressure to evolve is internal, not external.  My usual position on evolution is that it’s triggered at least partially by a state of psychological readiness (with certain exceptions, such as the use of evolutionary stones or the evolution ritual in the Mysterious Garden) so on the one hand, it makes sense for Piplup to be able to hold it off by an act of will, but on the other hand, in the absence of any obvious external stimulus, I have to wonder what was causing Piplup to evolve in the first place.  Maybe a subconscious desire for growth and strength was prompting the change in body chemistry that triggers evolution, but on a conscious level Piplup didn’t actually want to evolve – he wanted to get stronger in his current form.  The conflict would be enough to forestall evolution indefinitely, but at the cost of maintaining a heightened state of stress which would normally be associated with a short burst of rapid growth, hence Piplup’s weakened state.

What I seem to be saying here is that Pokémon don’t normally ‘choose’ when to evolve, per se; although it will usually happen partly because they want it to, it’s triggered by psychological factors outside of their conscious control.  Normally evolution takes place in moments of heightened emotion – it might be a rush of adrenaline that pushes them over.  A Pokémon who understands the process might be able to cultivate deliberately the kind of mental state that prompts evolution – or, in Piplup’s case, force himself to calm down and slow the process.