It's really quite dependent on the Pokemon, or so I've read.
[[Crossing her arms, Page examines Astrid's Pokemon with a curious eye. None of hers have undergone evolution, yet, so the subject is one she's quite interested in. She usually wouldn't go out of her way to engage a stranger, but....well, perhaps this girl has some worthwhile information about the subject, since she's obviously had some experience with it.]]
If they don't want to evolve, you can't force it. You have to let them decide for themselves if it's what they want.
...I don't quite understand it all myself, but I believe that's the basic gist of it.
[action - if that's alright!]
[[Crossing her arms, Page examines Astrid's Pokemon with a curious eye. None of hers have undergone evolution, yet, so the subject is one she's quite interested in. She usually wouldn't go out of her way to engage a stranger, but....well, perhaps this girl has some worthwhile information about the subject, since she's obviously had some experience with it.]]
If they don't want to evolve, you can't force it. You have to let them decide for themselves if it's what they want.
...I don't quite understand it all myself, but I believe that's the basic gist of it.