>>33744549ToTT: While I haven't dug all that much into it, evolution can have far reaching physical and mental effects on a pokemon, and both of these can influence the relationship it has with its peers, its trainer, and with its own perception of itself.
Evolution will generally come with increased maturity and a shift in personality to reflect this, but what is difficult to account for is the myriad ways that pokemon can change, be it subtly or drastically, when they evolve. Imagine a Beldum moving to a Metang to a Metagross - it supposedly goes from 1 brain to 2 brains to 4 brains, and that has incredible consequences attached to it.
Contrast that to the evolution of a Diglett to a Dugtrio, and both pokemon will have very different ways of striking an author in how to handle their evolution. At least, that's how I see it. I would rather take evolution on a case by case basis with a few very, very general rules, than apply any kind of blanket to them.