I think the point they were making with evolution was that once the Pokémon evolves, it becomes an entirely different being. That's why in the anime Pikachu refused to evolve. It saw what Raichu had become, and I suspect that Pikachu felt that it had changed somehow in both mind and spirit.
I'm probably just reaching for some literary meaning that doesn't actually exist in the show—it is a child's show, after all—but it could also be commentary on the state of our being. Humanity has made incredible advancements in every direction. So much so that we no longer resemble our ancestors who crawled out of the sea.