I think evolution in the anime is a bit more realistic than in the games. Because let's face it every game has to have it's limitations as to what it can do. Does it really matter if a Pokemon evolves randomly?
That's a tad unfair because Misty's Poliwhirl didn't evolve like nothing. What the anime did (they did this for that Clamperl episode), was tranfer the Pokemon from one place to another is probably enough to be considered "trade evolutions."
So in other words, trading and stones mean nothing and all Pokemon can evolve naturally like Exeggute and Misty's Poliwhirl
Remember in the episode Misty's Poliwhirl evolved. Do remember how it had the king's rock and there was a time they didn't have any of their Pokemon with them when Team Rocket stole the guy's Poliwrath. Then they went to the Pokemon Center on the side of the road, and called the town's Pokemon center and they transfered their Pokemon to them, then the next time Misty sends out Poliwhirl it evolves. I think just the transference of one Pokemon Center to another (in the anime) was enough to trigger the evolution.
And also just because we don't see a full stone, it doesn't mean it didn't evolve that way, there could of been tiny bits of leaf stone in the air or in the soil.
I also think in the anime there are different methods of triggering evolution. At least it's the case with Slowbro and Slowking. So maybe if the wild Pokemon had enough power it could just evolve on their own. Or maybe with stone induced evolutions, there could be similar radiation objects out there.
How would stone-induced/item-induced (King's Rock, etc) and trade evolution work in the wild? For example, if a wild Pikachu wanted to evolve or a wild Kadabra?
Or maybe the wild Pikachu worship a gigantic thunder stone, once a month and only the lucky chosen ones get to evolve into Raichu.
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