>>28849906Regular evolution is more akin to the Pokemon growing from child to adult. Megas are evolution in the conventional sense, as in how the adult form would look in the future through physical adaptation, accelerated by the mega stone. It's not really environmental adaptation since it's tied to the trainer, thus optimizing the Pokemon for battle rather than survival.
Pokemon with stone evolutions can probably evolve without them, but it takes longer than the game's duration, as you're still a kid in the end. Evolution stones just give them a burst of elemental energy that they would normally collect over a lifetime, accelerating the process, but because it skips their natural development they lose access to level up moves. Only a handful of Pokemon evolve through elemental energy like this, obviously.
Mega stones, which are meteorite shards, similarly give Pokemon enough energy to evolve rapidly, but the mega energy works with many species, if not all. The meteorite radiates mega energy, but different parts of the meteorite randomly resonate with a specific Pokemon, or match their energy signature, or whatever. That's why the stones are specific. The mega sigil resembles a double helix and the crystals inside the stones, so it's possible the meteorite contains some primitive DNA structures that match certain Pokemon. It's possible that more than one structure can match a Pokemon and reflect a different evolutionary path, hence Charizard X and Y. Or the stone is modified like Origins suggests.
