Pokémon FireRed and LeafGreen/Evolution
From StrategyWiki, the video game walkthrough and strategy guide wiki
Evolution is when Pokémon change forms. There are many different ways this happens:
Items
When some Pokémon are given items they evolve.
Trading with Items
Rare items are known to evolve Pokémon but only if they are traded with the item
Stones
Leaf, Sun, Moon, Fire, Thunder, and Water Stones also evolve Pokémon.
Random
Random evolution occurs when one Pokémon may turn into one of two different Pokémon.
Taming
When Pokémon are happy enough they might evolve.
Day/Night
Some Pokémon evolve whether it is day or night, this does not work with FireRed/LeafGreen because they don't have an in-game clock so you must trade the Pokémon over to Ruby/Sapphire.
