Methods of Evolution

There are numerous methods of evolution which define how and when Pokémon evolve. Most Pokémon will evolve by leveling up while others evolve through specific means, such as being traded, achieving a certain amount of happiness or leveling at certain times, among others.

Triggers

Across all generations, Pokémon may only evolve after one of three events:

Though these three are the activating events for evolution, there is always a catalyst required for the evolution to begin. If the catalyst is present and the evolutionary event is activated, the Pokémon will evolve at the end of the process that caused the activating event (at the end of a battle or after a trade has been completed). An Everstone held by the Pokémon will always prevent the evolution.

Leveling up

Most Pokémon that evolve do so after leveling up. This can be triggered by gaining experience in battle or by using a Rare Candy. Several additional conditions must be met in addition to gaining a level for a Pokémon to evolve, such as being at or above a specific level, knowing a move, or being in a specific place. It should be noted that a Pokémon left in the Daycare will not evolve, even if other conditions are met. When these conditions are met, a Pokémon will attempt to evolve every time it gains a level unless the conditions are removed.

Leveling up
Lotad	→ Level up	Lombre

At or above a certain level

Main article: List of Pokémon that evolve at or above a certain level

Most Pokémon, with at least one in nearly every evolution family, will evolve when they reach or surpass a certain level. A Pokémon that levels up to this level or a higher level will attempt to evolve every time it does so, at the end of the battle in which it attained this level or after a Rare Candy has been used.

When happiness is high

Some Pokémon will only evolve when their happiness reaches 220 or above and they are leveled up. This is most common with baby Pokémon; however, some others also evolve in this way. Like the happiness system itself, this method of evolution first debuted in Generation II. Like those which evolve when at or above a certain level, a happy Pokémon will attempt to evolve every level until it hits level 100, unless its happiness is reduced.

The Spiky-eared Pichu in Pokémon HeartGold and SoulSilver is an exception, and will never evolve.

Happiness
Togepi	→ Happiness	Togetic

When the Pokémon knows a certain move

Some Pokémon evolve only if they currently known a certain move and are then leveled up. These moves are commonly available by leveling up (in which case the Pokémon will evolve at the end of the battle in which it learned the move), though some must be taught via move relearner. This method was introduced in Generation IV.

Knowing a move
Piloswine	→ Level up knowing AncientPower	Mamoswine

When trained in a certain area

Pokémon can evolve based upon their environment. Several evolutions introduced in Generation IV take advantage of this.

Leveling up somewhere
Nosepass	→ Level up in Mt. Coronet	Probopass

When holding an item

Several Pokémon evolve if they level up while holding a specific evolution-inducing held item. When this occurs, the item disappears upon completion of the evolution. Currently, every Pokémon who evolves in this way must also level up at a certain time.

Holding an item
Sneasel	→ Level up holding Razor Claw (Night)	Weavile

At certain times

The current time will sometimes affect evolution, but it is never the sole catalyst; it always is used in tandem with another (currently, happiness and a held item are the only ones it is paired with).

At certain times
Gligar	→ Level up holding Razor Fang (Night)	Gliscor

Unique conditions

The following Pokémon evolve through a method that is isolated to their evolution line only.

Mantyke evolves into Mantine when it levels up if there is a Remoraid in the user's party.
Feebas evolves into Milotic by leveling up if its Beauty stat is 170 or above.
Combee evolves into a Vespiquen at level 21 if it is female. Male Combee do not evolve.
When Nincada evolves into Ninjask at level 20, if there is an empty slot in the party, a Shedinja will appear. In Generation IV, the player must also have a spare Poké Ball in their bag.

Additional factors

Some Pokémon from branched evolution families evolve into different forms depending on some additional factors. These factors are not conditions for evolution, since they do not determine the possibility of evolution, but what the Pokémon will become after evolution.

Burmy evolves at level 20, but its new form is determined by its gender and cloak (and the cloak changes according to the place where it has battled last time).
- Male Burmy → Mothim
- Female Burmy → Wormadam, but the type combination of Wormadam is determined by the cloak.
  - With Plant cloak (after battling in the wild) → Bug/Grass Wormadam
  - With Sandy cloak (after battling in a cave or on a beach) → Bug/Ground Wormadam.
  - With Trash cloak (after battling in a building) → Bug/Steel Wormadam.

Tyrogue evolves at level 20, depending on his stats.
- If his Defense is higher than his Attack, he evolves into Hitmonchan.
- If his Attack is higher than his Defense, he evolves into Hitmonlee.
- If his Attack is equal to his Defense, he evolves into Hitmontop.

Wurmple evolves at level 7 into Silcoon or Cascoon, depending on its personality value. This value is hidden. It is determined when Pokémon is caught and cannot be affected by the player. See the article about personality value for the exact formula.

Evolving by evolutionary stone

Main article: Evolutionary stone

See also: Pokémon that evolve by evolutionary stone

Some Pokémon evolve when they are exposed to an evolutionary stone. The stone may be applied at any time and causes an instant evolution. The player can decide whether and when to evolve his or her Pokémon, but he or she must choose carefully as most Pokémon will no longer be able to learn certain moves when they evolve in this way, and some (like Raichu and Togekiss) cannot learn any moves by leveling up, although there are exceptions to this rule and certain moves are exclusive to the stone-evolved Pokémon.

The starter Pikachu on Pokémon Yellow (or any Pikachu with the same OT and ID number) will refuse to take the Thunderstone.

Using a stone
Growlithe	→ Fire Stone	Arcanine

Usually there are no special requirements for stone-induced evolution, with only two exceptions: Kirlia and Snorunt.

Kirlia
	→ Dawn Stone (male)	Gallade

Snorunt
	→ Dawn Stone (female)	Froslass

Note that sometimes the Oval Stone is said to be an evolutionary stone, because it is a stone and it is required for an evolution. However, technically Oval Stone is an evolution-inducing held item, which Happiny must be holding to evolve into Chansey when it levels up.

Evolution via trading

Main article: Trade

See also: Pokémon that evolve through trading

A few Pokémon evolve only when they are traded. The evolution starts immediately after the trade is completed, regardless of the method of trading used. However, sometimes there are additional conditions.

Trade
Haunter	→ Trade	Gengar

Holding a certain item

Main article: Evolution-inducing held item

See also: Pokémon that evolve by trading with a held item

Some Pokémon evolve when traded only if they are holding a certain item. Like any evolution-inducing held item, the item disappears after the Pokémon evolves.

Trade while holding an item
Electabuzz	→ Trade Holding an Electirizer	Electivire