Evolution

**Evolution** is a process in which a Pokémon changes into a different species of Pokémon.

With respect to real-world phenomena, Pokémon evolution is more similar to metamorphosis than evolution. Evolution is mostly independent from the aging process, instead being triggered by external factors, such as gaining experience in battle or being exposed to certain items.

Evolution is not a merely visual change, as Pokémon of a higher evolutionary stage have different (and usually increased) stats, can learn different moves, and sometimes change types (although normally at least one of the pre-evolved form's types remains the same). Pokémon may also change Ability upon evolution.

Professor Elm and Professor Rowan are the leading experts in Pokémon evolution. According to Elm's research, over 90% of all Pokémon are connected to at least one other through evolution. (Currently, the actual percentage is 94%.) Rowan's research focuses on whether evolution is a form of maturity in Pokémon, and looking at the implications of the process on Legendary Pokémon (most of which cannot evolve).

## Evolutionary families

An evolution family is a group of Pokémon who are all related by evolution. The species at the lowest evolutionary stage in an evolutionary family can ultimately evolve into any member of the evolutionary family.

### Evolutionary stages

Pokémon evolutionary families have anywhere between one and three stages. In a one-stage family, there is only a single Pokémon that cannot evolve. In a two-stage family, any member of the family can evolve at most once, from the unevolved form into one of the evolved forms. In a three-stage family, at least one of the evolved forms can evolve once again.

#### One-evolution families

*See also: Category:Pokémon that are part of a two-stage evolutionary line*

These are evolutionary families in which a Pokémon can only ever evolve once. These are the most common type of evolutionary families. An example of this type of evolution family is below.

#### Two-evolution families

*See also: Category:Pokémon that are part of a three-stage evolutionary line*

These are evolutionary families in which a Pokémon can evolve twice. All starter Pokémon have this type of evolutionary family. An example of this type of evolution family is below.

#### Pokémon that do not evolve

*Main article: List of Pokémon that are not part of an evolutionary line*

These are evolutionary families with a single member, which cannot evolve. Many of the Pokémon that have no evolutionary relatives are Legendary or Mythical Pokémon, although there are some Legendary and Mythical Pokémon that can evolve.

#### Branched evolution families

*Main article: List of Pokémon with branched evolutions*

Several one- and two-evolution families are also branched evolution families. A branched evolution family has a member that can evolve into one of several different Pokémon. Eevee is the most extreme example, having eight different possible evolved forms. An example of this type of evolution family is below.

## Methods of evolution

*Main article: Methods of evolution*

In the game, Pokémon normally only evolve after one of two events:

* Gaining a level (the most common trigger)
* Being exposed to an item (such as an Evolution stone)

In addition to the trigger, many Pokémon have one or more additional requirements for them to be able to evolve. These include:

* Having high friendship
* Holding a specific item
* The time of day
* Knowing a certain move or a move of a certain type
* The location the player is in, or the current weather in that location
* Having a certain Pokémon in the party, or a certain type of Pokémon

Some evolutions are dependent on the Pokémon's gender. For example, only female Combee can evolve into Vespiquen—male Combee cannot evolve at all. Similarly, all Snorunt can evolve into Glalie, but only female Snorunt can evolve into Froslass. On the other hand, male Burmy can only evolve into Mothim, while female Burmy can only evolve into Wormadam.

For some evolutions into Pokémon with multiple forms, the form of the evolved Pokémon depends on how it evolved. For example, Wormadam's cloak depends on the cloak Burmy had when it evolved.

## In the game

When a Pokémon evolves, it becomes a new species of Pokémon. This new species has a different Pokédex number and base stats, and may be a different type, learn different moves, and have a different Ability. The Pokémon's personal properties, however, such as Nature and Shininess, remain.

Holding an Everstone prevents a Pokémon from evolving by level up. Additionally, the player can prevent a Pokémon from evolving upon leveling up by pressing the "Back" button when it would evolve.

When a Pokémon evolves, it immediately attempts to learn all moves that the evolved form can learn at its current level. Additionally, some Pokémon have Evolution moves, which are moves that Pokémon will always attempt to learn when evolving into that species, regardless of level.

### Abilities

Normally, a Pokémon will retain its Ability slot upon evolution - if it had its species second Ability before evolving, it will still have its species second Ability after evolving (e.g. a Poochyena with Quick Feet will still have Quick Feet after evolving into Mightyena, but Poochyena with Run Away will instead have Intimidate after evolving.).

## Trivia

* Of all non-Legendary and non-Mythical Pokémon, 90.87% are part of an evolutionary line.
	+ Counting Legendary and Mythical Pokémon, 84.19% of all Pokémon are part of an evolutionary line.
* Out of all Pokémon that evolve by leveling up, Larvesta evolves later than any other unevolved Pokémon, starting at level 59.
* Of all the Pokémon that evolve by leveling up, Hydreigon evolves from its pre-evolution later than any other Pokémon, starting at level 64.
* Hoenn introduced the most non-Legendary and non-Mythical Pokémon that do not evolve, with 18.
	+ Sinnoh and Unova are tied for the fewest, with just five each.