Evolution

Ivysaur becomes Venusaur, depicted in Pokémon FireRed and LeafGreen.

During the course of a Pokémon's development, under certain circumstances specific to that Pokémon's species, it may evolve (Japanese: 進化 shinka) into a different Pokémon. This change is not merely physical, however, as Pokémon of a higher evolutionary stage have different (and usually more powerful) base stats than their predecessors, may have different moves that can be learned, and sometimes change their types, though usually at least one of the types of the previous form is preserved. Other statistics, such as nature and EVs, as well as alternate coloration, are preserved.

Evolution families

An evolution family is a group of Pokémon who will all, if bred with Ditto, make a Pokémon egg that will hatch into the same Pokémon, excluding baby Pokémon. This also means that the most basic form has the potential to become any of the rest of the family, although it will only be able to follow one evolutionary path, ultimately.

Stages of evolution

Pokémon can be classed into different evolutionary stages, based on their appearance in their evolution family. All Pokémon fall into one of four groups: baby Pokémon, unevolved Pokémon, first-evolution Pokémon, and second-evolution Pokémon. These groups are also the basis for the TCG's grouping of Baby Pokémon, Basic Pokémon, Stage 1 Pokémon, and Stage 2 Pokémon, respectively.

Due to the fact that no evolution family contains both a baby Pokémon and a second-evolution Pokémon, many regard baby Pokémon as the most basic form, while moving their evolved counterparts one level higher. For example, originally, Pikachu was regarded as an unevolved Pokémon, however, with the release of Pichu in Generation II, many now considered it more on par with Pokémon like Charmeleon, though its TCG classification remained the same.

Two-evolution families

Main article: Pokémon that are part of a three-stage evolutionary line

Perhaps the most well-known types of evolution families are those that feature two separate evolutionary events in the Pokémon's development. Indeed, this type of evolution family is what all of the starter Pokémon in the main series are a part of, including Pikachu. An example of this type of evolution family is below.

Lowest	Trigger	Middle	Trigger	Highest
Dratini	Level 30	Dragonair	Level 55	Dragonite

One-evolution families

Main article: Pokémon that are part of a two-stage evolutionary line

By far the most common type of evolution family, these families are based in a Pokémon that will only ever evolve once in its development. About one third of all Pokémon that would later get a baby form were part of this kind of evolution family before their baby form was revealed. An example of this type of evolution family is below.

Lowest	Trigger	Highest
Scyther	Trade holding Metal Coat	Scizor

Pokémon that do not evolve

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

The least common type of evolution family, of course, is that in which no evolutionary event takes place, meaning that it is made up of only one member. Many of the Pokémon that have no evolutionary event are, of course, legendary Pokémon. However, there are still 42 other Pokémon that do not evolve. Below is a list of all non-legendary Pokémon that do not evolve.

Gen I		Gen II		Gen III		Gen IV
	Farfetch'd		Unown		Sableye		Pachirisu
	Kangaskhan		Girafarig		Mawile		Chatot
	Pinsir		Dunsparce		Plusle		Spiritomb
	Tauros		Qwilfish		Minun		Carnivine
	Lapras		Shuckle		Volbeat		Rotom
	Ditto		Heracross		Illumise
	Aerodactyl		Corsola		Torkoal
			Delibird		Spinda
			Skarmory		Zangoose
			Stantler		Seviper
			Smeargle		Lunatone
			Miltank		Solrock
					Castform
					Kecleon
					Tropius
					Absol
					Relicanth
					Luvdisc

It must be noted that not belonging to an evolutionary family is not an indication of strength overall. Some Pokémon, like Lapras and Heracross are comparable to fully evolved Pokémon while others, like Luvdisc and Pachirisu, are more comparable to unevolved Pokémon. Often this indicates a Pokémon's possibility to be eligible for future new evolutions or pre-evolutions.

Branch evolution families

Main article: List of Pokémon with branched evolutions

Several families, while also one- and two-evolution families, are also branch evolution families. What this means is that there is a split in the evolutionary line at some point so that even though two Pokémon of the same species evolve the same amount of times, they can become one of two or more entirely different creatures. Eevee is the best-known example of this, evolving seven different ways depending on the method used. An example of this type of evolution family is below.

Lowest	Trigger	Middle	Trigger	Highest
Poliwag	Level 25	Poliwhirl	Water Stone	Poliwrath
			Trade holding King's Rock	Politoed

Advantages

A major difference between the final forms of an evolution family with a branch in evolution is in the way that their base stats line up. For example, Kirlia evolves into both Gardevoir and Gallade, which both have 518 total base stats. However, Gallade's base stat in Attack is 125 and its base stat in Special Attack is 65. The reverse is true for Gardevoir, whose Special Attack is 125 and whose Attack is 65. This is true of many opposing evolutions, with one focusing in one specific stat, the other focusing in a separate stat, and both having the same total stats. This is especially obvious in the Eeveelutions, who each have exactly the same base stats, though organized differently.

A listing of the stat focuses is below.

Basic form		Evolutions		Types		Difference
	Oddish		Vileplume			Special Attack is 100, Special Defense is 90
			Bellossom			Special Defense is 100, Special Attack is 90
	Poliwag		Poliwrath			Attack is 20 higher, Defense is 10 higher
			Politoed			Special Defense is 20 higher, Special Attack is 10 higher
	Slowpoke		Slowbro			Defense is 110, Special Defense is 80
			Slowking			Special Defense is 110, Defense is 80
	Eevee		Vaporeon			Highest stat is HP
			Jolteon			Highest stat is Speed
			Flareon			Highest stat is Attack
			Espeon			Highest stat is Special Attack
			Umbreon			Highest stat is Special Defense
			Leafeon			Highest stat is Defense
			Glaceon			Highest stat is Special Attack
	Tyrogue		Hitmonlee			Large difference between Attack and Defense
			Hitmonchan			Speed lower than Defense, Attack and Defense more equal
			Hitmontop			Attack and Defense equal, Speed at minimum
	Wurmple		Beautifly			Attack and Special Attack higher than Defense and Special Defense
			Dustox			Defense and Special Defense higher than Attack and Special Attack
	Ralts		Gardevoir			Special Attack is 125, Attack is 65
			Gallade			Attack is 125, Special Attack is 65
	Snorunt		Glalie			All stats are 80
			Froslass			HP, Defense, Special Defense each 10 lower, Speed 30 higher
	Clamperl		Huntail			Attack is 104, Special Attack is 94
			Gorebyss			Attack is 84, Special Attack is 114
	Burmy		Wormadam			Focus in Defense
			Wormadam			Focus in Special Defense
			Wormadam			Equal Defenses
			Mothim			Focus in Attack, Special Attack, and Speed

Methods of evolution

Main article: Methods of evolution

The various triggers for a Pokémon's evolution are almost as varied as the Pokémon themselves. The most common of them is evolution by leveling up at or above a certain level. Others include leveling up when happiness has reached a high level, when the Pokémon is traded, when the Pokémon is traded holding an item, leveled up holding an item, or even has an evolutionary stone used on it.

Most commonly, Pokémon that can evolve into more than one Pokémon will have the ways in which the evolution is activated being slightly similar, such as having both be by evolutionary stone or by holding an item and trading. Closely-related Pokémon, such as Nidoran♀ and Nidoran♂, will also have very similar, if not identical, evolution methods.

In the anime

In the anime, evolution happens in much the same way as it does in the games; though level-based evolution nor trade-based evolutions do not occur using those methods, there are similarities in the way they come about. For example, Misty's Poliwhirl evolved into Politoed because it found Ash's King's Rock and was holding it when Misty sent it out, while in the games it is required that Poliwhirl be traded while holding the King's Rock for the evolution to take place.

Additionally, a difference can be noted in the fact that Pokémon evolve during a battle, as opposed to after it. There are also several instances of an evolutionary trigger being incorrect, such as March of the Exeggutor Squad where several Exeggcute evolve into Exeggutor without the aid of a Leaf Stone. Pokémon may also evolve when they are needed to, for an extra boost of power, instead of after a set amount of training, such as when Ash's Charmeleon evolved into Charizard.

For a list of all evolutions that Pokémon belonging to the main cast have undergone, see List of anime Pokémon by evolution.

In the TCG

Main article: Evolution (TCG)

Evolution in the TCG functions similarly in many aspects to that of the games, however, there is no different requirement that needs to be met depending on the Pokémon species to be evolved to move on to the next stage.

In relation to the real world

Evolution in Pokémon, for most species, is more akin to metamorphosis than to actual evolution. The Pokémon whose evolution is closest to the real-world definition of evolution is Eevee, whose cellular structure changes due to its environment.