Pokémon/Pokédex/Evolution

In the fictional Pokémon universe, evolution (進化, shinka) is the change in form of a Pokémon, usually accompanied by an increase in statistic values. It is closely analogous to metamorphosis—the Pokémon may gain or change its type.

The evolution of a Pokémon can be halted in the video game series by pressing the B button or by letting the Pokémon hold the Everstone item. However, in some cases, a Pokémon may refuse to evolve. This occurred in the anime with Ash's Pikachu, Bulbasaur, and Squirtle, who refused to evolve for an unknown reason.

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Evolution can occur in Pokémon for several different reasons. However, the five most common kinds of evolution are by leveling up, using a special stone, trading, the happiness of a Pokémon, and item evolutions.

A Pokémon’s overall strength is measured by its level, which ranges from 1 to 100. The most common cause of evolution is leveling up either by gaining experience points or by feeding a Pokémon Rare Candy, which instantly elevates the Pokémon by one level. A Pokémon that evolves in this manner will evolve once it reaches a certain level (e.g., Bulbasaur evolves into Ivysaur at level 16). Level-based evolution can be halted by the trainer at any time before the process is complete, by pressing the 'B' button. In general, the lower the evolutionary stage that the Pokémon is, the faster it will learn moves.

Another cause of evolution is exposure to an evolution stone. These stones all elementhave properties which affect specific Pokémon. The evolution stones include the Fire Stone, Water Stone, Thunder Stone, Leaf Stone, Moon Stone, Sun Stone, Dawn Stone, Shiny Stone, Dusk Stone, and the Oval Stone.

The stones, which are usually rare, are consumed in the process. There is the possibility of multiple evolutionary pathways triggered by stones, which is perhaps most notable in the Pokémon Eevee. A Normal-type, Eevee has seven possible evolutions, three of which, Vaporeon, Jolteon, and Flareon, are triggered by the Water, Thunder, and Fire stones, respectively. The Pokémon Gloom can evolve with either the Leaf Stone into Vileplume or the Sun Stone into Bellossom. Two Pokémon of certain gender evolve with the Dawn Stone: a male Kirlia into Gallade and a female Snorunt into Froslass.

In Pokémon Diamond and Pearl, stone evolution no longer occurs instantaneously when a Pokémon comes in contact with a stone. In most situations however, instantaneous evolution may occur, as with Growlithe to Arcanine. Holding the evolutionary stone is just another way of making it evolve.^[1]

The third type of evolution is trade evolution. In this case, Pokémon evolve after they are traded among players. This generally involves the connection of two game consoles and the trade of a Pokémon from one game to another.

Four Pokémon evolve immediately when traded: Kadabra evolves into Alakazam, Machoke into Machamp, Graveler into Golem, and Haunter into Gengar. This evolution cannot be stopped once started, but it can be prevented if the Pokémon is holding an Everstone* during trade.

Other Pokémon evolve by trade provided they are holding certain items. As with stone evolution, the item is consumed during evolution. Rhydon must be holding a Protector while being traded to evolve into Rhyperior. Magmar can evolve into Magmortar while holding a Magmarizer while trading and Electabuzz can evolve into Electivire while holding an Electrizer while trading. Onix and Scyther must hold a Metal Coat while being traded in order to evolve into Steelix and Scizor respectively. Poliwhirl and Slowpoke can evolve into Politoed and Slowking respectively if they are traded while holding a King’s Rock. Seadra can evolve into Kingdra while holding Dragon Scale, and Clamperl can evolve into Gorebyss or Huntail, depending on if it is holding a DeepSeaScale or DeepSeaTooth when it is traded. Dusclops can evolve into Dusknoir while holding Reaper Cloth during trade. Only one Pokémon evolves twice through trade: Porygon, when traded while holding the Up-Grade becomes Porygon2, and Porygon2, when traded with the Dubious Disc, evolves into Porygon-Z.

Since Pokémon Gold, Silver, and Crystal, the games track a hidden statistic measuring a Pokémon’s contentedness. It changes based on several factors, such as how often a Pokémon is defeated in battle or if it has been fed stat-enhancing items. A player can gauge a Pokémon’s general happiness level by taking it to certain NPCs, or using Pokémon Stadium 2 or Pokémon Box to monitor the strength of its friendship with the trainer. If this statistic is at a high level, a Pokémon that evolves in this manner will evolve upon gaining another level. Usually, the baby forms of Pokémon, such as Pichu, Cleffa, Togepi, and Igglybuff, evolve in this way. Some older Pokémon, such as Chansey and Golbat, were given new evolutions through this method: Blissey and Crobat, respectively.

In some cases, this evolution will only occur at a particular time of day; for instance, a happy Eevee evolves into the Dark-type Umbreon only when it levels up at night, and the Psychic-type Espeon during only the daytime. Likewise Budew will evolve into Roselia when it is happy and levels up during the day and Riolu will evolve into Lucario only when it is happy and levels up at day also . Chingling evolves into Chimecho when it is happy and levels up at night.

There are several variations on level-based evolution unique to individual Pokémon.

Statistics-based evolution

In comparison, Tyrogue is a Baby Pokémon guaranteed evolution at level 20, and can become one of three different Pokémon as a result. However, Tyrogue's evolution can be influenced towards either of the three forms by the trainer. This is accomplished by careful management of the two factors which govern Tyrogue's evolution: its Attack and Defense statistic values. If the value of Tyrogue's Defense statistic is greater than that of its Attack statistic, Tyrogue will evolve into Hitmonchan; if the value of its Attack statistic exceeds that of its Defense, Tyrogue will evolve into Hitmonlee; if both values are equal, it will evolve into Hitmontop. Another would be Feebas that evolves into Milotic regardless of its level or moveset, but only with a completely maximized Beauty statistic (then level up), a value normally independent from evolution and used only in Pokémon Contests.

Location-based Evolution

Certain Pokémon evolve if their levels increase at all, regardless of the level attained, but only if the Pokémon gains that level in a specific area. Such Pokémon include two evolutions of Eevee, Leafeon and Glaceon. They evolve if a level is obtained by the Eevee near the Moss Rock and Ice Rock in Sinnoh, respectively. By comparison, Magneton and Nosepass can evolve into Magnezone and Probopass respectively if they level up in Sinnoh's Mt. Coronet. (This leads to the problem of how pokemon will evolve in future regions)

Gender-based evolution

Two Bug-type Pokémon evolve per level-based evolution as normal, but only if they are of a certain gender: Combee evolves into a Vespiquen at level 21, but only if the Combee is female since male Combee never evolve. Burmy evolves at level 20 into a Mothim if it is male, or a Wormadam if it is female.

Party-based evolution

Another unique variation of level-based evolution in which a trainer's party composition might come into play is demonstrated by the Nincada evolutionary family. When Nincada evolves into Ninjask at level 20, the trainer will also receive Shedinja if there is an empty space in the player's party. Mantyke will evolve into Mantine only if a Remoraid is present in the trainer's party.

Move-based evolution

Other evolutions may require Pokémon to have leveled up while they know a certain move, such as a Lickitung knowing Rollout, or an Aipom knowing Double Hit. Several Pokémon evolve after learning Ancientpower, including Piloswine, Tangela,Yanma. Bonsly, and Mime.Jr. will evolve if they know the move mimic.

Item-based evolution

In contrast, some require the Pokémon to hold a specific item during a level up. In addition, the Pokémon might need to be holding the item at a certain time of day - Sneasel’s evolution into Weavile and Gligar into Gliscor for example.

Because evolution is such an integral part of the Pokémon concept, it appears not just in the main Pokémon role-playing games, but also in other media.

Evolution in the anime follows slightly different rules at times. One notable change is that Pokémon often evolve in the middle of a battle, which cannot happen in the games. The anime featured an incident wherein Ash’s Pikachu preferred not to evolve. This was first seen in the Pokémon Yellow version. Also in Pokémon Yellow, the player’s starting Pikachu refuses to evolve.

Usually in the anime, a Pokémon would evolve by glowing as a white silhouette, changing shape, and then the glow would fade to reveal its new form. However, there were a few exceptions; Ash's Caterpie evolved into Metapod by shooting string on itself and shedding its skin. Then Metapod would evolve into Butterfree by flashing, and the butterfly Pokémon would emerge from the shell, like a real butterfly coming out of pupation. Beedrill and its pre-evolved forms would also follow this practice. Eventually later in the series, these Pokémon types would evolve the normal way how other Pokémon do: by glowing and changing shape. Also, when Poliwag would evolve into Poliwhirl, it would stop changing shape halfway and appear as a spinning circle of light before resuming its evolution to its next form. This is not present in its evolution into Poliwrath, but it does appear as a rotating circle of light when evolving into Politoed. Also, in The Flame Pokemon-athon, while Ponyta was evolving to Rapidash to win the race, its white silhuoette while evolving was also in a rainbow-ish color.

Another instance is the Pokémon Trading Card Game, which allows evolution of the player’s creatures by playing the correct card on top of the original Pokémon. Evolution is usually a strategic necessity, as the evolved Pokémon are more powerful and may be able to take advantage of tools and circumstances that Basic Pokémon cannot.

In Pokémon Pinball and its sequel, Pokémon Pinball: Ruby & Sapphire, the player must accomplish certain tasks to enter “EVO mode”, and may then evolve any Pokémon caught in that round of play by using the ball to collect a set of three icons, representing experience, appropriate evolution stones, hearts for friendship, link cables for trade, etc., scattered around the board, representing the method by which it evolves, before time runs out.

In Pokémon Mystery Dungeon, the world of Pokemon is plagued by natural disasters, including the inability of all native Pokémon to evolve. Once the player’s team has defeated Rayquaza, the Luminous Cave, where evolution can occur, appears at Whiscash Pond. Evolution in Mystery Dungeon requires the same conditions (levels, stones, etc.) as in the main RPGs, except that happiness evolution instead occurs only if the Pokémon’s IQ is high enough, and Pokémon which evolve through trading must use a Link Cable item in addition to any other required item. Eevee will evolve into Espeon or Umbreon with a high enough IQ by using the Solar or Lunar Ribbons, and Feebas will evolve with the Beauty Scarf. Shedinja appears automatically after Nincada evolves. Wurmple will evolve into either Silcoon or Cascoon depending on its personality value at level 7.