From Bulbapedia, the community-driven Pokmon encyclopedia.

Evolution (Japanese: evolution) is a process in which a Pokmon changes into a different species of Pokmon. This change is not merely physical, however, as Pokmon 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 shininess, are preserved. With respect to real-world phenomena, Pokmon Evolution is more similar to metamorphosis than evolution. Evolution also appears to be a mostly independent phenomena from the aging process for most species, though Baby Pokmon need to evolve to their next stage in order to breed.

Professor Elm and Professor Rowan are the leading experts in Pokmon Evolution. According to the latter's research, over 90% of all Pokmon are connected to at least one other through Evolution (this is true only if Legendary Pokmon are excluded.) Rowan is currently investigating whether Evolution is a form of maturity in Pokmon, and looking at the implications this process has on Legendary Pokmon, which don't evolve.

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

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

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

By far the most common type of evolution family, these families are based in a Pokmon that will only ever evolve once in its development. About one third of all Pokmon 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.

Perhaps the most well-known types of evolution families are those that feature two separate evolutionary events in the Pokmon's development. Indeed, this type of evolution family is what all of the starter Pokmon in the core series are a part of (excluding the starter Pikachu in Pokmon Yellow, as Pichu did not yet exist and it could not be evolved into Raichu; and Eevee, which could only be taken by Blue), as well as all pseudo-legendary Pokmon. An example of this type of evolution family is below.

The least common type of evolution family is that in which no evolutionary event takes place, meaning that it is made up of only one member. Many of the Pokmon that have no evolutionary relatives are Legendary and Mythical Pokmon. However, there are still 75 other Pokmon that do not evolve.

Not belonging to an evolutionary family is not indicative of strength, or a lack thereof. Some Pokmon, such as Heracross and Skarmory, are comparable to fully evolved Pokmon while others, like Delibird and Luvdisc, are more comparable to unevolved Pokmon. Often this indicates a Pokmon's possibility to be eligible for future new evolutions or pre-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 Pokmon 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 eight different ways depending on the method used. An example of this type of evolution family is below.

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 can evolve 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.

The various triggers for a Pokmon's evolution are almost as varied as the Pokmon themselves, and some Pokmon have a unique evolution method. The most common of them is Evolution by leveling up at or above a certain level. Other methods include the following:

Additionally, holding an Everstone prevents a Pokmon from evolving, as well as surprising a Pokmon via the B Button. The latter method is known as an "Evolution cancel".

Pokmon that get knocked out during a battle will evolve at the end of that battle if its requirements have been met. However, before Generation VI, losing a battle would make Pokmon not evolve even if the conditions have been met.

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

Some Pokmon have different evolutions depending on their gender. For example, only female Combee can evolve into Vespiquen; male Combee cannot evolve at all. Meanwhile, all Snorunt can evolve into Glalie, but females ones have the option of evolving into Froslass instead. This instance occurs in a similar way with Kirlia, albeit with males having split evolution instead.

Also, there have been situations in which the current party must be configured in a specific manner for some Pokmon to evolve. So far, only three Pokmon need to have these special requirements. Mantyke will evolve into Mantine if leveled up with a Remoraid in the player's party. Nincada will evolve into Ninjask when it reaches level 20. However, if there happens to be an empty space in the player's party (and a spare Pok Ball in Generation IV onward), a Shedinja will also appear in the party. Pancham evolves into Pangoro if its level is 32 or higher and there is a Dark-type Pokmon in the player's party.

Some Pokmon evolve in other unique ways. If one trades a Karrablast for a Shelmet, they will evolve into Escavalier and Accelgor, respectively, though neither will evolve if one of them holds an Everstone. When Inkay reaches level 30, the player must hold the 3DS upside-down for it to evolve into Malamar. Also introduced was a weather-based evolution: Sliggoo will evolve into Goodra beginning at level 50 only if it is raining in the area that the player is in. Finally, Sylveon can only be obtained by leveling up an Eevee that knows any Fairy-type moves and has at least two hearts of affection in Pokmon-Amie or Pokmon Refresh.

Some missions Hey You, Pikachu! involve Pikachu interacting with other Pokmon in certain ways to cause their evolution. In Caring for Caterpie, the player and Pikachu supervise a group of Caterpie, who will evolve into Metapod and then Butterfree if treated well. In Field Trip, Pikachu can water wild Oddish and Gloom, causing them to evolve into Gloom and Vileplume, respectively.

In Pokmon Colosseum and XD: Gale of Darkness, while evolution typically works as normal in the main series, Shadow Pokmon are incapable of evolving until they are purified and return to normal. In Pokmon XD: Gale of Dakrness, the player's Eevee is incapable of evolving into Espeon or Umbreon through normal methods, because the game does not have a Time mechanic. However, early in the game, the player is given their choice of evolution item to evolve it, including the Sun and Moon Shards, Key Items that will evolve Eevee into Espeon or Umbreon respectively after it levels up.

In Pokmon Conquest, because the mechanics of levels, experience, and friendship do not exist, Pokmon typically evolve once they reach a certain link threshold with their partnered Warrior or Warlord. Pokmon that normally evolve via high friendship in the main series games, such as Golbat, instead evolve after reaching a certain link percentage, usually between 60 and 70 percent. Pokmon that normally evolve at a set level instead evolve when a certain stat reaches a specific value. For example, Spheal evolves when its HP has reached a value of 138, which is partially determined by the link with its Warrior. Warriors with Pokmon that require an evolutionary stone to evolve must equip themselves with that item and then perform an action that causes their link to improve, such as completing a battle.

In Pokmon Pinball and Pokmon Pinball: Ruby & Sapphire, the player can evolve Pokmon they caught in Catch 'Em Mode in a separate mode called Evolution Mode (EVO Mode in Pinball RS). In this mode the player selects an evolution-capable Pokmon in their possession, then guide their ball towards three symbols representative of their method of evolution in the main games, such as EX for Level evolution, or a Link Cable for Trade evolution. If the player collects the three symbols in time, they can bring their ball to the Center Hole to evolve their Pokmon, awarding them with their Pokdex entry and points.

In the Mystery Dungeon series, evolution is restricted until reaching the location where evolution is taking place. Evolution is typically done in a ritual held in several locations across the Pokmon world, including Luminous Cave, the Luminous Spring, or the Tree of Life. However, starting in Explorers of Time and Explorers of Darkness, the player character and their partner may not evolve until they complete an additional scenario. Pokmon who evolve through unusual methods require an additional item to act as a catalyst.

In Pokmon Mystery Dungeon: Gates to Infinity forward, enemy Pokmon may evolve after defeating a member of the player's party. In Super Mystery Dungeon, the player character and their partner evolve into their final forms several times throughout the story. In addition, connectable Pokmon that exist as NPCs in this game or previous games will refuse evolution. However, because all Pokmon can be recruited separately though the Connection Orb, the player can still access their respective evolved forms in alternate ways.

In Pokmon Snap, the player can interact with Pokmon in certain ways that will make them evolve.

In Pokmon GO, the player can evolve Pokmon by spending Candy. The Candy cost for evolution varies between Pokmon species, ranging from 12 (to evolve Caterpie into Metapod) to 400 (to evolve Magikarp into Gyarados).

Each evolutionary family has their own kind of Candy. Candy can be obtained by catching or hatching Pokmon of that evolutionary family. The player can also obtain 1 Candy for its evolutionary family by permanently transferring it to Professor Willow.

The form Eevee normally evolves into seems to be random. However, the player can nickname their Eevee after one of the Eevee brothers in order to guarantee what the end result of the evolution will be.

In the anime, Evolution happens in much the same way as it does in the games; though level-based evolutions and 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 (It should be noted that Poliwhirl had been through a machine in connection with it being healed at the Pokmon Center, while holding the item). When a Beedrill attacked Ash's Metapod, it caused a crack to appear on its shell, which Butterfree came out of.

Additionally, a difference can be seen in the fact that Pokmon evolve during a battle, as opposed to after it. Pokmon may also evolve when they are needed to, for an extra boost of power or gaining new abilities, instead of after a set amount of training, such as when Ash's Charmeleon evolved into Charizard. In addition, Pokmon can sometimes choose not to evolve, even if they evolve by a 'natural' method such as leveling up. This was shown when Ash's Bulbasaur refused to evolve during an evolution festival for all Bulbasaur to evolve in Bulbasaur's Mysterious Garden. It appears that Evolution has emotional implications for Pokmon - some Pokmon, such as Team Rocket's Meowth, dislike their evolved forms, while others such as Ash's Pikachu simply want to prove they can be powerful without evolving. Conversely, when Pokmon do evolve, this can often be linked with an experience that causes them to mature emotionally or deal with an emotional issue, such as when the Poochyena in A Bite to Remember evolved, or the Paras in The Problem With Paras. Poochyena, for some reason, had an aversion to using the move Bite, while Paras was extremely timid and weak in battle. Both of them evolved shortly after overcoming these issues.

When a Pokmon begins to evolve, it will be enveloped by a brightly-colored light while slowly changing form; in the Original, Advanced, and Diamond&Pearl series, the light is simply white in color while in the Black and White and XY series, the light is blue in color.

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

Evolution in the Pokmon Trading Card Game is very similar in some aspects to its counterpart in the core series. However, it differs mostly in the fact that there are no different methods needed to evolve a Pokmon, but instead, all Pokmon evolve simply by placing the next stage on top of a Pokmon in play that it evolves into.

Pokmon cannot be evolved on the first turn of the game or on the first turn they come into play. They also cannot be evolved if on the same turn they were previously evolved or devolved.

There are four different stages of evolution in the TCG, Baby Pokmon, Basic Pokmon, Stage 1 Pokmon, and Stage 2 Pokmon. Of these, only Baby and Basic Pokmon may be placed onto the Bench during the setup phase and during play; Stage 1 and Stage 2 Pokmon are considered to be evolution cards and therefore unable to be played except on top of their corresponding pre-evolved forms. The stage of evolution is indicated in a conspicuous place on each and every Pokmon card, though the placement differs among the four generations of cards.

Within the deck and discard pile, only Stage 1 and Stage 2 cards are considered to be "evolution cards" for the purpose of a Trainer card or Pokmon Power which allows them to be searched for. In play, a Basic Pokmon card can be considered an evolution card if it is evolved from its Baby stage.

A Baby Pokmon is much the same in the TCG as it is in the core series of games. In fact, as with baby Pokmon released beyond Generation II, it is not even necessary for a Pokmon to even go through this stage of their evolutionary line, as the Pokmon can just start from their basic form. Baby Pokmon are among the weakest in the TCG, most often having 30 HP, as well as one of two special Pok-Bodys: one prevents all damage done to the Baby Pokmon while it is Asleep (Baby Pokmon with this Pok-Body also usually have an attack that changes their status to Asleep), and the other forces a Pokmon attempting to attack the Baby Pokmon to flip a coin, the attack doing nothing if that coin ends up tails.

A Basic Pokmon is the most basic of Pokmon cards, as can be deduced from its name. Commonly basic Pokmon will have low HP, a common rarity, and low damage and Energy costs. These cards can be placed directly into play without another Pokmon card needing to be in play first. Pokmon that evolve from a Pokmon released in a later generation, such as Electabuzz or Pikachu, always are basic Pokmon, despite being the second Pokmon in their own evolutionary lines. Baby Pokmon, Shining Pokmon, Pokmon , Pokemon SP, and Pokmon-EX are always Basic, and the latter four cannot evolve.

A Stage 1 Pokmon are the first kind of evolution card, being able to be evolved from a Basic Pokmon. Stage 1 cards are most commonly uncommon in rarity. Stage 1 Pokmon are also able to be Dark Pokmon and Light Pokmon.

A Stage 2 Pokmon is the highest of evolution cards, commonly rare or holographic in rarity, and can only, in normal conditions, be evolved from a Stage 1 Pokmon. Stage 2 Pokmon are also able to be Dark Pokmon and Light Pokmon.

M Pokmon-EX cards were introduced in XY expansion and introduce the Mega Evolution mechanic featured in Pokmon X and Y. They are identified by a stylized graphic on the card name. M Pokmon-EX can only be played by Mega Evolving from basic Pokmon-EX. Doing so ends a players Turn immediately. Other than this, M Pokmon-EX share the same rules and design as regular Pokmon-EX and evolving Pokmon, with the addition of boosted Hit Points and more powerful Attacks.

A Pokmon card that is in the player's hand must say specifically that it evolves from a Pokmon card that is in play on the player's side. For example, Dark Blastoise states on the card "Evolves from Dark Wartortle". This means that any card named Dark Wartortle may be evolved into Dark Blastoise. However, a card simply named Wartortle cannot. Likewise, Pokmon such as Rhyhorn cannot be evolved into a Pokmon that says on it "Evolves from Team Magma's Rhyhorn".

However, Pokmon cards from different sets may evolve into one another. For example, Dark Crobat can evolve from either Dark Golbat of the Team Rocket set or Dark Golbat of the EX Team Rocket Returns set. So long as the card names match precisely both to (here Dark Crobat) and from (here Dark Golbat), the evolution is legal. This rule, of course, can be circumvented by certain means, such as Pokmon Powers and Trainer cards, however, this is not common.

Evolution in Pokmon, for most species, is more akin to metamorphosis than to actual evolution. This is because real life evolution happens to a population rather than to individuals, and happens over much larger time scales than in the Pokmon world. In the Pokmon Adventures manga, it is mentioned that Pokmon Evolution is an entirely separate phenomenon from the normal process of evolution, and is a mysterious ability exclusive to Pokmon that is still not fully understood. In Pokmon Super Mystery Dungeon, it is described in the health class at the school in Serene Village as when a Pokmon's body rapidly grows larger with many other changes bringing a Pokmon closer to being an adult, being described akin to puberty.

Link:

Evolution - Bulbapedia, the community-driven Pokmon encyclopedia