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Evolution is the term given to the change of appearance in a chao.


The first evolution is what most people refer to when using the term evolution on it's own. At this point, a baby Chao goes into a Cocoon and emerges as an adult. The evolution marks the Chao becoming able to mate, and a permanent change in appearance, locking it into its Alignment and evolution type, until Reincarnation. This page focuses on the First Evolution for the most part.

There is another evolution known as the Gradual Evolution, which occurs over time rather than in a single moment like the first evolution. This is the Chao changing appearance when approaching their first evolution or their Reincarnation. This evolution can be changed and influenced with the use of Small Animals and Chaos Drives. Gradual Evolution often refers to the Second Evolution as it is the more significant of the 2 gradual changes.

First Evolution

When a Chao evolves, it becomes one of three alignments, Hero, Neutral, or Dark, and one of five ability types, Swim, Fly, Run, Power, and None. This provides 15 total First Evolutions. First Evolutions are named as Alignment/Ability Type, such as Neutral/Swim or Dark/Run.

The First Evolution process increases the Chao's grade by one letter rank for the ability type the Chao became, with Normal-type and Chaos Chao Evolutions increasing the Stamina grade. One of the two sets of the Chao's DNA will also gain the new rank.

The first instance of evolving a Hero aligned or Dark aligned Chao, in Sonic Adventure 2, also opens up the Hero Garden and Dark Garden, respectively. Hero and Dark aligned Chao are also a requirement to unlock Hero Races and Dark Races.

Stat Influence

It is very commonly believed that a Chao evolves into the Swim, Fly, Run, or Power types if the corresponding stat is the highest, and that the Normal type is based on Stamina or a balance between the other four stats. However this is not the case, and instead it is based on stat sliders that determine stat 'influence'. For example, you may have a Chao which is level 99 in the Fly stat and level 5 in all other stats. This does not ascertain that it will evolve into the Fly type.

The First Evolution of a Chao is determined by the Alignment slider and Stat sliders at the time the Chao enters its cocoon. The ability type of a Chao after evolution is determined by only its Stat sliders. These are two values for a Chao, separated into the Swim↔Fly slider and the Run↔Power slider. These sliders are hidden numbers for a Chao ranging from -1 to 1, where -1 represents Swim and Run for their sliders, and +1 represents Fly and Power. A Chao is born at 0 in both sliders. Receiving an animal causes the related slider to move by 0.1 in the related direction, while a Chaos Drive moves it by 0.05. Blue, Black, and Gold group animals move a random slider in a random direction by 0.1, so care must be taken when using them if there is a desired evolution path. Adult Chao receive half the amount of influence for both Chaos Drives and Animals, receiving 0.025 and 0.05 respectively per item. For child Chao at 0 influence, it takes 10 animals of one type or 20 Chaos Drives of one colour to maximise Stat Influence in one of the sliders. At 0 influence an adult Chao will need 20 animals or 40 Chaos Drives of one type to reach the maximum influence of -1 or +1.

The ability type of the evolved Chao is determined by the following rules, at the moment of evolution:

  • If a Chao's Swim↔Fly slider has a value ≤ -0.5, and the Run↔Power slider is close to 0, the Chao will become a Swim type Chao.
  • If a Chao's Run↔Power slider has a value ≤ -0.5, and the Swim↔Fly slider is close to 0, the Chao will become a Run type Chao.
  • If a Chao's Run↔Power slider has a value ≥ +0.5, and the Swim↔Fly slider is close to 0, the Chao will become a Power type Chao.
  • If a Chao's Swim↔Fly slider has a value ≥ +0.5, and the Run↔Power slider is close to 0, the Chao will become a Fly type Chao.
  • If a Chao's Swim↔Fly and Run↔Power sliders are both between -0.5 and +0.5, the Chao will become a Normal type Chao, or if special conditions are met the Chao will become a Chaos Chao.

In the rare case when a Chao's Swim↔Fly and Run↔Power sliders have equal absolute values, there is an order of which takes precedence:

  • The Swim type takes precedence over Run or Power types.
  • The Run and Power types take precedence over the Fly type.
  • The Fly type takes precedence over the Normal type.

By this principle, if a Chao has equally strong Swim and Power influence, -0.7 and +0.7 on both sliders, the Chao will evolve into a Swim type Chao. But if the Chao has -0.7 for Swim and +0.8 for Power, it will become a Power type Chao. This method also makes Normal and Chaos Chao lowest priority to obtain, as the Chao must be balanced in all directions to ensure the proper evolution.

Since Swim↔Fly work as one value and Run↔Power also operate as a single value, this means Swim influence and Fly influence can cancel each other out, while Power influence and Run influence cancel each other out.

If a Chao has maximised its Fly influence with +1 while also having -1 for Run, the Chao will evolve into a Run type. If you want to make sure your Chao becomes a Fly type, you will need to reduce the Run influence by giving some Power, as this will cancel out the Run's influence.

Alignment Influence

The alignment of the evolved Chao is decided by a hidden alignment slider, a value ranging from -1, representing Dark, to +1, representing Hero. A Chao is born at 0, representing neutral. This value is changed by eating Hero Fruit and Dark Fruit, using Hero and Dark characters to interact with the Chao, and the Chao being in the Hero Garden and Dark Garden. Hero Garden will cause an increase of +0.008333333768, or roughly 1/120, in alignment value about every 2 minutes, while Dark Garden will cause a decrease by -0.008333333768, or roughly 1/120, in alignment value about every 2 minutes. Through this method, a Chao should be ready to evolve into Hero or Dark alignment simply by being in the respective Hero or Dark Garden, with no player input, after 2 hours.

A value ≤ -0.5 will cause the Chao to evolve into a Dark Chao, and a value ≥ +0.5 will cause the Chao to evolve into a Hero Chao. The alignment value must be > -0.5 and < +0.5 to become a Neutral Chao.

Actions that affect alignment
Action Hero Characters Dark Characters
Petting with Heart appearing +0.05 -0.05
Picking up Chao with Heart appearing +0.033 -0.033
Give fruit with Heart appearing +0.01 -0.01
Give fruit with Heart appearing (Child) +0.025 -0.025
Give Animal or Chaos Drive +0.01 -0.01
Give Animal or Chaos Drive (Child) +0.025 -0.025
Chao eats the last bite of Hero Fruit +0.150 +0.150
Chao eats last bite of Dark Fruit -0.150 -0.150
Chao given a fruit they dislike -0.1 +0.1
Take fruit away from Chao -0.1 +0.1
Throw Chao -0.066 +0.066
Attack / Jump on Chao -0.1 +0.1

Evolution Strength

A Chao will evolve and enter its Cocoon when its Evolution Strength becomes full. The Evolution Strength is a value which runs from 0 to 1 for child Chao. A Chao is born with an Evolution Strength value of 0, and will evolve when it reaches 1. Evolution Strength can only increase in value, and does so as a Chao ages and eats fruit. Every bite of fruit, for unevolved child Chao, increases Evolution Strength by 0.005. The Evolution Strength value will increase about every 2 minutes by 0.01666667, or 1/60. This makes evolution timing mostly a function of age, with every bite of fruit getting the Chao about 1 minute closer to evolution. Eating a complete fruit (consisting of 4 bites) will allow your Chao to get 3.5 minutes closer to evolution. It should take about 3 hours for a child Chao to evolve, if it doesn't get fed at all.

Once a Chao evolves, it's Evolution Strength resets to 0 and gradually increases up to 1.2 (or 1.5 in Sonic Adventure 1.) At this stage the Evolution Strength will dictate Second Evolution or Gradual Evolution, the higher the Evolution Strength, the more developed the Chao's Second Evolution will appear. Adult Chao gain around 0.00125 (or 1/800) Evolution Strength for every bite of fruit. The growth rate of Evolution Strength while spending time in the Chao Garden is a quarter as fast as child Chao, therefore it increases about 0.00416667 (or roughly 1/240) every 2 minutes. It should take roughly 12 hours for an adult chao to get its Evolution Strength to 1.0, and 14.5 hours to 1.2, if it doesn't get fed at all. In Hero Garden the increase in Evolution Strength for Adult Chao over time is doubled to 0.008333334 (or 1/120) and in Dark Garden there is no increase in Evolution Strength over time.