Evolution pit

The evolution chamber aboard Sarah Kerrigan's leviathan is controlled by Abathur, the evolution master.

Mutations
The player can select up to three mutations for each unit. The player can switch mutations between missions.

Zergling
 * Adrenal Overload: +50% attack speed.
 * Hardened Carapace: Gain an additional 10 hp.
 * Metabolic Boost: +60% movement speed.

Baneling
 * Corrosive Acid: Increase damage to primary target by 100%
 * Regenerative Acid: Heals nearby friendly units and structure
 * Rupture: Increase splash damage area by 50%.

Roach
 * Adaptive Plating: Gain +3 armor when life falls below 50%
 * Hydriodic Bile: Gain +8 damage vs. light units.
 * Tunneling Claws: Move at full speed when burrowed, and gain 100% life regen rate.

Hydralisk
 * Ancillary Carapace: Gain +20 HP.
 * Frenzy: Gain +50% attack speed for 15 seconds, with 30 second cooldown.
 * Grooved Spines: Gain +1 attack range.

Evolving Units
Each unit features a final, irreversible choice. For instance, the zergling can become a raptor (which gains combat bonuses) or a swarmling (which spawn in greater numbers).

Abathur inserts DNA sequences into the breed's genome for each mutation, but they fit into the same place.

Evolutions are acquired in one of 14 or so short skirmishes far from the standard missions. This allows the player to play two mini-missions where native critters are harvested, concluding with a unit demonstration where the newly-evolved units attack a small enemy force.

Examples
In one example, zerglings can be upgraded into raptors by absorbing the genetics of leaping creatures, while the alternative is to listen to a on a remote world who has developed swarmlings.

Another example of an evolution mission involved banelings. Abathur arranged for banelings to evolve into splitterlings on one planet by absorbing the genetic essence of its indigenous lifeforms. Alternatively, the banelings could be subjected to natural selection on a volcanic world, where lava flows kill many until they evolve jumping abilities to avoid that.

List of Evolutions
Zergling
 * Raptorling: Gains the ability to leap up and down cliffs and over other units.
 * Swarmling: Swarmlings spawn at 3 units per egg, and their spawn speed is drastically decreased (near instant).

Baneling
 * Splitter baneling: Banelings split into smaller banelings upon detonation, each smaller baneling does 5 damage.
 * Hunter baneling: Banelings gain the ability to jump up and down cliffs, as well as leap toward opponents.