Evolution pit/Development

The  underwent considerable change during the development of StarCraft II: Heart of the Swarm.

Formerly called the evolution pit, the structure enabled changes to units.

Each unit featured three upgrades and a final, irreversible choice. For instance, the zergling can get the Metabolic Boost, Posthumous Mitosis, and Rapid Genesis upgrades. Afterward it could become a raptor (which gains combat bonuses) or a swarmling (which spawn 3:1).

As zerg units were unlocked/developed, they would fill up the evolution pit&mdash;similar to the from Wings of Liberty. These mutations were made "on the fly" during gameplay.