From SC2Pod
The Spawning Pool gives Larvae the ability to morph into Zerglings and the Hatchery the ability to evolve into the Lair. The Spawning Pool is also responsible for evolving the Zergling with Metabolic Boost (faster movement) and Adrenal Glands (faster attack).
Lore
Contained within the primordial ooze of the Spawning Pool is the basic genetic makeup of the most prolific of the Zerg warrior breeds, the ravenous Zergling. Once grown, the Spawning Pool provides this genetic information to any Larvae produced by the same cluster, allowing them to metamorph into Zergling.
Research
StarCraft 2
The
Spawning Pool is still an important part of the Zerg base in StarCraft 2. It has seen little change. It still enables the production of
Zerglings and researches upgrades to enhance them.