The evolution chamber is the result of the Overmind's view that complacency is the road to defeat, causing it to spur zerg evolution constantly. The evolution chamber provides a testing ground for the genetic code of lesser breeds, helping to increase the offensive and defensive capabilities of the zerg ground-based breeds. It is also required in order for a creep colony to mutate into a spore colony.
The base of the evolution chamber forms from the genetic template of an unknown creature. During development, the "chamber" grows around a full skeleton with a skull, spinal column and ribs, that falls apart when the pit is destroyed. The biological roots of this creature is still unknown to terran scientists.
The evolution chamber contains a hardened skin that grants it near immunity to small arms fire, though can still be destroyed through mass C-14 rifle fire. In addition, it possesses genetic transmission appendages that allow it to transmit genetic information to other structures of the hive cluster.
Unlike its alpha appearance, the evolution chamber's form in the StarCraft beta was mostly identical to its end version, though had a distinctly more withered appearance. In some builds of he beta, the evolution chamber was named the "spore colony," a name which would later be given to a different structure