Homeworld of the Pak. The planet has high radiation levels and lies near the core of the Galaxy. The high radiation near the star-dense core caused severe mutations that can destabilize the evolutionary process. As a result, the Pak evolved a mechanism to eliminate dangerous mutations from the population. That mechanism is the protector stage.
Protectors are highly sensitive to the smell of their close relatives and 'weed out' those that smell wrong, which may indicate a potentially dangerous mutation. This weeding also suppressed positive mutations, essentially halting Pak evolution. Protectors are fully sentient, and are far more intelligent than ordinary humans. However, this superior intelligence only serves a Pak Protector's instincts to protect its bloodline at any costs.
The change from Breeder to Protector is the result of a peramorphic transformation brought about by the plant known as Tree-of-Life. As humans (and all primates) are descended from the Pak, Tree-of-Life can create a Protector-stage human.