Pak Protector is not analogous to any human form. It is described as a 'fighting machine,' with armor-like skin, super-human strength and super-human intelligence. Niven's stories which focus on the Pak mostly concentrate on the unique Protector-stage.
Niven explained the evolution of the Pak as resulting from high radiation levels on their home world 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.
Read more about Pak Protector: Tree-of-Life, Protector Behavior, The Pak and Humanity
Famous quotes containing the word protector:
“My profession brought me in contact with various minds. Earnest, serious discussion on the condition of woman enlivened my business room; failures of banks, no dividends from railroads, defalcations of all kinds, public and private, widows and orphans and unmarried women beggared by the dishonesty, or the mismanagement of men, were fruitful sources of conversation; confidence in man as a protector was evidently losing ground, and women were beginning to see that they must protect themselves.”
—Harriot K. Hunt (1805–1875)