Pak Protector
Pak Breeders and Pak Protectors are two developmental stages of fictional life in Larry Niven's Known Space universe. The Pak first appeared in "The Adults," which appeared in Galaxy in 1967; this story was expanded into the novel Protector by Larry Niven (1973). The Pak also appear in several of Niven's later novels, notably those set in the Ringworld.
Destroyer of Worlds depicts a confrontation between the Pak and the Puppeteers.
Narrative purpose
Niven has written that he invented the Protectors as a thought experiment to explain the common effects of aging on humans and to create a fictional evolutionary explanation for humans' long lives after females have passed reproductive age. Accordingly, most of the positive attributes of Protectors are based on negative human aging effects: swollen joints, decreased muscle-fat ratio, weakening heart, invariant diet, decreasing height, facial atrophy, leathery skin, hair loss, lack of sex drive, and tooth loss are all turned to advantage during the shift from Breeder to Protector.