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. 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. In Protector, the audience learns that humans are descended from the Pak. Pak Children and Breeders appear in Earth's fossil record as Homo habilis; the few Pak Protectors to make it to Earth apparently are not found in the fossil record. The Pak species goes through three stages of development: 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.