ruthless and quite amoral. It is observed several times that this intelligence combined with instinct also compels action so completely that Protectors often have little "free will". Niven uses this trait as a plot device several times as characters set up circumstances where Protector characters will react in a specific manner. In Protector, Jack Brennan (a human turned into a Protector) commits genocide by exterminating the Martian race ("Aliens were dangerous, or might be, and Pak were not interested in anything but Pak") and also releases a genetically modified Tree-of-Life virus on the colony world Home, turning everyone middle aged into a Protector (and killing all other humans on the planet) in order to create an army of childless Protectors with which to fight the invading Pak fleet. It is indicated throughout Niven's works that humans (Homo sapiens) that have turned into protectors are far more intelligent than their Pak (Homo habilis) counterparts (in much the way that humans are more intelligent than the primates they evolved from). Niven explains much of Protector behavior in his Future History, by revealing in Ringworld's Children that the ARM may be run by at least one Protector and that Boosterspice (which dramatically prolongs human lifespan) is derived from Tree-of-Life. The Pak and humanity In Protector, Niven explains that humans (and all of Earth's primates) are descended from a colony of Pak breeders that were stranded on Earth 2.5 million years ago. The protectors that built the colony ship died when their Tree-of-Life crops failed. The original Pak Breeder population (known to us as Homo habilis) bred and mutated wildly, evolving into modern humans as well as all other Earth primates. All Terran primates would transform into the Protector stage if exposed to Tree-of-Life root (or, more accurately, the symbiotic virus it contains). In The Ringworld Engineers, the characters find evidence that the Ringworld was built by Pak Protectors (confirmed by the statements of a character in Ringworld's Children who claims to be one of the original builders) and populated by Pak breeders. The Pak Protectors dwindled in numbers until they were no longer able to maintain the genetic purity of the breeder forms and the breeders eventually evolved into all the other hominids of the Ringworld that one sees in Larry Niven's novels. In Destroyer of Worlds (co-written by Niven and Edward M. Lerner), a human world (and the Pierson's Puppeteers of the