Editing Pak Protector (section)

== Tree-of-Life ==

{{Redirect|Tree-of-Life|other uses|Tree of life (disambiguation)}}

[[Tree-of-Life]] is the mechanism by which a Breeder becomes a Protector. The term originally is used to refer to a specific plant which, when consumed, triggers the transformation. The term "Tree-of-Life virus" is used to describe the [[symbiosis|symbiotic]] virus which actually governs the transition.

Niven took the name Tree-of-Life from the [[Book of Genesis]]; specifically to the fruit of the "Tree of Life" that could make Adam and Eve immortal (Genesis 3:22–24), which is quoted as the foreword to the novel [[Protector (novel)|''Protector'']], and also mentioned by Brennan within the novel.

Tree-of-Life (the plant) is a bush native to the Pak homeworld. When a Breeder reaches the proper age (early 40s for humans), the smell of the root becomes irresistible; the Breeder gorges on the Tree-of-Life root, infecting itself with the Tree-of-Life virus and transforming into a Protector. The age window for the metamorphosis is relatively narrow (between 42 and 50 Earth years). Tree-of-Life is common on the Pak world, so there is almost no risk of a Breeder living past this window without being exposed to the roots.

The transition from Breeder to Protector involves reconfiguration of the anatomy. Skin thickens, becoming similar to leather armor, strong enough to turn a copper knife. Joints swell until the creature becomes "a parody of the human form done in [[cantaloupe]]s and [[coconut]]s". This increases leverage available to muscles by increasing the force of the [[moment (physics)|moment arm]], the result being that a protector can lift ten times its own weight. Genitalia and gonads vanish, and a second two-chambered heart forms in the groin at the fusion of the [[femoral vein]]s. The arms lengthen. Fingernails turn into retractable claws. Teeth fall out and the lips and gums fuse, the mouth forming a horny beak (flat in protectors transformed from humans, non-flat in protectors transformed from Pak). All the breeder's hair falls out and the head acquires a bony ridge to protect the newly expanded [[skull|cranium]]. The expanded skull allows the brain to grow to an enormous size; the resulting mind, even starting from something as "unintelligent" as a chimpanzee, becomes far more intelligent than a typical human. Pak Protectors also acquire an extended lifespan, and can live tens of thousands of Earth years (a common element in Niven's stories).

Once the transformation is complete, a Pak Protector must periodically consume more Tree-of-Life root to maintain the virus in its body. Without the virus, a Protector will weaken and die as its DNA is degraded; the virus supplies replacement DNA.

The Tree-of-Life crop on Earth failed due to there being insufficient [[thallium oxide]] (which particular oxide is never explained) in the Earth's [[Abundance of elements in Earth's crust|soil]]; the plants grew but did not support the virus. As a result, the Protectors that led the colony to Earth died of starvation when their store of roots ran out.