Not every member of the Quileute tribe has the potential to transform into a werewolf. Only those who can trace a direct bloodline back to the first shape-shifter, Taha Aki, are born with the potential to become shape-shifters themselves. The first transformations occurs between the onset age of puberty and approximately age twenty-five, and is based on two factors: heritage and the proximity of vampires.
The direct descendants of Taha Aki are born with twenty four chromosomal pairs rather than the twenty three pairs of a normal human. It was once believed that the extra chromosome could be passed down only to male descendants. but that was proven false; in eclipse, we saw the first female tribe member transformed.
This extra chromosome will not have any effect on the character if her or she is not in close proximity to vampires during all or part of the critical time between the onset of puberty and the age of twenty-five. If the potential werewolf is not exposed to vampires within the window of time, transformation will never occur. It is the scent of the vampire that triggers the reaction; a potential werewolf would not have to actually see or touch a vampire, only cross his scent.
signs of imminent transformation:
If a tribe member meets both conditions for transformation, he will go through a number of physical and psychological changes. First, a male will undergo a noticeable growth spurt, affecting both height and musculature. For a female, the physical changes are more subtle, mainly denoted by definition of muscle rather than bulk or height. Both males and females will then experience a drastic rise in body temperature, one that a typical human would be unable to survive. At the same time, he or she will begin to have dramatic mood swing and brief, sudden episodes of nearly uncontrollable rage. When the transformation is very close, he of she will begin to tremble and shake during these moments of rage.
After the shaking begins, the first transformation, or phase, can happen within seconds if the affected person does not calm himself. All the initial transformations are triggered by rage, until the werewolf can learn to control his reactions. The actual act of phasing last only an instant. There is no gradual shift, no in-between form where the werewolf appears to be a mix of human and animal. Because the wolf has more than four times the mass of the human, to an outsider the change looks explosive as the human expands to the size of the wolf. This impression can be intensified if the werewolf did not have time to remove his clothes before phasing; the clothes rip apart from the pressure of the expansion, adding a tearing sound to the otherwise soundless transformation.
Young werewolves are often unable to control their phasing, shifting forms whenever they feel anger. This unpredictability, combined with the massive size of the wolf form and the suddenness of the phasing process, makes werewolves dangerous to any humans in proximity to them during the change. Standing too close to a young werewolf during phasing can result in unintentional injury, or even death.
As young werewolves gain more control over their phasing, they have time to remove clothing, preventing it from being destroyed in a shape-shifting process. Most carry a leather strap with them so they can tie their clothes to their legs before phasing.