toi don't change into a werewolf like humans do when they become vampires. There's supposed to be a certain gene in your family bloodline that decides if toi will be a werewolf ou not. If a person has this gene, he needs to reach a certain age before he can have his first change. And his first change can be provoked par strong emotions such as anger, rage, jealousy, hurt, etc. The werewolf-gene is passed down from father to son, father to daughter is also possible but the daughter can not pass down the gene like a son can (I know, UNFAIR!!!!)
Daughters can pass it on too. Otherwise, only the Black, Uley and Ateara families would have werewolf members. The other pack members must have inherited being a werewolf from a maternal line somewhere in their family.
The capability is hereditary. It then gets activated par the presence of a nearby vampire sometime in the werewolf's teens ou early twenties. They have a growth spurt, become feverish and their senses get enhanced. Finally, they phase into a loup for the first time triggered par anger.
