In “Origin,” Jessica Khoury’s debut young adult novel, the author explores a well known theme — the quest for immortality — and puts a new variation on it: What is the value of one’s life, and the lives of others, to someone who is already immortal? Pia is one of a kind — literally, in that she is the first and only immortal human being to ever exist. Her whole life, she has been sequestered away from civilization in a secret laboratory deep in the Amazon jungle.