Book excerpt: In this "compelling scientific detective story," a leading neuroscientist looks for the nature of human kindness in the brains of heroes and psychopaths (Wall Street Journal). At fourteen, Amber could boast of killing her guinea pig, threatening to burn down her home, and seducing men in exchange for gifts. She used the tools she had available to get what she wanted, and, she didn't care about the damage she inflicted. A few miles away, Lenny Skutnik was so concerned about the life of a drowning woman that he jumped into the ice-cold river to save her. How could Amber care so little about others' lives, while Lenny cared so much? Abigail Marsh studied the brains of both psychopathic children and extreme altruists and found that the answer lies in our ability to recognize others' fear. And as The Fear Factor argues, by studying people who demonstrate heroic and evil behaviors, we can learn more about how human morality is coded in the brain. A path-breaking read, The Fear Factor is essential for anyone seeking to understand the heights and depths of human nature.