"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, like all children. But unlike other children, she didn't care about the damage she inflicted. A few miles away, Lenny Skutnik cared so much about others that he jumped into an ice-cold river to save a drowning woman. What is responsible for the extremes of generosity and cruelty humans are capable of? By putting psychopathic children and extreme altruists in an fMRI, acclaimed psychologist Abigail Marsh found that the answer lies in how our brain responds to others' fear. While the brain's amygdala makes most of us hardwired for good, its variations can explain heroic and psychopathic behavior. A path-breaking read, The Fear Factor is essential for anyone seeking to understand the heights and depths of human nature"--