At only 19-years-old, Abigail Marsh had a near-death experience. A dog ran in front of her car on the highway. When she served to avoid it, her car spun out, and she found herself facing an oncoming lane of traffic. Her engine was unresponsive. But another driver across the highway saw her emergency lights flashing, pulled over, and ran to her aid, writes National Geographic. He pushed her into the passenger seat, kicked her engine into gear, and drove her to safety. He then disappeared. Marsh never saw the man again. Since then, Marsh, now an associate professor of psychology and neuroscience at Georgetown University, as been looking to answer the questions: What makes someone put his life in danger to help a person he’s never met? Why do other people intentionally cause harm and feel no regret? Her new book, The Fear Factor, includes Marsh’s theory why one ancient part of the brain — the amygdala — controls how we identify and respond to fear. The amygdala recognizes people’s fear, and children who are psychopathic show a reduced amygdala response when they are shown pictures of fearful facial expressions. Their amygdala was also smaller. They have a “fearless personality,” Marsh told National Geographic. Altruistic kidney donors — people who donate their kidneys to complete strangers — had larger and more responsive amygdala. But surprisingly, Marsh said doing this type of work is uplifting. “Studying people who are psychopathic actually makes me optimistic about everyone else,” she said.
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