Why do some people enjoy taking risks while others avoid it at all costs?
Scientists have determined that a gene called neurod2 controls development of the part of the brain, called the amygdala, central to emotions and the ability to sense danger. "It's designed to keep us out of dangerous situations by helping us store in our long-term memory moments that are especially frightening or emotionally stressful."
Labratory mice modified to be deficient in the neurod2 gene became essentially fearless, relaxing in vulnerable, open, lit spaces and casually letting researchers pick them up.
They'd probably skydive, too, if we made them some little harnesses...